1 Evaluation of performance and carcass traits for a five-cohort All Heifer, No Cow beef production system demonstration herd Meredith A. Harrison,†,1 Jose A. Arce-Cordero,†,2 George E. Seidel Jr,‡ Shawn L. Archibeque,† Jack C. Whittier,†,3 Ryan D. Rhoades,† and Jason K. Ahola†,4 †Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523–1171; and ‡Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80523–1683 ABSTRACT: The All Heifer, No Cow (AHNC) beef production system is an alternative to con- ventional cow/calf production that involves in- semination of nulliparous heifers with sexed semen to produce female calves that are early weaned at 3 mo of age. Dams are finished on a high-concentrate diet and harvested before reach- ing 30 mo of age. Objectives of this research were to document reproductive, feedyard, calf, and carcass performance of an AHNC herd; evaluate effects of carcass maturity on carcass quality; and determine if performance of initial cohorts (i.e., cohorts 1 and 2) differed from sustaining cohorts (i.e., cohorts 3–5). A total of 272 heifers were en- rolled in the AHNC system via five annual co- horts. The system was initiated with 51 yearling, Angus-based heifers, and a replicate set (n = 56) was started 12 mo after. Heifers in cohorts 3 (n = 53), 4 (n = 56), and 5 (n = 56) were primarily offspring of prior cohorts (i.e., cohort 3 heifers born to cohort 1 females), but some were pur- chased to maintain inventory. Angus replacement heifers were purchased in cohorts 3 (n  =  26), 4 (n  =  26), and 5 (n  =  28). Mean (±standard de- viation) pregnancy rate at 30 d after fixed-time artificial insemination (AI) with sexed semen was 50.8% ± 9.4%, and 140-d pregnancy rate was 93.0% ± 1.5%. With AHNC, 61.0% ± 6.5% of fe- males replaced themselves with a heifer. During finishing, average daily gain (ADG) was 1.9  ± 0.4  kg • d−1 and dry matter intake (DMI) was 14.9  ± 1.9  kg • d−1. Hot carcass weight (HCW) was 367 ± 35 kg. The USDA grading system clas- sified 20.5% of all carcasses (n = 220) as C ma- turity (A00 = 100, B00 = 200, etc.), 62.4% ± 29.1% of carcasses as USDA Choice. USDA yield grade (YG) was 2.6  ± 0.7. Based on cohorts 1 and 2, there were no differences (P = 0.96) in Warner– Bratzler shear force values between A and B ma- turity vs. C maturity carcasses. Across all cohorts, there were no differences in USDA YG, marbling score (MA), and lean maturity between A  and B maturity vs. C maturity carcasses; there were differences in age (P  <  0.001), bone maturity (P  <  0.001), and overall maturity (P <0.001). A  comparison of initial vs. sustaining cohorts showed that initial cohorts had lower (P < 0.001) DMI, heavier (P  <  0.001) HCW, and more ad- vanced (P < 0.05) bone maturity. However, there were no differences for 30- and 140-d pregnancy rates, ADG, USDA YG, and MA between initial and sustaining cohorts. The AHNC beef produc- tion system can effectively produce female calves and quality carcasses for harvest. Key words: beef production system, biological efficiency, cattle, sex-selected semen, single-calf heifer 1Present address: Department of Animal Science, Univer- sity of California, Davis, CA 95616 2Present address: Department of Animal Sciences, University of Florida, Gainesville, FL 32611 3Present address: Panhandle Research and Extension Center, University of Nebraska, Scottsbluff 69361 4Corresponding author: jason.ahola@colostate.edu Received June 11, 2020. Accepted October 23, 2020. D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 mailto:jason.ahola@colostate.edu?subject= 2 Harrison et al. Translate basic science to industry innovation © The Author(s) 2020. Published by Oxford University Press on behalf of the American Society of Animal Science. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non- Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commer- cial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com Transl. Anim. Sci. 2020.XX:0-0 doi: 10.1093/tas/txaa191 INTRODUCTION Conventional beef production in the United States is typically specialized, encompassing for- age-based cow/calf production through inten- sively managed feedyards that finish cattle on grain and other concentrates. Often there is an intermediary, grass-based stocker segment be- tween cow/calf and feedyard segments. In beef production, feed nutrients are partitioned to growth/development, lactation, reproduction, fat accretion, and maintenance (Ferrell and Jenkins, 1985). Collectively, considering cows’ require- ments combined with energy requirements of replacement heifers and bulls, about 70% of all nutrients consumed for beef production are ex- pended by the cow/calf segment (Ferrell and Jenkins, 1985). The remaining 30% account for postweaning growth of calves during both stocker and feedyard segments. About 75% of all nutri- ents consumed by the cow/calf segment are for maintenance energy. Thus, integrated over the en- tire U.S. beef production system, nearly one-half of all nutrients consumed are utilized for cowherd maintenance energy (Ferrell and Jenkins, 1985). Researchers analyzing beef production feed efficiency have reported that the greatest effi- ciency can be achieved by harvesting females shortly after the birth of their first calves (Taylor et al., 1985; Bourdon and Brinks, 1987). The All Heifer, No Cow (AHNC) beef production system produces beef without mature cows, inseminat- ing nulliparous heifers with female sex-selected semen to produce primarily female calves that are early weaned 3 mo after parturition. After weaning, dams are finished on a high-concen- trate ration and harvested before reaching 30 mo of age (Seidel and Whittier, 2015). Minimal per- formance data exist in the scientific literature that characterize this production system, thus limiting the ability of researchers to evaluate potential im- proved efficiencies that may result from this alter- native beef production system. Objectives of this study were to: 1) document re- productive, feedyard, calf, and carcass performance of a five-cohort AHNC demonstration herd; 2)  evaluate effects of carcass maturity on carcass quality variables; and 3) determine if performance of initial cohorts (i.e., cohorts 1 and 2)  differed from sustaining cohorts (i.e., cohorts 3 through 5). MATERIALS AND METHODS Animals All animals in this study were managed under the approval of the Colorado State University Institutional Animal Care and Use Committee guidelines. A total of 272 heifers were enrolled in the AHNC beef production system via five annual cohorts over a 6-yr period. The system was initi- ated in March 2013 (i.e., cohort 1)  with the pur- chase of 51  yearling, Angus-based commercial heifers with an initial body weight (BW) = 354 ± 39 kg. A replicate set of similar heifers (n = 56; ini- tial BW = 307 ± 30 kg) was purchased and enrolled the following year. With this system, annual income requires two herds, 12 mo apart in age from each other. One herd is being bred approximately the same time dams and calves from the other set enter the feedyard (Seidel and Whittier, 2015). Exact ages of heifers in cohorts 1 and 2 were not known, but heifers were estimated to be 1 yr of age at purchase. Upon arrival, heifers were weighed, body condition scored, ear tagged, and rectally pal- pated to eliminate freemartins and reproductive tract abnormalities. Heifers enrolled in cohorts 3 (n = 53), 4 (n = 56), and 5 (n = 56) were primarily the offspring of prior cohorts (i.e., cohort 3 heifers were born to cohort 1 females). The numbers of re- placements raised within the AHNC beef produc- tion system were 28, 32, and 28 for cohorts 3, 4, and 5, respectively. The remaining heifers were acquired in a similar manner as cohorts 1 and 2 to ensure the maintenance of annual herd inventory. Purchased replacement heifers for cohorts 3 through 5 were Angus heifers. Birthdates were known on all heif- ers for cohorts 3 through 5. Animals were main- tained at East Rabbit Creek Ranch in Livermore, CO, and the feedyard at the Colorado State D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 http://creativecommons.org/licenses/by-nc/4.0/ mailto:journals.permissions@oup.com?subject= 3Evaluation of an All Heifer, No Cow beef herd Translate basic science to industry innovation University Agricultural Research, Development, and Education Center in Fort Collins, CO. Ovulation Synchronization to Weaning Ovulation was synchronized with a 14-d con- trolled internal drug releasing (CIDR) insert (Eazi- Breed; Zoetis, Parsippany, NJ). On day 17 after CIDR removal, estrus detection patches (Estrotect; Rockway Inc., Spring Valley, WI) were placed in front of tail heads, and heifers received an intra- muscular (i.m.)  injection containing 25  mg of prostaglandin F2 alpha (PGF2α) (Lutalyse; Zoetis, Parsippany, NJ). Approximately 66  h after PGF2α injection, patch status was assessed, and heifers with activated patches were inseminated with 0.25 cc of female sex-selected semen. Heifers with inactivated patches at 66  h after PGF2α injection received an i.m. injection of 100 μg of gonadotropin releasing hormone (GnRH) (Factrel; Zoetis, Parsippany, NJ) and were inseminated 18 h later with 0.25 cc of fe- male sex-selected semen. Cohorts 1 and 2 were in- seminated with semen from polled Hereford bulls, so cohorts 3 and 4 were predominantly Angus × Hereford. Heifers in cohorts 3 and 4 were insem- inated with semen from a polled, black Simmental bull with high breeding values for calving ease and carcass characteristics. Cohort 5 was inseminated with semen from a Hereford or Simmental sire that was used in a previous cohort or an Angus sire that was not previously used. Cohorts 2 through 5 had ovulation resynchro- nized. Resynchronization of ovulation was initiated 12 d after timed AI with the insertion of an intra- uterine CIDR. After 7.5 d, CIDR were removed, and estrus detection patches were applied. Heifers were observed for behavioral signs of estrus at least twice daily (i.e., am and pm). Heifers displaying standing estrus in the pm were inseminated the following am. On average, heifers were inseminated approxi- mately 3.5 d after CIDR removal. Generally, heifers that were inseminated a second time were bred to the same sire as their first insemination. Heifers that did not exhibit estrus were assumed to be pregnant to the first AI and were not inseminated a second time. Immediately following the second AI, heifers were placed with a natural service sire. For cohorts 1 and 2, a polled Hereford bull was used. In cohorts 3 and 4, a Gelbvieh × Angus bull was used. In cohort 5, a black Angus bull was used. Heifers remained with the bull uninterrupted for approximately 100 d. Since cohort 1 did not receive a second AI, the natural service sire was immediately placed with the heifers after the first AI. Pregnancy rate to the first AI was diagnosed 33 to 36 d after the first AI via ultrasound (Aloka 500; Corometrics Medical Systems, Wellington, CT) fitted with a 5-MHz rectal probe. A  second pregnancy diagnosis was performed by rectal pal- pation 140 d after the first-timed AI to determine season-long pregnancy rate. Following the second pregnancy diagnosis, nonpregnant heifers and heif- ers that conceived late in the breeding season (i.e., pregnancy determined to be less than 90 d) were sold. Heifers were maintained on native range May through November and were fed hay December through April. At parturition, date of birth, calving ease score, calf birth weight (BWT), and calf sex were recorded. After calving, dams were supple- mented with 15% crude protein (CP) range cubes at an average level of 1.4 kg • dam−1 • d−1. Management From Weaning to Harvest Two weeks prior to early weaning, dams and calves were jointly shipped 45 km to the feedyard Table 1. Description of variation in management across the five-cohort AHNC demonstration herd during feedyard phases Management factor Cohort 1 Cohort 2 Cohort 3 Cohort 4 Cohort 5 Time on grass hay, d 1 8 3 2 2 Time on receiving ration, d 6 – 22 12 9 Time on transitioning ration, d 11 21 16 21 15 Time on finishing ration, d 72 80 61 79 70 Total time in the feedyard, d 90 109 102 115 96 Time in the feed intake unit, d 42 48 – – – Steam-flaked corn used in mixed ration in place of cracked corn – – – YES – Implanteda YES YES – YES YES Melengestrol acetate in finishing mixed ration – YES YES YES YES Calves fence-line weaned – YES YES YES – Lactation continued in some females prior to harvest – – – YES – aRevalor-H (Intervet, Madison, NJ). D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 4 Harrison et al. Translate basic science to industry innovation and placed into a single pen with a concrete bunk and ad libitum access to water. Dams and calves re- ceived ad libitum grass hay for at least 3 d (Table 1). For the next 2 to 3 weeks, dams and calves in co- horts 1 and 3 through 5 were fed a receiving ra- tion. Cohort 2 was not fed the receiving ration but was transitioned directly from grass hay to a transitioning ration (Tables  1 and 2). Cohorts 1 and 3 through 5 were fed a moderate-energy, tran- sitioning ration for approximately 3 wk (Tables  1 and 2). While the transitioning ration was fed, calves were early weaned at 105  ± 21 d.  Cohorts 2 through 4 were weaned using fence-line weaning (Price et  al., 2003). In cohorts 1 and 5, calves were weaned by placing them in a pen at the op- posite end of the feedyard. Dams were implanted in the right ear with 200 mg of trenbolone acetate and 20  mg of ß-estradiol (Revalor-H; Intervet, Madison, NJ). Cohorts 4 and 5 were implanted at weaning, cohorts 1 and 2 were implanted 6 wk after weaning, and cohort 3 was not implanted (Table 1). At-weaning calves were retagged and weighed. After weaning, calves remained in the feedyard 50  ± 10 d on a moderate energy ration until re- turning to Rabbit Creek Ranch (Table 2). For the remaining time in the feedyard, dams were fed a high-energy, finishing ration (Tables 1–3). Finishing rations for dams in cohorts 2 through 5 were formu- lated to provide 0.5 mg of melengestrol acetate per dam per day until harvest. Dams received the fin- ishing ration for 72 ± 8 d until they reached a target harvest BW of 636 kg (Table 1). While calves and dams were in the feedyard, individual animal BW were collected at least every 3 wk in the morning prior to feeding. In cohorts 1 and 2, individual daily feed intake data were collected by an automated feed intake monitoring system (GrowSafe, Calgary, Alberta, Canada) in the specialized feed intake unit (FIU). Dams were individually tagged with radio fre- quency identification tags (TFIW/GESMW, Allflex, Airport, TX) that were placed on the left ear and were sorted and placed in two 25-animal pens with free access to water and concrete bunks (Arce-Cordero, 2016). Dams remained in the FIU for 42 and 48 d in cohorts 1 and 2, respectively (Table 1). Dams in cohorts 1 and 2 were weighed upon entry to the FIU and again on days 14, 28, and 42. Cohort 2 remained in the FIU for an add- itional week and was weighed on day 48 when exiting the FIU. Individual simple linear regres- sions were performed using animal BW data, ADG was predicted, and individual dry matter intake (DMI) and gain:feed (G:F) values were Table 2. Protein and energy content of rations fed to AHNC animals while in the feedyard by cohorta Nutrient composition (DM basis) Receiving ration (low energy) Transition ration (moderate energy) Finishing ration (high energy) Cohort 1b DM, % – 63.91 67.48 Net energy for gain, MCal • kg−1 – 0.48 0.64 CP, % – 16.48 12.58 Acid detergent fiber, % – 25.16 8.48 Cohort 2c DM, % – 63.91 67.48 Net energy for gain, MCal • kg−1 – 0.48 0.64 CP, % – 16.48 12.58 Acid detergent fiber, % – 25.16 8.48 Cohort 3d DM, % 70.20 71.24 – Net energy for gain, MCal • kg−1 0.36 0.58 – CP, % 14.74 14.43 – Acid detergent fiber, % 32.73 15.06 – Cohort 4 DM, % 71.24 67.09 73.37 Net energy for gain, MCal • kg−1 0.48 0.52 0.56 CP, % 15.61 17.81 14.45 Acid detergent fiber, % 18.31 14.09 8.90 Cohort 5 DM, % 80.00 69.46 77.52 Net energy for gain, MCal • kg−1 0.53 0.46 0.57 CP, % 16.52 15.50 12.15 Acid detergent fiber, % 20.01 20.77 7.17 aNutrient percentages were reported on a DM basis. bProximate analysis for the receiving ration from cohort 1 was unavailable. cCohort 2 was not fed the receiving ration. dProximate analysis for the finishing ration from cohort 3 was unavailable. D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 5Evaluation of an All Heifer, No Cow beef herd Translate basic science to industry innovation calculated. On days cattle were weighed, feed in- take data were omitted from analyses to ensure that external factors did not influence feed intake. After the conclusion of feed intake measurements, dams remained in the feedyard on the finishing ra- tion until harvest. For cohorts 3 through 5, total BW of the pen was calculated using individual animal BW meas- urements. The proportion of each animal’s indi- vidual BW to pen BW was calculated. Individual animal DMI was calculated by multiplying the pro- portion of individual animal BW to pen BW by the total amount of feed delivered to the pen daily. The proportion of individual animal BW to pen BW was recalculated when animal BW were updated every 3 wk. Gain:feed ratios were individually cal- culated using estimated DMI. Cohorts 2 through 5, dams were individually mouth scored to quantify the number of permanent incisors 3 wk prior to harvest. A  second mouth score was taken the day prior to harvest. In cohort 1, only a single mouth score was taken the day prior to harvest. Exit BW was individually calculated by averaging BW measured the final 2 d at the feed- yard. Shrunk BW was calculated using 4% pencil shrink between the feedyard and packing plant. Harvest Across all five cohorts, a total of 222 AHNC females were harvested at a commercial packing plant located 48 km from the feedyard. In cohorts 1 and 5, one carcass was unavailable for measure- ments. Researchers from Colorado State University recorded the following carcass measurements: pre- liminary yield grade (YG); adjusted preliminary YG; HCW; ribeye area (REA); percentage of kidney, pelvic, and heart fat; marbling score (MA); lean maturity score (LM); and bone maturity score (BM). Yield grade and quality grade (QG) were calculated and USDA YG and QG assigned by USDA grading personnel were recorded. Yield and quality grades and overall maturity score (OM) were calculated using standards outlined in USDA Beef Quality and Yield Grades (Hale et al., 2013). Maturity scores of 100, 200, and 300 coincided with maturities of A00, B00, and C00, respectively. Marbling score was assessed at the interface of the 12th and 13th rib and corresponded with the fol- lowing marbling levels: practically devoid00 = 100, traces00  =  200, slight00  =  300, small00  =  400, modest00  =  500, and moderate00  =  600. Dressing percentage was calculated using shrunk BW and HCW. For cohorts 3–5, age at harvest was calcu- lated using available birthdates. Since no birthdates were available for cohorts 1 and 2, age at harvest was not known. In cohorts 1 (n = 42) and 2 (n = 43) carcass meat tenderness was also evaluated. One 5-cm-thick lon- gissimus muscle sample was removed from the loin portion of each carcass’s left side at the interface of the 12th and 13th ribs. Longissimus muscle samples were used to evaluate slice shear force (SSF), Warner– Bratzler shear force (WBSF), and percentage of cooking loss. Longissimus muscle samples were packaged in vacuum-sealed bags and placed on ice for transport to the Colorado State University meat laboratory. Meat samples were repackaged in vac- uum-sealed bags and wet aged at 2 °С until day 14 postmortem. After aging, samples were sliced into 2.54-cm-thick steaks and oven cooked to a peak temperature of 71 °С (Rational D88899, Landsberg am Lech, Germany). Precooking and postcooking weights were recorded, and cooking loss was calcu- lated. After cooking, a 1-cm-thick, 5-cm-long slice was removed from each steak parallel to the muscle fibers. Samples were sheared perpendicular to the muscle fibers using a universal testing machine, (Instron Corp., Canton, MA) equipped with a flat, blunt-end blade to evaluate SSF. The same machine was fitted with a WBSF head, and two individual core samples were tested. The two peak force meas- urements from the core samples were averaged to calculate WBSF. Weaning to Ovulation Synchronization Recently weaned calves were transported from the feedyard to Rabbit Creek Ranch to graze fall pasture. Calves were supplemented daily with 15% CP range cubes at a level of 1.3 kg per animal. In all cohorts, steer calves were removed from the study and sold at a local auction market. Due to im- perfections in the accuracy of sex-selected semen, reduced fertility of sex-selected semen, use of a natural service sire, and calf and dam death loss, the AHNC beef production system was unable to derive 100% of its replacements from within the system. Thus, replacement heifers were purchased annually for cohorts 3 through 5. A  total of 80 Angus, replacement-quality heifers were purchased in cohorts 3 (n = 26; initial BW = 180 ± 6 kg), 4 (n = 26; initial BW = 222 ± 21 kg), and 5 (n = 28; initial BW = 228 ± 22 kg). In each cohort, the new set of heifers, including replacements, were trans- ported to the feedyard in early winter. Heifers were D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 6 Harrison et al. Translate basic science to industry innovation fed a moderate energy ration overwinter (99  ± 5 d; Table  2). Subsequently, heifers returned to the Rabbit Creek Ranch and were fed hay until May when the native range was available. Ovulation was synchronized as previously described. Data Analyses Data analyses were done using R (version 3.5.1). Descriptive statistics were used to calcu- late means (±SD) of key production parameters for reproducing females, calves, dams in the feed- yard, and carcasses. Pregnancy diagnoses, calving records, and production records from first and second inseminations were used to calculate per- centages of heifers that conceived to first fixed- time AI and remained pregnant and percentages of heifers that conceived to the second fixed-time AI or natural service sires. To evaluate differences in meat quality be- tween youthful (i.e., A  and B maturity) and mature (i.e., C maturity and greater) as classi- fied by USDA grading personnel based on car- cass maturity, a t-test was conducted. Carcasses were pooled across cohorts and sorted into two groups—youthful (i.e., OM <300) and mature (i.e., OM ≥300) carcasses based on assigned USDA grades. The resultant means for HCW, REA, YG, MA, LM, BM, OM, and dressing per- centage were compared. Slice shear force, WBSF, and cooking loss were compared on carcasses from cohorts 1 and 2. Individual cohorts were not statistically com- pared to other cohorts since that was not an ob- jective of this study. However comparisons were made between initial (i.e., cohorts 1 and 2)  and sustaining (i.e., cohorts 3 through 5) cohorts since the background, genetics, and lifetime manage- ment differed. To test for performance differences between initial and sustaining cohorts, regression analyses were used. Group referred to whether an animal was from initial or sustaining cohorts. Logistic regression and contrasts were used for 30- and 140-d conception rates, and pregnancy was treated as the response variable. Prebreeding BW, body condition score (BCS), and group were con- sidered as dependent variables. In the case of the 140-d regression, the categorical predictor repeat AI was also used (i.e., whether or not a heifer re- ceived a second AI). Age was not used as a pre- dictor variable because ages were unknown for the initial cohorts. Multiple linear regression models were fit to data to evaluate growth and carcass performance between initial and sustaining cohorts. Response variables considered were ADG, DMI, HCW, dressing percentage, USDA YG, MA, LM, BM, and OM. Predictor variables included for consid- eration were BCS and BW at prebreeding, con- ception to first AI, second AI exposure, presence of a live calf at weaning, days on feed, ADG, G:F, HCW, MA, LM, BM, OM, USDA YG, and group. Measurements for SSF, WBSF, and cooking loss were not included because they were only performed on cohorts 1 and 2. Model selection was performed using backward selection. Data collected on ani- mals that died were not used in analyses. Means were calculated using the emmeans package and reported as least squares means. Significance was declared at P ≤ 0.05 RESULTS AND DISCUSSION Reproductive Performance At prebreeding, BW for the five cohorts was 346  ± 45  kg, and body condition score was 5.5  ± 0.6 (Table  4). Overall pregnancy rate at 30 d after fixed-time AI with sex-selected semen was 50.8% ± 9.4%; however, the final two cohorts had an average 30-d post-fixed-time AI pregnancy rate of 56.3%. Considering the reduced fertility of sex-selected semen due to decreased sperm numbers, these re- sults were expected (Garner and Seidel, 2008). Seidel et  al. (1999) evaluated the effects of breed, sperm concentration, and semen deposition site on concep- tion rates for beef heifers inseminated with sex-se- lected semen and reported that pregnancy rates ranged from 26% to 86%. In a follow-up study, the average pregnancy rate for beef heifers inseminated with sex-selected semen 12–24 h after standing estrus was 55.9% (range: 47–80%), and sex-selected semen conception rates were typically 80% of conventional semen, but management played a key role in the suc- cess of breeding (Seidel and Schenk, 2008). In the current study, conception rates were within the re- ported range. However, conception rates improved in later cohorts; the unknown history of cohorts 1 and 2 may have negatively impacted breeding suc- cess, but improved conception rates were likely due to an improvement in semen sexing technology (Seidel, 2014; Vishwanath and Moreno, 2018). Riggs (2001) evaluated an integrated produc- tion system that included the use of early weaning, early breeding (i.e., 10 mo of age), and insemination with sex-selected semen. Conception rates to fixed- time AI with sex-selected semen were 19% and 8% in cohorts 1 and 2, respectively. However, at the D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 7Evaluation of an All Heifer, No Cow beef herd Translate basic science to industry innovation conclusion of the breeding season which included exposure to a natural service sire, conception rates were 58% and 16% for cohorts 1 and 2, respectively (Riggs, 2001). Riggs attributed low conception rates to only a small percentage of heifers cycling before the first AI. Results from the current study suggest that there are external management factors that also impact the success of insemination with sex-selected semen. In cohort 1, there was a numer- ical reduction in 30-d post-fixed-time AI pregnancy rate (41.2%) compared to other cohorts (Table 4). The reduced conception rate for cohort 1 was at- tributed to the lack of fertility information on bulls used, incomplete history on purchased heifers (e.g., age or previous implant status), and other manage- ment factors. Table 4. Summary statistics (mean ± SD) for reproductive performance of AHNC females by cohort and overall Parameter Cohort 1 Cohort 2 Cohort 3 Cohort 4 Cohort 5 Overall Females exposed, n 51 56 54 56 56 273 BW at estrus synchronization, kg 354 ± 39 307 ± 30 390 ± 44 336 ± 32 348 ± 38 346 ± 45 Body condition score at estrus synchronizationa 5.1 ± 0.8 5.1 ± 0.5 6.0 ± 0.3 5.7 ± 0.5 5.5 ± 0.5 5.5 ± 0.6 Pregnancy rate 30 d after fixed-time artificial insemination, % 41.2 48.2 51.9 46.4 66.1 50.8 ± 9.4 Pregnancy rate 140 d after fixed-time artificial insemination, % 94.1 92.9 90.7 92.9 94.6 93.0 ± 1.5 Heifers—failed to conceiveb, % 5.9 3.5 7.4 7.1 3.6 5.5 ± 1.9 Heifers— artificial insemination and remainedc, % 39.2 44.6 48.1 46.4 57.1 47.1 ± 6.5 Heifers—repeatsd, % – 35.7 33.3 35.7 19.6 31.1 ± 6.7 Heifers—bulle, % 54.9 32.1 33.3 32.1 30.4 36.6 ± 10.3 Heifers—late and soldf, % 7.8 10.7 0.0 7.1 8.9 6.9 ± 4.1 Calf cropg, % 94.1 85.7 74.1 81.8 92.9 85.7 ± 8.3 Calves born aliveh, % 100.0 88.9 81.6 88.2 98.1 91.4 ± 7.6 aBody condition scores were on a nine-point scale and included half scores (Herd and Sprott, 1996). bPercentage of heifers that were open at the 140-d pregnancy diagnosis. cPercentage of heifers that conceived to the first artificial insemination and remained pregnant. dPercentage of heifers that received a repeat artificial insemination; only a single artificial insemination was performed on cohort 1. ePercentage of heifers that conceived via natural service. fPercentage of heifers that conceived late (i.e., pregnancy less than 90 d at the 140-d pregnancy diagnosis) and were sold. g(N◦ weaned calves/ N◦ exposed females) × 100; heifers sold pregnant were assumed to wean a live calf. h(N◦ weaned calves/N◦ pregnant females) × 100; heifers sold pregnant were assumed to wean a live calf. Table 3. Ingredient composition of finishing rations fed to AHNC females by cohorta Itema Cohort 1 Cohort 2 Cohort 3 Cohort 4 Cohort 5 Alfalfa hay, % 8.1 8.1 – – – Wheat straw, % – – – – 4.6 Hay treatb, % 3.3 3.3 – – 5.9 Corn silage, % 30.0 30.0 28.6 24.7 24.0 Cracked corn, % 35.0 35.0 – 56.2 58.0 Steam flaked corn, % – – 63.3 – – Dried distillers grains, % 7.8 7.8 – 11.3 6.5 Limestone, % 0.3 0.3 – – 1.0 Salt, % 0.1 0.1 – – 0.1 Ionophorec, g • ton−1 149 149 – – – Melengestrol acetate, g • ton−1 1.0 1.0 1.0 1.0 1.0 Liquid supplementd, % – – 4.3 3.6 – Mineral supplemente, % – – 3.8 4.2 – aAll ingredients reported on a DM basis. bHay treat was a molasses-based supplement that included glycerin, urea, condensed fermented corn extractives, ammonium polyphosphate, zinc sulfate, manganese sulfate, copper sulfate, xanthan gum, sodium selenite, vitamin E, vitamin A, vitamin D, cobalt sulfate, and ethylenediamine dihydroiodide. cRumensin (Elanco Animal Health, Indianapolis, IN). dLiquid supplement consisted of calcium carbonate, urea, condensed corn distillers solubles, molasses products, attapulgite clays, water, salt, vitamin E, and vitamin A. eMineral supplement consisted of salt, zinc sulfate, iron carbonate, manganese sulfate, copper sulfate, and sodium selenite. D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 8 Harrison et al. Translate basic science to industry innovation At the conclusion of breeding seasons, 93.0% ± 1.5% of heifers were pregnant. A small number of heifers failed to conceive (19/272 = 7.0%) and were sold from the system (Table 4). The percentage of heifers that conceived to first AI and remained preg- nant (47.1% ± 6.5%), the percentage of heifers that received a repeat AI (31.1% ± 6.7%), and the per- centage of heifers that likely conceived to natural service (36.6% ± 10.3%) were calculated (Table 4). The numerical reduction between pregnancy rate at 30 d after AI (50.8%) and heifers pregnant to first AI and remained pregnant (47.1%; Table  4) was due to early embryonic death. The hastened system timeline (Fig.  1) in the current study required a timely conception. Overall, 6.9% ± 4.1% of exposed heifers achieved pregnancy but were sold because the projected calving date was outside the desired calving season (i.e., 50-d breeding season; Table  4). Heifers that calve late in the calving season will have difficulty achieving target harvest weight prior to reaching 30 mo of age. Furthermore, calves born later in the calving season would be younger and lighter at weaning and, thus, may struggle to achieve puberty in sufficient time for conception to the first AI. Although these preg- nant heifers are not suitable for this system, selling them as pregnant females is a viable strategy for off- setting the lengthy time to income associated with the AHNC beef production system. As shown in Table  4, the percentage of calf crop was 85.7% ± 8.3%. The 2007–2008 National Animal Health Survey for the cow/calf segment conducted by the USDA (2010) reported an average percentage of calf crop of 83.2% for primiparous females and 91.5% for all females. An evaluation conducted by Laster and Gregory (1973) evaluated parturition and calf death loss in a variety of cattle breeds and concluded that calf losses were greater in primiparous females than cows due to a greater number of assisted births with primiparous females. Similar results were reported by Patterson et  al. (1987) who documented the greatest calf mortality rates in primiparous females. Results showed that AHNC heifers were able to perform reproductively and achieved reproductive rates similar to those of conventional cow/calf production. Calf Performance Over the five-cohort study, a total of 213 calves were weaned. Combined across sexes and cohorts, calf BWT was 33 ± 5 kg (Table 5). There was a dif- ference (P < 0.001) in BWT between male (n = 51; 35 ± 10 kg) and female (n = 173; 32 ± 9 kg) calves. These results were consistent with Tubman et al. (2004) who concluded that heifer calves weighed an average of 1.9 kg less than their male contem- poraries. The difference between male and female BWT was also partly due to sire differences. Most female calves were conceived via AI sires with accurate expected progeny difference (EPD)  for calving ease, and most male calves were sired by natural service sires with less accurate EPD for calving ease. The reduction in the number of calves born (n = 224) and calves weaned (n = 213) was due to calf death loss prior to weaning. Calves were early weaned at 105  ± 21 d with an average weaning weight (WWT) of 125 ± 28 kg (Table 5). Calves from cohorts 1 and 2 were heavier (P  <  0.001) at weaning than calves in cohorts 3 Figure 1. General timeline for five cohorts of the AHNC beef production system. Annual income requires a second set of heifers (i.e., cohort 2) started 12 mo after the first. During subsequent years, a few additional commercial heifers enter the system prior to breeding to maintain system inventory. D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 9Evaluation of an All Heifer, No Cow beef herd Translate basic science to industry innovation through 5. The increased WWT for cohorts 1 and 2 was attributed to the increased (P < 0.001) age of cohort 1 and 2 calves at weaning but also to the un- known genetic history and age of dams in the initial cohorts. Calves gained 0.40 ± 0.08 kg • d−1 prewean- ing and 0.9 ± 0.3 kg • d−1 during the postweaning dry lot phase (Table 5). Reiling et al. (1995) reported an average WWT of 159 kg and preweaning ADG of 1.1  kg • d−1 for calves produced by once-calved fe- males (OCF) that were early weaned at 117 d of age. Similarly, Peterson et al. (1987) reported an average WWT and preweaning ADG for early weaned, cross- bred calves of 109 and 0.76 kg • d−1, respectively. An important measure for the AHNC beef production system is the percentage of females weaned. This will influence the number of replace- ments that must be purchased annually to maintain consistent herd inventory. Overall, 61.1% ± 6.5% of females replaced themselves with a heifer, although the final two cohorts averaged a replacement rate of 67.9% (Table 5). This number was slightly below initial expectations; the goal was to achieve a re- placement rate of 75%. Reduced accuracy and re- duced fertility of sex-selected semen, calf and dam death loss, and the use of natural service sires re- duced the percentage of female calves weaned. The AHNC beef production system would function with conventional semen, in which about 40% of females would replace themselves with a heifer but require purchasing more replacement heifers; how- ever, management burdens and insemination costs would be reduced. Feedyard performance Upon entering the feedyard, initial BW was 464 ± 54 kg (Table 6). Dams in cohort 1 were heavier upon entry to the feedyard (518 ± 49 kg), but dams in this cohort were assumed to have been slightly older than those in other cohorts since birthdates were unknown. This theory was supported by the greater percentage of C maturity carcasses based on carcass maturity in cohort 1. Overall, dams re- mained in the feedyard 102 ± 10 d prior to harvest and, majority of the time (72 ± 8 d), dams were fed a high-energy finishing ration (Tables 1 and 3). The length of the feeding period in the current study was consistent with previously reported feeding periods for primiparous and multiparous females. Schnell et al. (1997) concluded that feeding a grain- based diet for 56 d was a sufficient amount of time to convert yellow fat to white fat. A longer feeding period of 105 d was reported by Pritchard and Berg (1993) for cull cows ranging 4 to 10 yr of age. While on the finishing ration, overall ADG for dams was 1.9 ± 0.4 kg • d−1 (Table 6). The ADG ob- served in the current study was greater than ADG previously reported for OCF. Field et  al. (1996) fed a grain-based diet to crossbred OCF (entry BW  =  525  kg) for 100 d after early weaning of calves. Dams gained 1.3 kg • d−1 (Field et al., 1996). A similar study by Waggoner et al. (1990) evaluated Simmental × Hereford OCF that calved at 24 mo of age, were implanted, and fed a grain-based diet for 137 d prior to harvest, and ADG was 1.0 kg • d−1 (Waggoner et al., 1990). The ADG achieved by dams in the current study exceeded ADG values re- ported for conventionally raised and finished heif- ers (1.5  kg • d−1) and steers (1.7  kg • d−1; Kansas State Research and Extension, 2017). The increased rate of gain for dams in the current study com- pared to previously reported ADG was likely due to dams being lighter at the start of the finishing period. Furthermore, dams experienced compensa- tory gain upon entering the feedyard. After calving in late winter, the combination of lactation and growth/development facilitated a negative energy balance. Thus, the increased plane of nutrition and early weaning of calves resulted in a faster than normal rate of gain. Overall dams consumed 14.9 ± 1.9 kg • d−1 of dry matter (DM), and G:F was 0.120 ± 0.023, but Table 5. Summary statistics (mean ± SD) for performance of early weaned calves managed in the AHNC system by cohort and overall Parameter Cohort 1 Cohort 2 Cohort 3 Cohort 4 Cohort 5 Overall Birth weight, kg 33 ± 3 34 ± 4 33 ± 4 32 ± 6 35 ± 6 33 ± 5 Age at weaning, d 108 ± 20 120 ± 21 101 ± 21 97 ± 18 100 ± 19 105 ± 21 Preweaning ADG, kg • d−1 0.48 ± 0.06 0.38 ± 0.04 0.36 ± 0.08 0.40 ± 0.06 0.36 ± 0.09 0.40 ± 0.08 Weaning weight, kg 147 ± 24 133 ± 25 111 ± 26 118 ± 22 115 ± 28 125 ± 28 Postweaning ADGa, kg • d−1 0.8 ± 0.2 1.0 ± 0.3 0.9 ± 0.3 1.1 ± 0.2 1.2 ± 0.4 0.9 ± 0.3 Postweaning dry lot period, d 43 40 55 61 58 51 ± 9 Female calves weaned, % 58.8 57.1 53.7 67.9 67.9 61.1 ± 6.5 aDry lot phase. D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 10 Harrison et al. Translate basic science to industry innovation G:F continued to improve in later cohorts (Table 6). Although dams in the current study were able to gain weight rapidly, their conversion of feed to BW was poor. There was a numerical reduction in G:F for cohort 4 when compared to other cohorts, espe- cially other sustaining cohorts (e.g., cohorts 3 and 5; Table 6). In cohort 4, fence-line weaning was un- successful, and half of the dams were still lactating up to a few weeks prior to harvest. Increased energy requirements of lactation likely contributed to the decreased feed efficiency in cohort 4 (Ferrell and Jenkins, 1985; Nkrumah et al., 2006). Kansas State Research and Extension (2017) reported average G:F of 0.159 for conventionally raised and finished heifers. Wertz et al. (2002) ana- lyzed the feed efficiency of conventionally raised and finished 2 yr-old Angus heifers and determined a G:F of 0.132. The G:F of AHNC females was reduced when compared to their nulliparous con- temporaries. It was assumed that the reduced effi- ciency was due to recent parturition and lactation (e.g., presence of mammary tissue). Additionally, reduced feed efficiency is often associated with heavy animals at the start of the finishing period (Nkrumah et  al., 2006). Although the feed effi- ciency of AHNC dams was poorer than conven- tionally raised and finished heifers, AHNC dams received the finishing ration a fewer number of days than animals in conventional finishing sys- tems. Additionally, the elimination of the highly in- efficient mature cowherd may offset decreased feed efficiency during the short finishing phase. While in the FIU, dams in cohorts 1 and 2 con- sumed 15.6 ± 1.6 and 13.9 ± 1.9 kg • d−1 of DM, re- spectively. The five-cohort DMI average was within the range of the two DMI measurements obtained from robust feed intake measurements. The ADG for the period was 1.9 ± 0.5 and 1.7 ± 0.5 kg • d−1 for cohorts 1 and 2, respectively. These values were similar to the five-cohort ADG (Table 6), indicat- ing that ADG remained relatively consistent across all five cohorts. Gain:feed calculated for time in the FIU was 0.112 ± 0.294 and 0.116 ± 0.357 for co- horts 1 and 2, respectively. The increased DMI and less desirable G:F for cohort 1 was likely due to a heavier BW at the beginning of the feeding period than dams in cohort 2. Dams in the current study gained rapidly in the feedyard but were slightly less efficient than conventionally raised and finished heifers (Kansas State Research and Extension, 2017). Carcass Performance Table  7 includes carcass characteristics of the 222 AHNC females that were harvested. For co- horts 3–5, age at harvest was 904 ± 20 d (i.e., under 30 mo of age based on documented chronological age). The packing plant did not use birthdates to determine chronological age but used dentition as a surrogate criterion to determine chronological age. Dams with three or more permanent incisors were declared over 30 mo of age. Dentition classi- fied 68.3% of carcasses as over 30 mo of age. This is an important consideration for an AHNC pro- ducer, as carcasses declared over 30 mo of age will receive a sizeable discount (e.g., $100 per carcass in the current study) in addition to any discounts for advanced ossification that is assessed by the USDA grader. In the current study, only 29.5% of carcasses exceeded 30 mo of age based on docu- mented birthdates for cohorts 3–5, indicating that dentition was a crude measure of chronological age (Shorthose et  al., 1990; Schönfeldt and Strydom, 2011). However, recent changes to the USDA grading system allows producers to provide third- party age and source verification of cattle, which overrides dentition scores and would help mitigate discounts for carcasses declared over 30 mo of age based on dentition. Overall, the five cohorts had an HCW of 367  ± 35  kg and dressing percentage of 59.8% ± 1.9% (Table 7). Finding an industry average for the dressing percentage of similar cattle was difficult, Table 6. Summary statistics (mean ± SD) for finishing performance of AHNC primiparous females by co- hort and overall Parameter Cohort 1 Cohort 2 Cohort 3 Cohort 4a Cohort 5 Overall Entry BW, kg 518 ± 49 453 ± 41 481 ± 45 421 ± 40 451 ± 50 464 ± 54 Exit BW, kg 664 ± 55 620 ± 64 626 ± 50 645 ± 55 631 ± 52 637 ± 57 ADGb, kg • d−1 1.6 ± 0.3 1.8 ± 0.4 1.9 ± 0.3 1.9 ± 0.3 2.0 ± 0.4 1.9 ± 0.4 DMI b, kg • d−1 14.3 ± 1.3 14.6 ± 1.7 14.1 ± 1.2 17.5 ± 1.4 14.0 ± 1.0 14.9 ± 1.9 Gain:feedb 0.112 ± 0.022 0.123 ± 0.023 0.133 ± 0.019 0.109 ± 0.016 0.123 ± 0.025 0.120 ± 0.023 aWeaning time was unintentionally delayed in over half of the dams in this cohort. bADG, daily DMI, and gain:feed were calculated for time on the finishing ration. D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 11Evaluation of an All Heifer, No Cow beef herd Translate basic science to industry innovation but generally 62% is used as an industry benchmark for dressing percentage, considering both conven- tionally raised and finished steers and heifers (Nold, 2013; Content, 2018). Decreased dressing percent- ages observed in the current study were likely due to increased reproductive and mammary tissue associ- ated with calving and lactation and an increased age at harvest (Waggoner et al., 1990; Pritchard and Berg, 1993; Nkrumah et al., 2006; Nogalski et al., 2016). Dressing percentages of females in the current study exceeded dressing percentages reported for OCF in the literature. Nogalski et  al. (2016) harvested maiden heifers at 18 mo after being conventionally raised and finished and OCF that were subsequently finished and harvested at 28 mo of age. The OCF had heavier live BW at harvest (570  ± 17  kg) but decreased dressing percentage (54.5% ± 0.4%) when compared to the maiden heifers (BW = 482 ± 13 kg; dressing percent = 57.1% ± 0.3%; Nogalski et  al., 2016). Additional comparisons of OCF carcasses to conventionally raised and finished carcasses have also reported decreased yields for OCF (Joseph and Crowley, 1971; Boucqué et  al., 1980). Hot carcass weights of AHNC dams in the current study were only slightly lower than HCW of conventionally raised and finished steers and heifers (394  kg) re- ported in the 2016 National Fed Beef Quality Audit (NCBA, 2017). In the current study, all carcasses were sold on a value-based grid, in which YG and QG were im- portant attributes. Yield grade-related attributes are included in Table  8. Across the five cohorts, USDA YG was 2.6 ± 0.7 and calculated YG was 2.9 ± 0.7. A comparison of USDA YG and calcu- lated YG showed that mean USDA YG was less (P  =  0.001) than calculated YG. This difference was expected considering USDA yield grading does not use standard rounding rules (i.e., YG 2.6 is classified as a YG 2, not a YG 3). Overall, REA measured 88.2 ± 11.0 cm2, back fat thickness meas- ured 1.20 ± 0.37 cm, and KPH was 1.96% ± 0.38% (Table 8). Based on results from the 2016 National Fed Beef Quality Audit, mean REA was 83.2 cm2 and mean back fat thickness was 1.42 cm (NCBA, 2017). Carcasses in the current study were leaner than conventionally raised and finished steers and heifers based on the objective measures of REA and back fat thickness. Performance of these Table 7. Summary statistics (mean ± SD) for general characteristics of AHNC primiparous females and carcasses at harvest by cohort and overall Parameter Cohort 1 Cohort 2 Cohort 3 Cohort 4 Cohort 5 Overall Females harvested, n 43 43 46 44 46 222 Age at harvesta, d – – 898 ± 14 919 ± 16 895 ± 20 904 ± 20 Shrunk BWb, kg 638 ± 53 596 ± 62 602 ± 48 620 ± 53 607 ± 50 613 ± 55 HCW, kg 389 ± 33 366 ± 36.3 351 ± 28.1 372 ± 31.7 358 ± 32.1 367 ± 35 Dressing percentage, % 61.0 ± 1.5 61.0 ± 2.0 58.3 ± 1.6 59.8 ± 1.2 59.0 ± 1.6 59.8 ± 1.9 Carcasses classified over 30 mo of agec,d, % 71.4 69.8 63.0 75.0 63.0 68.3 ± 5.3 aUnable to calculate for cohorts 1 and 2 since birthdates were unknown. bLive shrunk BW using 4% pencil shrink. cAssessed via dentition by the packer; carcasses with three or more permanent incisors were declared over 30 mo of age. dBased on documented birthdates for cohorts 3 through 5, only 29.5% of carcasses were over 30 mo of age at harvest. Table 8. Summary statistics (mean ± SD) for YG-related attributes of carcasses from AHNC primiparous females and percentages of carcasses in each USDA YG category by cohort and overall Parameter Cohort 1 Cohort 2 Cohort 3 Cohort 4 Cohort 5 Overall Ribeye area, sq. cm. 89.8 ± 11.7 86.9 ± 9.6 80.5 ± 6.7 90.3 ± 11.9 91.9 ± 4.7 88.2 ± 11.0 Calculated YG 2.9 ± 0.7 2.9 ± 0.8 3.2 ± 0.5 2.8 ± 0.7 2.5 ± 0.7 2.9 ± 0.7 Kidney pelvic heart fat, % 1.62 ± 0.29 2.00 ± 0.45 2.12 ± 0.26 1.85 ± 0.29 2.20 ± 0.27 1.96 ± 0.38 Back fat thicknessa, cm 1.30 ± 0.25 1.21 ± 0.42 1.26 ± 0.30 1.29 ± 0.39 0.97 ± 0.36 1.20 ± 0.37 USDA YG 2.3 ± 0.8 2.6 ± 0.8 2.5 ± 0.6 2.9 ± 0.6 2.6 ± 0.7 2.6 ± 0.7 USDA YG 1, % 16.7 4.7 2.2 0.0 2.2 5.2 ± 6.7 USDA YG 2, % 33.3 39.5 47.8 22.7 44.4 37.5 ± 9.9 USDA YG 3, % 50.0 48.8 50.0 68.2 44.4 52.3 ± 9.2 USDA YG 4, % 0.0 4.7 0.0 4.5 8.9 3.6 ± 3.7 USDA YG 5, % 0.0 2.3 0.0 2.3 0.0 0.9 ± 1.3 aMeasured at a point three-fourths of the distance of the outer length of the ribeye (USDA, 2018). D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 12 Harrison et al. Translate basic science to industry innovation carcasses resembled carcass performance from fe- males managed in an integrated system where heif- ers were bred young, calves were early weaned, and dams were finished and slaughtered at 24 mo of age (Riggs, 2001). Integrated system females (n  =  22) had similar HCW (361  ± 28  kg), dressing per- centage (60.0% ± 2.2%), and USDA YG (3.1 ± 0.7) to females in the current study (Riggs, 2001). The distribution of USDA YG assigned to AHNC carcasses closely resembled the YG dis- tribution for conventionally raised and finished beef cattle (NCBA, 2017). The authors reported 9.5%, 36.5%, 39.4%, 12.1%, and 2.5% of carcasses graded YG 1, YG 2, YG 3, YG 4, and YG 5, re- spectively (NCBA, 2017). Table  7 shows percent- ages of AHNC carcasses that were represented in the five YG categories. In the current study, the pre- dominant USDA YG was 3 and included 52.3% ± 9.2% of all graded carcasses. In the current study, YG 4 and 5 only represented 3.6% ± 3.7% and 0.9% ± 1.3% of total harvested carcasses, respectively (Table 8). Based on carcass maturity, the USDA grader classified 20.5% ± 18.7% of carcasses as mature and the remaining were classified as youthful (Table 9). Mean LM for AHNC carcasses was 166 ± 26 and BM was 236 ± 81 for youthful and mature carcasses combined (Table 8). It is important to note in cohort 3 that there were no C maturity carcasses. Females in cohort 3 did not receive an estrogenic implant during the feedyard phase, likely contributing to the absence of mature carcasses as it has been demon- strated that estrogenic implants increase the rate of skeletal ossification in beef carcasses (Grumbach and Auchus, 1999; Tatum, 2011). When calculating OM, BM is more influential than LM. Overall ma- turity score was 213 ± 54, which coincides with B maturity (Table 9). The young age of these females coupled with accelerated levels of ossification sup- ported the theory that hormones associated with pregnancy, calving, and lactation cause accel- erated bone ossification (Waggoner et  al., 1990; Kreikemeier and Unruh, 1993; Field et al., 1996). Waggoner et  al. (1990) reported similar mean (±SD) maturity scores for OCF: LM  =  180  ± 3, BM = 216 ± 4, and OM = 205 ± 3. Mean (±SD) MA of AHNC carcasses was 457 ± 87 and corresponded with a marbling level of small57 (Table 9). The 2016 National Fed Beef Quality Audit reported an average MA of small70 for conventionally raised and finished steers and heifers (NCBA, 2017). Reiling et  al. (1995) and Shackelford et  al. (1995) reported MA of small75 and small27 for conventionally raised and finished heifers and OCF, respectively. Marbling scores of AHNC carcasses in the current study were within the range of MA previously reported for beef pro- duced by OCF and only slightly less than scores reported for conventionally raised and finished steers and heifers (Reiling et al., 1995; Shackelford et  al., 1995; Nogalski et  al., 2016; NCBA, 2017). Carcasses produced by AHNC females were able to sufficiently marble, but advanced carcass maturity is penalized carcasses when QG was assigned. Overall, 62.4% ± 29.1% of carcasses were classified as USDA Choice by USDA grading Table 9. Summary statistics (mean ± SD) for QG-related attributes of carcasses from AHNC primiparous females and percentages of carcasses in each USDA QG category by cohort and overall Parameter Cohort 1 Cohort 2 Cohort 3 Cohort 4 Cohort 5 Overall MAa 475 ± 75.7 430 ± 85.8 490 ± 89.4 428 ± 95.3 460 ± 71.8 457 ± 87.1 Lean maturity scoreb 170 ± 14.1 161 ± 37.1 173 ± 13.0 155 ± 20.7 170 ± 32.1 166 ± 26.0 Bone maturity scoreb 281 ± 55.5 229 ± 101.7 215 ± 31.3 245 ± 110.8 213 ± 60.7 236 ± 80.7 Overall maturity scoreb 249 ± 40.8 213 ± 75.8 201 ± 22.4 205 ± 56.2 202 ± 47.5 213 ± 53.9 C maturity carcassesc, % 47.6 27.9 0.0 20.5 6.7 20.5 ± 18.7 Calculated C maturity carcassesd, % 35.7 32.6 0 13.6 13.3 19.0 ± 14.9 USDA Choice and greater, % 42.9 25.6 97.8 63.6 82.2 62.4 ± 29.1 USDA Prime, % 0.0 0.0 6.5 4.6 13.3 4.9 ± 5.5 USDA Certified Angus Beef, % 0.0 2.3 6.5 4.6 22.2 7.1 ± 8.8 USDA Choice, % 42.9 23.3 84.8 54.6 46.7 50.5 ± 22.4 USDA Select, % 9.5 32.6 2.2 15.9 11.1 14.3 ± 11.4 Othere, % 47.6 41.9 0.0 20.5 6.7 23.3 ± 21.0 aMA (slight00 = 300, small00 = 400, modest00 = 500, etc.). bMaturity score (A00 = 100, B00 = 200, C00 = 300, etc.). cCarcasses classified as C maturity by the USDA grader. dCarcasses classified as C maturity based on overall maturity calculated by Colorado State University. eOther included: Standard, Commercial, Utility, dark cutter, blood splash, and advanced bone maturity. D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 13Evaluation of an All Heifer, No Cow beef herd Translate basic science to industry innovation personnel (Table  9). This was only slightly less than the percentage of USDA Choice carcasses (68.8%) reported in the 2016 National Fed Beef Quality Audit (NCBA, 2017). The large amount of variation in the percentage of USDA Choice car- casses was due to the advanced maturity of some carcasses, which caused carcasses to not be graded and receive carcass discounts. There were espe- cially large numbers of ungraded carcasses in co- horts 1 and 2 due to their unknown age (Table 9). In cohorts 3 through 5, QG greatly improved with 110/136 grading USDA Choice or better. The in- tegrated system studied by Riggs (2001) resulted in 68.2% of carcasses grading USDA Choice. In the current study, 4.9 ± 5.5% of all carcasses were USDA Prime (Table  8). On average, only 4.6% of conventionally raised and finished carcasses graded USDA Prime (NCBA, 2017). However, the percentages of ungraded carcasses in the current study (23.3% ± 21.0%) greatly exceeded that of conventionally raised and finished carcasses (3.6%; NCBA, 2017). Carcasses that were ungraded in the current study were mostly ineligible for grading due to advanced bone ossification. However, recent changes to the USDA grading rules require that if the carcass is declared under 30 mo of age on the harvest floor by either dentition or third-party age and source verification, the USDA must use that as the maturity determinant in the QG instead of physiological carcass maturity. Thus, with third- party age and source verification and harvesting females at less than 30 mo of age, discounts for carcasses over 30 mo of age and advanced physio- logical maturity could be avoided and overall prof- itability could be increased. Table 10 presents mean (±SD) tenderness and cooking measurements for cohorts 1 and 2.  Slice shear force values were 25.2 ± 6.2 and 27.0 ± 10.7 kg, WBSF values were 4.9 ± 0.9 and 5.0 ± 1.2 kg, and CL estimates were 25.8 ± 3.7 and 26.5 ± 4.3 for co- horts 1 and 2, respectively. Huffman et  al. (1996) noted that a WBSF value of 4.1 kg would result in a 98% consumer acceptability rating. Furthermore, a wide range of WBSF values has been reported for beef produced by primiparous females, with values ranging from 3.6 to 9.8 (Waggoner et  al., 1990; Shackelford et  al., 1995; Field et  al., 1996, 1997). Field and colleagues (1997) examined differences between A and C maturity carcasses produced by finished beef females of similar chronological age (i.e., both groups consisted of heifers 31 to 35 mo of age) and determined that there were no differ- ences between mature collagen crosslinks or steak tenderness. The authors concluded that collagen maturation was independent of skeletal matur- ation (Field et al., 1997). Current research has not yet demonstrated a significant correlation between meat tenderness and carcass maturity (Tatum, 2011; Acheson et al., 2014, Semler et al., 2016). In this study, even though birthdates were un- known for cohorts 1 and 2, it was very unlikely that any harvested females exceeded 42 mo of age at harvest (i.e., OM = C or greater). Overall, 177 carcasses were classified as youthful and 43 were classified as mature based on carcass maturity that was assessed by USDA grading personnel. There were no differences between maturity groups for REA (P  =  0.13), USDA YG (P  =  0.67), MA (P = 0.26), or LM (P = 1.00). Mature carcasses had greater BM (P < 0.001) and OM (P < 0.001) when compared to youthful carcasses (Table  10). These results were expected since BM is the major de- terminant of OM (Hale et al., 2013). The mature group had greater (P  <  0.01) HCW and greater (P < 0.001) dressing percentages. Increased HCW for the mature group was likely due to increased age at harvest. The reduced dressing percentage for Table 10. Comparison (mean ± SD) of key carcass attributes between A and B maturity carcasses vs. C maturity carcasses produced from AHNC prim- iparous females across five cohorts Parameter Overall maturity P > |t|A and B maturity C maturitya Carcasses, n 177 43 – HCW, kg 363 ± 32 383 ± 39 <0.01 Dressing percentage, % 58.4 ± 2.9 60.6 ± 2.2 <0.001 Ribeye area, cm2 87.74 ± 10.3 90.1 ± 13.2 0.13 USDA YG 2.6 ± 0.7 2.5 ± 0.8 0.67 MAb 459 ± 89 450 ± 76 0.25 Lean maturity scorec 166 ± 26 166 ± 25 0.99 Bone maturity scorec 213 ± 68 330 ± 62 <0.001 Overall maturity scorec,d 197 ± 43 283 ± 39d <0.001 Age at harveste, d 902 ± 20 919 ± 11 <0.001 Slice shear forcef, kg 25.4 ± 8.6 27.6 ± 9.1 0.29 WBSFf, kg 4.9 ± 1.2 5.0 ± 0.8 0.96 Cooking lossf, % 25.4 ± 4.1 26.1 ± 4.2 0.47 aC maturity carcasses classified by USDA grader. bMA (slight00 = 300, small00 = 400, modest00 = 500, etc.). cMaturity score (A00 = 100, B00 = 200, C00 = 300, etc.). dAverage overall maturity score for the C maturity group was not over 300 because the number over C maturity was classified by the USDA grader, but Colorado State University took the bone measure- ments and determined some of the carcasses classified as C maturity were B maturity. eAge at harvest was only evaluated for cohorts 3 through 5 since birth dates were unknown for cohorts 1 and 2. fComparisons were only made on cohorts 1 and 2: youthful car- casses (n = 28) and mature carcasses (n = 57). D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 14 Harrison et al. Translate basic science to industry innovation youthful carcasses was surprising because, gener- ally, older animals have decreased dressing percent- ages (Content, 2018). However, decreased dressing percentages in the youthful group were likely due to a small number of animals not reaching target har- vest BW. For cohorts 3 through 5, mature carcasses (n = 12; 919 ± 11 d) were older (P = 0.001) than youthful carcasses (n = 120; 903 ± 20 d) at harvest (Table 10). Differences in meat tenderness between youthful (n = 28) and mature (n = 57) carcasses were compared using data collected on cohorts 1 and 2. There were no differences (P = 0.29; P = 0.96; P = 0.47) between youthful and mature carcasses for SSF, WBSF, and CL, respectively (Table  10). Based on the objective value of meat tenderness, there were no differences between youthful and ad- vanced carcass maturities. Field et al. (1997) compared A and C maturity carcasses produced by grain-finished OCF that were harvested at 32.5 mo of age and found no differences in comparisons of LM, MA, WBSF, and muscle collagen concentration between ma- turity groups. However, there were differences in BM across maturity groups (Field et  al., 1997). A  comparison of maiden yearling, 2-yr-old, and once-calved females showed that OCF had greater BM than maiden heifers, but MA was the same across all groups (Waggoner et  al., 1990). Sensory panelists and WBSF values indicated that beef produced by OCF was similar in tender- ness to beef produced by maiden 2-yr-old heifers but tougher than beef produced by maiden year- ling heifers (Waggoner et  al., 1990). Joseph and Crowley (1971) compared beef from 12 maiden and 24 Hereford OCF that were harvested at 27 to 30 mo of age in a taste panel and found no differences between the two groups (Joseph and Crowley, 1971). These results indicated that the AHNC beef production system is a viable system for producing beef. Carcasses produced by AHNC females are of similar quality to carcasses produced by con- ventionally raised and finished steers and heifers. With exceptions of BM and OM, beef produced by youthful AHNC carcasses was the same quality as beef produced by mature carcasses based on car- cass maturity. Comparison of Cohorts Seidel and Whittier (2015) hypothesized that the AHNC beef production system would not reach equilibrium until later cohorts due to the in- fluence of purchased heifers with little background information decreasing the performance of initial cohorts. Thus, it was anticipated that the perform- ance of sustaining cohorts would exceed the per- formance of initial cohorts. However, results of regression analyses yielded conflicting results. As shown in Table 12, mean 30-d pregnancy rates were 47.1% and 55.6% for initial and sustaining cohorts, respectively. At the 140-d pregnancy diagnosis, 94.1% and 92.6% of heifers were pregnant in initial and sustaining cohorts, respectively. There were no differences in 30-d (P = 0.17) and 140-d (P = 0.48) pregnancy rates between initial and sustaining co- horts (Table 11). Table 12 summarizes differences in carcass and growth performance for initial and sustaining co- horts. Analyses showed that ADG (P = 0.88), YG (P = 0.25), and MA (P = 0.44) did not differ be- tween cohorts. However, females in sustaining cohorts consumed more (P < 0.001) feed than fe- males in initial cohorts, but carcasses in initial co- horts had heavier (P < 0.001) HCW and improved (P  <  0.001) dressing percentages when compared to carcasses in the sustaining cohorts. These results were somewhat surprising; however, increased DMI for sustaining cohorts was likely due to females in cohort 4 lactating longer than females in other co- horts. Carcasses produced by the initial cohorts had more advanced BM (P < 0.01) and OM (P < 0.05), indicating, based on estimates of carcass maturity, that females in cohorts 1 and 2 were older at harvest (Table 12). Performance of initial cohorts was only slightly decreased, suggesting that producers could easily enter and exit the AHNC beef production system without compromised performance. Over 30 yr ago, several studies evaluated sin- gle-calf heifer beef production. At the time, the con- sensus based on theoretical simulations was that the system was the most efficient means of producing Table 11.  Comparison of reproductive perform- ance between initial and sustaining cohorts of the AHNC beef production systema Parameter Initial cohortsb Sustaining cohortsc SE P > |t| Females, n 102 162 – – Pregnant 30 d after fixed time artificial insemin- ation, % 47.1 55.6 26.2 0.17 Pregnant 140 d after fixed time artificial insemin- ation, % 94.1 92.6 52.5 0.48 aAnimals with missing data were omitted from analyses. bCohorts 1 and 2. cCohorts 3 through 5. D ow nloaded from https://academ ic.oup.com /tas/article/4/4/txaa191/5940757 by guest on 15 June 2023 15Evaluation of an All Heifer, No Cow beef herd Translate basic science to industry innovation beef (Taylor et al., 1985; Sell et al., 1988). The cur- rent study indicated that the AHNC beef produc- tion system can effectively produce female calves for replacements and high-quality carcasses at harvest. The AHNC beef production system offers flexibility. The AHNC beef production system could be started with calves, yearling heifers, bred heifers, or pairs and, similarly, producers could exit the system by selling yearling heifers, bred heifers, pairs, or cows after calving depending on market conditions and goals of the producer. Further research should be conducted to com- pare the biological and economic efficiency of AHNC beef production to conventional cow-/calf-based beef production. Furthermore, due to age-related and car- cass maturity discounts, the AHNC beef production system warrants evaluation in a grass-based finishing system since grass-finished animals are typically older at harvest and not assigned USDA QG. Another as- pect that merits further evaluation is the potential to accelerate the rates of genetic improvement due to the very short generation interval of heifers that re- place themselves with a heifer. Additionally, this pro- gram would be well suited to a branded beef program where carcass discounts could be avoided and system efficiency could be highlighted. ACKNOWLEDGMENTS The authors thank Select Sires, Inc., for providing sex-selected semen, Colorado State University Experiment Station for financial support, Colorado State University Meat Judging for assist- ance in evaluating carcasses, and Universidad de Costa Rica for assistantship funding. Conflict of interest statement. The authors de- clare no real or perceived conflicts of interest. LITERATURE CITED Acheson, R. J., D. R. Woerner, and J. D. Tatum. 2014. Effects of USDA carcass maturity on sensory attributes of beef produced by grain-finished steers and heifers classified as less than 30 months old using dentition. J. Anim. Sci. 92:1792–1799. doi:10.2527/jas.2013–7553. Arce-Cordero, J.A. 2016. Evaluation of management strategies to improve efficiency and sustainability of beef and dairy cattle operations [MS thesis]. 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Table 12. Comparison of growth and carcass per- formance between initial and sustaining cohorts of the AHNC beef production systema,b Parameter Initial cohortsc Sustaining cohortsd SE P > |t| Carcasses, n 85 135 – – ADG, kg • d−1 1.83 1.83 0.03 0.88 Daily DMI, kg • d−1 14.6 15.1 0.33 <0.001 HCW, kg 385 355 8.41 <0.001 Dressing percentage, % 62.3 58.3 0.31 <0.001 USDA YG 2.5 2.6 0.09 0.25 MAe 451 460 12.60 0.44 Lean maturity scoref 159 164 3.07 <0.01 Bone maturity scoref 230 239 3.35 <0.01 Overall maturity scoref 218 213 2.42 <0.05 aAnimals with missing data were omitted from analyses. bLeast squares means are reported. cCohorts 1 and 2. dCohorts 3 through 5. eMA (slight00 = 300, small00 = 400, modest00 = 500, etc.). fMaturity score (A00 = 100, B00 = 200, C00 = 300, etc.) assessed by carcass maturity. 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