Estrus, Estrous Cycles, Ovulation Time, Time of Service, and Fertility of Dairy Cattle in Louisiana

The mean duration of estrus for 1,460 estrous periods for 270 cows and heifers was 11.9 hr., with heifers having significantly longer estrous periods than parous cows. Nonstanding estrus was observed in 10.1% of the estrous periods. Est,"as after conception was exhibited by 14.4% of the animals and involved 3.4% of the estrous periods. Ovulation occurred 12.4 hr. after the end of estrus. Optimum time for insemination was 7-12 hr. after the onset of estrus. Anestrus occurred one or more times in 33.4% of the animals, representing 10.6% of the expected estrous periods. It was calculated that anestrus would have increased 19.9% with only 0600 and 1800 hr. obseiwations; whereas, an additional check at 1,200 hr. increased the incidence only 10.0% above that which occurred during 6-hr. observational periods. Monthly PBI levels were inversely related to environmental temperature and humidity.