Effect of bulls on pregnancy rate of estrous synchronized Brangus cows

Abstract

The objective of this research was to investigate the effect of bulls on pregnancy rate of estrous synchronized Brangus cows. Seven Brangus bulls with average body weight of 820 kg and aged approximately five years were used in this study. A total of thirty five cows were divided into seven groups, each consisted of five cows were also used. All animals were raised in semilar grazing system and fed with approximately 5 and 2 kg/head/day of concentrates for bulls and cows, respectively. Estrous synchronization was carried out using controlled internal drug releasing devise (CIDR) containing 1.38 mg progesterone for eight days. All cows were given 2 mg oestradiol benzoate, intramuscularly during the day of CIDR insertion(day 0). The CIDR was removel after 8 days and 125 µg prostaglandin injected was intramuscularly. One day after the removal of CIDR to all cows were given 1 mg of oestradiol benzoate. Cows were observed visually for oestrus at 06.00- 08.00 am, 12.00-14.00, and 16.00 -18.00 pm (on the day 10) respectively. Characterization of the oestrus response was defined as cows receiving 1-3 mounts during mixing together bull and cows. All cows were mixed with bulls with 1: 5 ratio of bull : cows for seven day. All animals were kept in a pasture herd on a separate two hectare paddock for each group. Thirty two days after mixing, pregnancy was determined using transrectal ultrasonography. The result indicated that the conception rate (CR) varied from 0.0 - 60.0 %.