103 Puberty induction protocol but not supplement amount overcomes the negative impacts of reduced frequency of supplementation on reproduction of beef heifers

摘要

This study evaluated the performance of Bos indicus-influenced beef heifers submitted to a puberty induction protocol and offered two supplementation amounts and delivery frequencies. Sixty-four Brangus crossbred heifers were stratified by BW and age (244 ± 4 kg; 311 ± 18 d) and assigned into 1 of 16 bahiagrass pastures on d 0. Treatments were randomly assigned to pastures in a 2 × 2 factorial design (4 pastures/treatment) and consisted of soyhulls-based supplementation at 1.25% or 1.75% of BW (DM basis) offered daily or 3 times weekly for 168 d. The puberty induction protocol consisted of CIDR insert on d 56 and removal on d 70, 5-mL PGF2a injection on d 86, 2-mL GnRH injection and timed-AI on d 89. Heifers were exposed to Angus bulls from d 89 to 167 (1 bull/pasture). Pregnancy diagnosis was assessed on d 212. Frequency × rate effects were not detected (P ≥ 0.19) for any variable. Reducing the supplementation frequency from daily to 3X weekly tended (P = 0.07) to decrease overall ADG and puberty attainment on d 56 (53 vs. 41 ± 6%), but not puberty attainment on d 89 (P = 0.45; 84 vs. 78 ± 6%) and pregnancy percentage on d 212 (P = 0.97; 69 vs. 69 ± 7%). Increasing the supplement amount from 1.25% to 1.75% of BW increased (P = 0.04) overall ADG, tended (P = 0.09) to hasten puberty attainment on d 56 (40 vs. 54 ± 6%) and d 89 (74 vs. 88 ± 6%), and enhanced (P = 0.03) pregnancy percentage on d 212 (53 vs. 80 ± 7%). Therefore, the inclusion of a puberty induction protocol, but not increasing the supplement amount, enabled a reduced frequency of supplementation (3 vs. 7 times weekly) without detrimental impacts on percentage of pregnant yearling beef heifers.