| Abstrakt: |
A 4-yr study was conducted to determine the impact of heifer development system on subsequent growth and reproductive performance in 2 breeding seasons. In Exp. 1, March-born, crossbred (5/8 Red Angus, 3/8 Continental; n= 225) heifers were stratified by BW and randomly assigned to 1 of 2 post-weaning nutritional treatments (2 pastures·treatment−1·yr−1) from mid-January to mid-April. Heifers were offered ad libitum meadow hay (HAY) and 1.81 kg/d (29% CP, DM) supplement or allowed to graze meadow (MDW) and offered 0.45 kg/d supplement. Heifers were managed as a single herd before and following treatment. Heifers were synchronized with a single PG injection 5 d after being placed with bulls for a 45 d breeding season. HAY heifers had greater (P= 0.01) ADG during the treatment period than MDW heifers (0.77 vs. 0.51 ± 0.03 kg/d; HAY, MDW). At pregnancy diagnosis, HAY heifers tended to have greater BW compared with MDW heifers (P= 0.06; 377 vs. 367 ± 3 kg; HAY, MDW). Percent of mature BW before the breeding season was greater (P= 0.02) for HAY compared with MDW (58% vs. 55% ± 1%; HAY, MDW). Pregnancy rates were similar for HAY and MDW heifers (P= 0.97, 88 ± 4%). In Exp. 2, May-born, crossbred (5/8 Red Angus, 3/8 Continental; n= 258) heifers were stratified by BW and randomly assigned to HAY or MDW treatments. Similar to Exp. 1, heifers on HAY treatment had greater (P= 0.01) ADG during the treatment period (0.63 vs. 0.39 ± 0.03 kg/d; HAY, MDW), resulting in greater pre-breeding BW (P= 0.02) for HAY heifers compared with MDW heifers (320 vs. 305 ± 3 kg, respectively). At pregnancy diagnosis, BW was similar (P= 0.16) between treatments (368 vs. 356 ± 4 kg; HAY, MDW). Percent of mature BW before the breeding season was greater (P= 0.02) for HAY (58%) compared with MDW (54%). Pregnancy rates were similar (P= 0.44) between treatments (72 vs. 68 ± 4%; HAY, MDW). Heifer development system did not impact pregnancy rate in the March or May replacement heifers; however, March heifer pregnancy rate was greater (P< 0.01) than May (87 vs. 70 ± 3%). The lower pregnancy rate in May heifers may be due to declining forage quality during the breeding season. |
