Average Response to Estrus and Timing of Ovulation in Bos indicus Cattle Synchronized Alternatively with a Synthetic Progestagen

Eighteen multiparous Brahman cows were divided in three groups and synchronized consecutively with a nine-day interval between groups. After implant withdrawal, synchronized cows, together with those forming the sexually active group were subjected to intensive ultrasound exams to detect ovulation. Observation for signs of estrus was continuous and females were classified as a) showing overt signs, defined as those cows that mount and allowed mounting and b) active estrus as females that only mount. Some cows showed estrus with the groups they were synchronized and were classified as being concomitantly in estrus. The total percentage of cows in heat was 66%, of which 83% showed overt signs of estrus and the remaining 16% displayed active estrus. Eight cows were concomitantly in estrus, 75% of them in active estrus and 25% allowing and performing mounting behavior. The expected time of the onset of estrus after implant removal was different among groups (p<0.0004). Ovulation after implant withdrawal occurred in 83% of all animals, although some cows ovulated outside of the range of the group with which they were synchronized. The average time of ovulation after implant removal was similar (p = 0.19), for all groups. Differences were found in the dominant follicular size b etween animals showing overt signs (11.31 2.18 mm) and those displaying active estrus (7.33 1.80 mm) (p<0.01). All the synchronized females displaying overt signs of estrus ovulated contrary to those showing active estrus. Some cows ovulated without manifesting estrous behavior. It is concluded that cows need to display full estrus (mounting and allowed to be mounted) to be considered as candidates for ovulation and the system of synchronizing in alternation but having all the animals together, influences the number of females participating in the sexually active group as the experiment progresses.