Oestrus, ovulation and ovum transport in young Merino ewes

Three groups of Merino ewes were studied to determine the effect of age of ewe (1 1/2 vs 2 1/2 years) and parity (0 vs 1) on the oestrus-ovulation relation and on the rate of ovum transport through the oviduct. Parity rather than age increased duration of oestrus from 11.6 hours in nulliparous I 1/2-year-olds to 17.4 hours in primiparous 2 1/2-year-old ewes (P < 0.01). As a result, 65% of primiparous ewes were still in oestrus by 15 hours before ovulation (the optimum time for conception) compared with 28.5% of the nulliparous ewes (P < 0.05). Ovum transport through the oviduct in the 48 hours after ovulation was similar in all groups. The study provides supportive evidence for the hypothesis that nulliparous 1 1/2-year-old ewes have higher ovum wastage than older, parous ewes because of their shorter duration of oestrus.