1276 Carcass Quality of Primiparous Cows Managed under a Single-Calf Heifer Model Combined with Use of Sexed Semen and Early Weaning

The single-calf heifer model (SCHM) harvests females after early-weaning their first calf, reducing average age and maintenance requirements of the herd, hence increasing biological efficiency of beef production. However, pregnancy estrogens accelerate bone ossification, which might affect carcass value of SCHM females. This study evaluated: overall maturity (OM), bone maturity (BM), lean maturity (LE), marbling (MA), Warner-Bratzler (WBSF) and slice shear force (SSF), and cooking loss (CL) of carcasses of SCHM females. Fifty-three Angus-based yearling heifers (BW = 353 ± 38.8 kg) and a second set of 58 (BW = 307 ± 29.9 kg), were synchronized and inseminated with sexed semen during first and second year of the project, respectively, to calve at approximately 24 mo of age. At weaning, average age of calves was 106 ± 22 and 120 ± 21 d, and first-calf heifers (43 each year) were fed for 88 and 90 d at a feedlot, for years 1 and 2, respectively. At harvest, carcasses were scored for LE, BM, and MA (slight = 300, small = 400, and modest = 500); OM was estimated from BM and LE (A00, B00and C00 maturities corresponded to scores of 100, 200, and 300, respectively). One LM sample was removed for SSF, WBSF and CL measurements. Carcasses were sorted by OM as < 300 or ≥ 300, and the resulting means for carcass traits were compared with a t test. Data were combined across years, since same significant differences (P < 0.05) between OM groups were obtained for both years. Means ± SD for the 66% of the carcasses classified as < 300 OM were: 192 ± 39.3 OM, 211 ± 53 BM, 165 ± 29 LE, 446 ± 84 MA, 25.4 ± 8.6 kg SSF, 4.94 ± 1.19 kg WBSF, and 25.4 ± 4.1% CL. Remaining carcasses ( ≥ 300 OM) were 305 ± 18 OM, 346 ± 46 BM, 167 ± 27 LE, 462 ± 78 MA, 27.6 ± 9.1 kg SSF, 4.96 ± 0.84 kg WBSF, and 26.1 ± 4.2% CL. Significant differences between the 2 OM groups were found for BM (P < 0.001). However, no differences were detected for LE (P = 0.81), MA (P = 0.39), WBSF (P = 0.96), SSF (P = 0.29) or CL (P = 0.47). Therefore, differences in OM and BM did not affect palatability characteristics of carcasses of primiparous SCHM females approximately 30 mo of age.