EFFECT OF PRENATAL ANDROGENIZATION ON PERFORMANCE, LACTATION, CARCASS, AND SENSORY TRAITS OF HEIFERS IN A SINGLE-CALF HEIFER SYSTEM

Twenty-four prenatally androgenized (PA) heifers, born to testosterone propionate-implanted cows, and 27 control (C) heifers, born to nonimplanted cows, were bred, calved, and placed in drylot pens, with calf at side, to assess the effects of PA on feedlot growth and lactational performance of heifers used in a single-calf heifer (SCH) system. Lactating heifers were fed an 85% concentrate diet, calves weaned at 117 d postpartum, and heifers slaughtered at a constant compositional end point of 1.1 cm of s.c. fat. Preweaning, PA heifers gained 22.5% faster (P < .01) and were 17.3% more efficient (P < .01) than controls. Prenatal androgenization of the heifer, however, did not affect calf growth performance. All calves gained more than 1.4 kg/d and had an average weaning weight of 159 kg at 117 d of age. Combining heifer-calf weights, PA and C pairs gained 2.88 and 2.53 kg/d, respectively. Correcting for DMI of calves, PA improved (P < .01) efficiency of beef production 10.8%. Four percent fat-corrected milk yield of PA and C heifers averaged 7.96 and 7.60 kg/d, respectively, and the percentage of milk protein and fat did not differ. Accounting for average BW, milk production, and DMI, PA and C lactating heifers should have gained 1.27 kg/d; however, gains were 137 and 127% of those predicted, respectively. Overall, pre- and postweaning, PA heifers required 10 fewer (P < .04) days on feed, gained 23% faster (P < .01), and were 16% more efficient (P < .02) than C heifers. At slaughter, PA and C heifers averaged 853 and 865 d of age, respectively. Bone and lean maturity scores averaged B-0 and A(60), respectively, although one carcass was classified as mature (C-maturity). Marbling scores exceeded Small(50), and sensory traits did not differ. Thus, PA enhanced growth and efficiency of beef production from heifers used in a SCH system but did not affect lactational or carcass traits.