Effects of post-weaning growth rate and puberty induction protocol on reproductive performance of Bos indicus-influenced beef heifers
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A 3-yr study evaluated the effectiveness of puberty induction using exogenous reproductive hormones in beef heifers undergoing different post-weaning growth rates. On d 0 of each year, grazing Angus × Brahman heifers (60 heifers/yr) were stratified by initial BW and age (BW = 253 ± 30 kg; age = 310 ± 18 d), and randomly assigned, in a 3 × 2 factorial design, to achieve a low (LOW; 0.45 kg/d), medium (MED; 0.73 kg/d), or high (HIGH; 1.00 kg/d) growth rate from d 0 to 168 (5 heifers/pasture; 4 pastures/growth rate/yr). Dietary supplements were offered 3 times weekly (Mondays, Wednesdays, and Fridays) at 0800 h to provide 1.8, 2.9, and 4.4 kg of supplement DM per heifer daily from d 0 to 168. On d 0 of each year, 2 pastures/growth rate treatment were randomly assigned to receive (SYNC) or not (NOSYNC) a puberty induction protocol, which consisted of intravaginal controlled internal drug release (CIDR) insertion on d 65, CIDR removal on d 72, followed by 100-µg i.m. injection of GnRH on d 74, and 25-mg i.m. injection of PGF on d 84. Immediately after the puberty induction protocol, all heifers were grouped by growth rate treatment (1 group/growth rate/yr) into a single pasture and exposed to yearling Angus × Brahman bulls from d 84 to 168 (1 bull/group/yr). Interactions among growth rate and puberty induction protocol were not detected for any variable ( ≥ 0.26). Overall heifer ADG achieved only 51 to 56% of targeted ADG, and percentage of mature BW on d 84 did not differ between MED and HIGH heifers ( = 0.30), but both were heavier than LOW heifers ( < 0.01). Percentage of pubertal heifers on d 84 was greater for MED and HIGH vs. LOW heifers ( ≤ 0.05), whereas puberty induction protocol increased puberty attainment on d 84 ( < 0.01). Overall pregnancy and calving percentages after first breeding season were not affected by growth rate or puberty induction protocol ( ≥ 0.25). However, heifers calved 11 d earlier when enrolled in the puberty induction protocol ( = 0.02). In summary, puberty induction and HIGH and MED growth rates resulted in earlier attainment of puberty and pregnancy in -influenced beef heifers. However, neither growth rate or puberty induction impacted overall heifer pregnancy and calving rates on their first breeding season.
author list (cited authors)
Moriel, P., Lancaster, P., Lamb, G. C., Vendramini, J., & Arthington, J. D.