USE OF VAGINAL SPONGES IN SPRING BREEDING OF MUTTON MERINO AND CROSS-BRED EWES

Fifty-nine Mutton Merino and cross-bred 2-year-old and older ewes were allotted to two groups according to age, weight and breeding performance in the preceding 1966/67 in-season. In the experimental ewes the treatment started on 22 March 1967 and consisted of vaginal sponges (Syncro-Mate) inserted for 17 days and 750 i.u./ewe of P.M.S. injected on the day of the removal of the sponges. As from 1 March, all the ewes were ‘teased’ daily but hand service commenced on 20 April, to coincide with the 13th day after the removal of the sponges. At the time of sponge insertion, approximately a third of the ewes, in each group, were already cycling. The treatment advanced the average post-treatment oestrus by 8 days, out of a possible 15 days, synchronized it in 70% of ewes and shortened the tupping season in 97% of treated ewes to 9 days (23 days in controls), but otherwise the performance of the treated ewes (and their offspring) did not differ from that of the controls. In both groups forty ewes lambed (68%) and fifty lambs were born (85%). Out of nineteen dry ewes, five were in anoestrus and in at least nine, an early death of the embryo could be suspected. Among the reproductive activities during the preceding in-season, date of weaning, days of suckling and barrenness may be implicated in the failure to breed in the spring. © 1969, Cambridge University Press. All rights reserved.