The lengths of estrus, and intervals from the beginning of estrus to ovulation and from the end of estrus to ovulation after induced or spontaneous luteolysis, and after prostaglandin application were evaluated in 35 Gir and 12 Guzera cows during the winter and summer seasons of two consecutive years. No difference in length of estrus between Gir (12.13±0.47h) and Guzera (12.30±0.63h) was observed (P>0.05). The length of estrus was not influenced (P>0.05) by induced or spontaneous luteolysis and season. No differences (P>0.05) in lengths from the beginning of estrus to ovulation and from the end of estrus to ovulation between Gir (29.30± 0.96h and 17.28± 0.93h, respectively) and Guzera (28.33± 1.26h and 16.04± 1.21h, respectively) cows, between induced and natural estrus, and between seasons were found. The prostaglandin application to beginning of estrus interval was shorter (P<0.05) in Gir breed (64.68± 2.41h) than in Guzera breed (73.47± 3.45h). The prostaglandin to ovulation interval was similar (P>0.05) between Gir and Guzera (96.62± 4.25h and 104.01± 6.51h, respectively). Large variation in the length from prostaglandin application to beginning of estrus, and high correlation between this interval and ovulation time were observed. These results suggest that the synchronization of estrus and ovulation was not sufficiently precise to adopt fixed-time AI.
bovine; estrus synchronization; ovulation; zebu
