Impact of heifer development system on subsequent ADG and reproduction in two different breeding seasons

Abstract Text: The objective of this study was to determine the impact of heifer development system on subsequent growth and reproductive performance in two breeding seasons. In Exp. 1, over a 3 yr period, 196 May-born crossbred (5/8 Red Angus, 3/8 Continental) heifers were stratified by BW and randomly assigned to 1 of 2 post-weaning nutritional treatments (2 pastures·treatment^-1·year^-1) beginning mid-January to mid-April. Heifers were offered ad libitum meadow hay (HAY) and 1.81 kg/d (29% CP, DM basis) supplement or allowed to graze meadow (MDW) and 0.45 kg/d supplement. Heifers were managed as a single herd prior to and following treatment. Heifers were synchronized with a single PGF_2α injection 5 d after being placed with bulls for 45 d. Heifers on HAY treatment had greater (P < 0.01) ADG during the treatment period compared with MDW heifers (0.63 ± 0.01 kg/d vs. 0.33 ± 0.01 kg/d, respectively). However, heifers grazing meadow experienced a compensatory gain resulting in similar (P ≥ 0.12) BW in June, July, and at pregnancy diagnosis. There was no difference (P = 0.65) in the proportion of heifers attaining puberty prior to the breeding season for HAY (62 ± 18%) and MDW (49 ± 18%) heifers. Pregnancy rates were similar (P = 0.79) between HAY vs. MDW treatments (69 ± 6% vs. 67 ± 6% respectively). In Exp. 2, 100 spring-born, crossbred (5/8 Red Angus, 3/8 Continental) heifers were, over 2 yr, stratified by BW and randomly assigned to HAY or MDW treatments. Similar to Exp. 1, HAY heifers had greater (P < 0.01) ADG during the treatment period than MDW heifers (0.80 ± 0.02 vs. 0.47 ± 0.02 kg/d). During the spring, HAY and MDW heifers had similar (P = 0.14) ADG and BW was similar (P ≥ 0.17) in May and September. Pubertal status prior to breeding was not affected by treatment (P = 0.55). Pregnancy rates were similar for HAY (88 ± 5%) and MDW (86 ± 5%, P = 0.78) heifers. Although ADG during the winter feeding period was greater for HAY heifers, BW was similar in the spring, summer, and at pregnancy diagnosis between treatments suggesting a compensatory growth effect for MDW heifers. Similarly, there was no difference in pubertal status or pregnancy rate indicating that a lower input winter management system is viable to maintain heifer pubertal status and pregnancy rates in two breeding seasons.

Keywords: beef heifers, development system, reproduction