Reproductive Performance of 2-Year-Old Hereford and Angus Heifers as Influenced by Pre- and Post-Calving Energy Intake

Abstract

The influence of pre- and post-calving energy intake was studied in 203 2-yr.-old heifers (101 Hereford and 102 Angus) nursing their first calves. Two levels of calculated digestible energy (low—8.7 megcal. and high—17.3 megcal.) were fed daily before calving. At calving time, the low group was divided into two groups: a low-moderate (L-M) fed 27.3 megcal. and a low-high (L-H) group fed 48.2 megcal. of digestible energy daily. The high precalving group was divided into three groups at calving time and fed three levels of energy daily: high-low (H-L) 14.2 megcal.; high-moderate (H-M) 27.3 megcal. and high-high (H-H) 48.2 megcal. The heifers were assigned to treatment 135 to 142 days prior to calving and remained on treatment until 120 days after calving. The 60-day breeding season started 60 days after calving. Results show that level of energy intake can markedly alter reproductive performance in 2-yr.-old heifers nursing their first calves. Pregnancy rate 120 days after calving was directly related to the post-calving energy level. Eighty-seven percent of the cows fed the high energy level after calving were pregnant compared with 72% of those fed the moderate level and 64% of those fed the low energy level (0.01<P<0.05). The onset of estrus was delayed in cows receiving the low level of energy before calving. The low pregnancy rate in the cows fed the low energy level after calving occurred because 30% of the Hereford cows and 9% of the Angus cows failed to show estrus (0.01<P<0.05). Copyright © 1969. American Society of Animal Science . Copyright 1969 by American Society of Animal Science