Effects of Prenatal Androgenization and Implantation on the Performance and Carcass Composition of Lactating Heifers in the Single-Calf Heifer System

Two experiments were conducted to evaluate feedlot performance of heifers and calves and the lactational characteristics and carcass composition and quality of heifers while in the single-calf heifer (SCH) system. In Exp. 1, 24 lactating Angus × Holstein heifers were slowly adapted to an 85% concentrate diet, and one-half of the heifers were implanted with Finaplix-H®, both at 11 wk postpartum. Heifer-calf pairs were then placed in feedlot pens, equipped with pinpointer feeding devices, and fed an 85% concentrate diet for 102 d. The control (C) and implanted (I) heifers had similar (P=0.27) daily gains and similar (P=0.30) DMI; however, I heifers consumed 8.9% less (P<0.05) DM as a percentage of BW. Pair efficiency of feed conversion tended to be higher (P<0.09) for I heifers than for C heifers. Hot carcass weight tended to be higher (P<0.10) for the I heifers. Ribeye area was 13% greater (P<0.05) and marbling score was 8.7% lower (P<0.01) for the I heifers than for the C heifers. In Exp. 2, 26 lactating Angus × Simmental heifers were used in the SCH system. Heifer adaptation to a high concentrate diet began 3 to 4 wk prepartum. Two to 3 d postpartum, 16 control (C) and 10 prenatally androgenized (PA) heifer-calf pairs were weighed, and eight C and five PA heifers were implanted with Synovex-H®. They were then placed in feedlot pens equipped with pinpointer feeding devices. By 1 wk postpartum, all heifers were adapted to an 85% concentrate diet and fed until they possessed approximately 1.1 cm s.c. fat cover over the 12th and 13th ribs. Heifers were slaughtered 12 h postweaning. The PA heifers tended to consume more (P<0.11) DM than C heifers. Gain:feed (G:F) was similar (P=0.35) for the C and PA heifers; however, the C heifers tended to have an improved (P<0.08) pair G:F. Heifer G:F and pair G:F were both similar (P=0.53) for the I and nonimplanted heifers. Most carcass measurements were unaffected by treatment; however, the I heifers tended to have higher marbling scores (P<0.07).