Induction of Ovulation in Anoestrous Ewes Using Gonadotrophins

Abstract

Seasonal anoestrus is associated with a reduction in the frequency of pulsatile release of LH in all breeds of sheep examined so far. We have investigated the gonadotrophic requirements for ovulation and formation of a corpus luteum in 4 breeds of sheep with differing lengths of anoestrus by infusing LH in a pulsatile manner to reproduce the pattern observed during the follicular phase of the oestrous cycle with or without addition of FSH (a) In Finn-Merino ewes with “shallow” anoestrus, pulsatile LH administration alone induces ovulation and normal luteal function. (b) In Scottish Blackface ewes with a long “deep” anoestrus, neither pulsatile LH nor FSH induced ovulation. (c) In Welsh and Damline ewes with a moderate degree of anoestrus, pulsatile LH induced ovulation but with a high incidence of inadequate corporus luteum (C.L.) function. Addition of FSH in the dose and duration used did not significantly increase the incidence of normal C.L. It is concluded that the gonadotrophic requirement for follicular development, ovulation and formation of a normal C.L. during seasonal anoestrus vary depending on the genetic background of the sheep.