Ovum production: action of various gonadotrophins in sheep and goats

Abstract

Following progesterone pre-treatment a total of 45 anoestrous ewes consisting of equal numbers of Merino, Angora, and Boergoat ewes was treated with gonadotrophin according to three different schedules. Detailed observations were made on behavioural response and, at laparotomy, on ovarian morphology and ovum recovery. Merino ewes showed the highest overall ovulation rate (7·1) followed by Boergoat (4·8) and Angora ewes (3·0). Pregnant mare serum (PMS) was highly variable in sheep and resulted in poor responses in goats. A horse anterior pituitary gonadotrophin (HAP) resulted in variable but marked follicular growth in all breeds; however, in goats the majority of follicles failed to ovulate. PMS combined with simultaneous human chorionic gonadotrophin (PMS/HCG) suppressed ovulation to some extent in sheep but markedly potentiated follicular growth and ovulation in goats and was the most predictable of the three gonadotrophins. A small but significant difference of total follicular growth in favour of the right ovary was found. Large persistent follicles were encountered in most animals and increased proportionally with the number of ovulations. These follicles persisted up to 70 hours after oestrous onset, where after regression was rapid. Excessive follicles were accompanied by an increased incidence of unfertilized ova. Recovery of cleaved ova was also seriously hampered by accelerated tubal transport in Merino ewes, but no such phenomenon was encountered in goat ewes, which in fact exhibited evidence of retarded tubal transport of ova in relation to oestrous onset. Oestrus commenced in 84 per cent of all animals on the second or third day following gonadotrophin treatment and was longer than usual with PMS and considerably shortened by PMS/ HCG. Excessive persistent follicles hastened the onset of oestrus but the numbers of follicles and ovulations had no effect on oestrous duration. Indirect evidence that the endogenous luteinizing hormone contribution is optimal in sheep, marginal in Boergoats and deficient in Angora goats is discussed and a relationship to the high incidence of gestational failure in Angora ewes suggested.