Descriptive characteristics of estrus in dairy cows during winter and summer in Puerto Rico

Abstract

The study was undertaken to determine the duration of estrus and standing heat during winter and summer, to evaluate the effect of environmental temperatures on estrus and to determine the response interval to synchronization with prostaglandin F20 (PC; Lutalyse). Groups of eight cows each were synchronized at weekly intervals using two intramuscular injections of 25 mg of PC at 11 -day intervals, regardless of their estrous cycle phase. Twenty-four hours following the second PC injection, the cows were continuously observed for a 120-hour period recording all reasonable estrus signs. Cows were artificially inseminated 12 hours after the onset of estrus. Independent variables like season and maximum and minimum temperatures had no significant effects on the reproductive variables studied. The mean length of the interval between the second PC injection and the onset of estrus was 51.2 and 57.0 h for winter and summer, respectively. Considerably more cows were observed in estrus 48 h after me second PC injection, both in winter and summer. Mean estrus length was 20.4 and 16.0 h and mean duration of standing heat was 12.1 and 10.5 h in winter and summer, respectively. Onset of estrus ocurred more frequently during diurnal hours with no indication of interference from the farm’s routine activities. The overall occurrence of silent estrus was 32% (37% and 27% in winter and summer trials, respectively). Although the duration and intensity of estrus did not differ significantly between seasons, pregnancy rate was significantly higher in winter than in summer trials (62 vs. 26%, respective[y) indicating that fertilization and/or embryonic mortality were markedly affected during warmer months. Principal component analysis showed a definite pattern of estrous behavior in winter and a lack of such order in the summer indicating a probable influence of climatic elements.