Follicular dynamics, ovulation time and pregnancy rate in bos taurus/bos indicus cows induced to cyclicity with norgestomet in the mexican humid tropic

Abstract

To assess reproductive behaviour in postpartum anoestrous, 48 Bos taurus/Bos indicus cows were randomly allocated in a 2x2x2 factorial design. Factors being: dry and wet season of the year, induced (IO) or subsequent spontaneous oestrus (SO) and feed unsupplemented or supplemented (FS). Oestrus was induced by implanting norgestomet. Oestrus induction and ovulation rates were higher in the dry season and in the IO group (P<0.05). Time of oestrus display after implant removal was shorter in the dry season and in cows without FS (P<0.05). Average time of ovulation after oestrus detection was 25±1.7 h (P>0.05). Pregnancy rate was higher in the dry season (P<0.05). Follicular dynamics was not affected by season of the year, FS and oestrus type (P>0.05). In conclusion, the use of norgestomet for induction of cyclicity improved fertility in the dry but not in the wet season. © GSP, India.