A 12-year summary of the effects of estrous synchronization and body weight at breeding on reproductive success of Bos indicus-influenced beef heifers grazing warm-season grasses

Abstract

Objective

The objective was to evaluate the effects of estrus synchronization and body weight before the start of breeding season on reproduction of Bos indicus-influenced beef heifers.

Materials and Methods

Data were collected from grazing, Brangus crossbred beef heifers (n = 594) weaned at 280 ± 26 d of age and fed concentrate from 2 wk after weaning until the end of the breeding season (189 ± 24 d of supplementation). Heifers were initially sorted into those that were (SYNC) and were not (NOSYNC) as- signed to an estrous synchronization protocol before the start of the breeding season. Then, within each synchro- nization group, heifers were sorted into those that were below (BE) or above (AB) 295 kg (65% of mature BW) at the start of the breeding season.

Results and Discussion

Effects of synchronization × BW at breeding and synchronization were not detected for growth performance, but tended to be detected for pu- berty attainment, which was the least for NOSYNC+BE, did not differ between SYNC+BE versus NOSYNC+AB, and was greatest for SYNC+AB heifers. Pregnancy and calving percentages were greater for AB versus BE heifers.

Implications and Applications

Results of this study indicate that Bos indicus-influenced beef heifers need to achieve ≥65% of mature BW at the start of the breeding season to optimize reproduction, whereas estrous synchro- nization protocols enhanced puberty attainment (regard- less of BW) and early calving distribution when heifers were <65% of mature BW at the start of the breeding season.