OESTRUS SYNCHRONIZATION, ARTIFICIAL INSEMINATION AND EARLY REBREEDING IN YANKASA SHEEP

COMPONENTS of an intensive sheep production system including oestrus synchronization, artificial insemination and early rebreeding were investigated in two trials with Yankasa sheep. Treatment of ewes with progrestagen pessaries for 12 days resulted in good synchronization of first and second post-treatment oestrus. In Trial I, (January–February, 1982) 33 ewes were treated, of which 81.8% showed oestrus within 4 days after the end of progrestagen treatment while 72.7% showed a second oestrus within 21 days. In Trial II, (August – September, 1982), 48 eyes were treated, of which 87.5 and 77.1% showed first and second oestrus respectively over the same periods as in Trial I. Mean interval (± s.e.m) between first and second induced oestrus in both trials was 16.4 ±0.1 days (n = 61). About 90% of ewes exhibiting oestrus were detected 2 to 4 and 17 to 20 days after progrestagen treatment for first and second oestrus respectively.  Lambing reates of ewes to artificial insemination or natural mating at the second induced oestrus in Trial I were 50.0 and 91.7% respectively, Corresponding lambing rates in Trial II were 65.0 and 86.70%.  Rebreeding interval in ewes which lambed in Trial I was 59.1 ±0.8 days following commencement of progestagen treatment approximately one month after lambing. Lambing rate in this group was 78.6%.