CONTROL OF REPRODUCTION IN ADULT EWES AND EWE LAMBS, AND ESTIMATION OF REPRODUCTIVE WASTAGE IN EWE LAMBS FOLLOWING TREATMENT WITH PROGESTAGEN IMPREGNATED SPONGES AND PMSG

The progestagen impregnated sponge, used in conjunction with a dose of PMSG (Pregnant Mare's Serum Gonadotrophin), was evaluated as a practical method for the control of reproduction in adult ewes and ewe lambs. The method gave good results with adult ewes. The conception rate at the controlled oestrus was 59, 64 and 89% for ewes treated during April, July and October, respectively. Oestrus was effectively synchronized, during the breeding season, in Galway (G), 1 4 Finn 3 4 Galway ( 1 4F), Finn × Galway (FG) and Finnish Landrace (FL) ewe lambs following hormone treatment. The lambing outcome, however, was very variable and depended to a large extent on the breed involved. The percentage of treated G, 1 4 F, FG and FL ewe lambs which actually lambed was 19, 45, 89 and 72, respectively. The causes of reproductive failure in hormone treated Galway ewe lambs were studied. In slaughter experiments, a high ovum fertilization rate (78%) was observed but only 39% of mated animals were pregnant at 26 days post coitum. The results of experiments involving reciprocal transfer of fertilized eggs between ewe lambs and adult ewes suggest that ova produced by Galway ewe lambs have an inherently low potential for continued development. It would appear that it is this, rather than any deleterious conditions in the reproductive tract, which is responsible for low conception rates observed in ewe lambs of this breed. © 1979.