Abstract

Progesterone (P4), oestradiol benzoate (ODB) and prostaglandin F2a (PGF) have been used separately and in combination to synchronise oestrus in cattle by reducing the luteal phase of the cycle or delaying pro-oestrus after luteolysis. This latter mechanism can result in precise synchrony but with reduced fertility. In the process of attempting to improve synchrony and fertility, a series of four trials was completed with dairy heifers. Each trial was based on the use of a CIDR-B device for 7 to 10 days with or without 10 mg ODB in a gelatin capsule and with an injection of PGF from 2 to 4 days before device removal or at device removal. The results of these trials showed that injecting PGF before device removal could improve synchrony (in terms of animals inseminated at 48 h after device removal) but reduced pregnancy rates to first insemination by 5% to 10%. Incorporating ODB delayed the post-treatment interval to oestrus and insemination with a 7-day CIDR regime but improved synchrony with a 9 or 10 day CIDR regime. If the use of ODB was combined with an injection of PGF 4 days before CIDR device removal as part of a 10-day CIDR programme, the 48 h post-treatment synchrony rate was 93% and the pregnancy rate was 56%. Excluding the ODB from this programme reduced the 48 h synchrony rate to 87% and the pregnancy rate to 45%. These results are additional evidence that combing ODB with P4 is altering ovarian follicle wave patterns with consequent effects on synchrony patterns and fertility.

WH, McMillan

Proceedings of the New Zealand Society of Animal Production, Volume 53, , 259-262, 1993