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

Abstract

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 1.1cm s.c. fat cover over the 12th and 13th ribs. Heifers were slaughtered 12h 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).