FR 18. Fourty five day breeding season. II: Reproductive performance of first-calf cows

Abstract

This research was performed at Santa Rosa ranch located in the humid tropic in the southwest region of Táchira State, Venezuela, with Brahman heifers kept on pasture, supplemented with minerals and submitted to 45-days-breeding season beginning on march the first (E) vs conventional 90-days starting on april the first (C), to evaluate the reproductive performance of first-calf heifers by pregnancy rate (PP, n=218) and conception date estimated as a day-deviation from breeding from the first day breeding season (FC, n=132). Least-squares analysis of variance was performed on traits including the following effects: Treatments (T:E,C), year of mating (A:1985, 86, ..., 92), and linear regressions of heifer’s weight at mating (WM) and calving date (FP). Adjusted means for PP and FC were 58.7 ± 3.3% and 36.7 ± 2.3 days. PP was affected by T and FP (P<.01) and WM (P<.05) while FC was affected solely by T (P<.01). E was 49.8 and 99.6 % more efficient. PP decreased from 76.7 % for heifers that calved prior to january the first to 33.2 % for those that calved 60 or more days late. The linear regression coefficient of PP on WM was 0.27 %/kg.