The reproductive performance of East African (Bos Indicus) Zebu cattle in Ethiopia. 1. Estrous cycle length, duration, behavior and ovulation time.

The average (+/- standard deviation) estrous cycle length of 28 East African Zebu cows over a 217-d period, was 22.6 +/- 6.5 d with no significant (P>0.05) difference between seasons. Estrus had a mean duration of 7.66 +/- 4.68 h (ranging from 1 to 24 h) followed by ovulation 25.82 +/- 5.25 h after the onset of estrus. A larger number of estruses started during the day (64 vs 36% P<0.001) and they were longer during the dry season (P<0.05). Proestrus and metaestrus had average duration of 3.46 +/- 3.57 and 3.65 +/- 2.87 h, respectively. Of the estruses recorded, 31% had no proestrus and 34% had no metaestrus. More mounting occurred during the day than night (59 vs 41%; P<0.001), and mounting activity had two peaks: 0600 to 0900 h and 1600 to 1900 h. The average number of mounts observed per estrus was 9.2 (ranging from 1 to 58), and the mounts were concentrated at the beginning and end of estrus, irrespective of their duration. Vaginal mucus discharge was detected in 64% of the cows in estrus.