Postpartum ovarian function of dairy cows in a tropical environment.

Intervals from parturition to first estrus and to the first three ovulations were studied in 25 Holstein and 31 Jamaica Hope cows in Jamaica. Casual observations for signs of estrus were supplemented by twice nightly observation periods. Samples of blood plasma were obtained twice weekly from all cows and assayed for progesterone. The progesterone profile for each cow was used to determine when ovulations occurred. Intervals and standard deviations from parturition to first, second, and third ovulations were 19.8 +/- 8.8, 39.4 +/- 9.0, and 58.6 +/- 9.2 days for Holsteins, which were shorter than the same intervals for Jamaica Hope cows (28.7 +/- 15.6, 46.9 +/- 13.6, and 66.3 +/- 12.6 days). Intervals from parturition to first detected estrus were 46.0 +/- 21.4 days for Holsteins and 45.5 +/- 18.7 days for Jamaica Hopes. There were no significant differences between seasons of calving in intervals to ovulations or in intervals to first detected estrus. Percentages of cows detected in estrus at the first, second, and third ovulations were 19, 61.9, and 57.8% for Holsteins and 43.3, 55.2, and 73.1% for Jamaica Hopes. Holstein cows kept in a tropical environment are capable of returning to a cycling, rebreedable state and of showing detectable signs of estrus as soon after calving as can be expected reasonably.