Estrus in Relation to Time of Administration of Prostaglandin F2α to Heifers

Abstract

Holstein heifers (95) were given two injections of prostaglandin F2α, the first on day 0 and the second either at 0600 h or 1800 h on day 12. Interval from the second treatment to first observation of estrus did not differ between heifers treated during the morning (69.8 ± 4.4 h) or evening (72.7 ± 5.2 h). However, estrus was detected sooner after treatment of heifers during July 1975 (49 ± 2 h) than after treatment during June 1976 (85 ± 8 h). Estrus began at 64 ± 5, 73 ± 7, and 76 ± 7 h after the second injection during August 1975, October 1976, and December 1975. Heifers treated during the morning in October were detected in estrus sooner (57±3 versus 95 ± 13 h) than those treated during the evening. An interaction of season by time may affect interval from prostaglandin F2α treatment to onset of estrus. © 1978, American Dairy Science Association. All rights reserved.