Cleavage of ova in New Zealand romney ewes

Abstract

Abstract The onset of oestrus was observed in 99 Romney ewes injected with pregnant mares' serum (PMS) on day 12 or 13 of the cycle; in 34 untreated cyclic ewes; and in 26 anoestrous ewes, following treatment with progestagen and PMS. All ewes were mated to entire rams and in vivo recovery of ova attempted 36-101 hours after onset of oestrus. Thirty-eight one-cell ova recovered at laparotomy, and with spermatozoa attached to the zona pellucida, cleaved normally after culture in vivo or in vitro for 24 hours, and were classified as being fertilised when first recovered. Ewes injected with 1,500 i.u. PMS had a significantly lower fertilisation rate of ova than ewes injected with 1,000-1,200 i.u. Failure of fertilisation was noticeable in ewes at the highest ovulation rates. The stages of cleavage of ova relative to the intervals from onset of oestrus were recorded. These intervals were unaffected by treatment of the ewes or by the dose of PMS injected. Within individual ewes having multiple numbers of ovula...