Increasing litter size in three breeds of sheep by superovulation

Abstract

SUMMARYEwes of three breeds, Devon Longwool, Kerry Hill and Welsh Mountain were injected with different levels of Pregnant Mare Serum Gonadotrophin (PMSG) for 3 consecutive years. Within the levels of PMSG examined (0–1500 i.u.) the highest mean litter size was obtained at 1000 i.u. for the Devon Longwool (2·10) and the Welsh Mountain (2·33), and at 1500 i.u. for the Kerry Hill (2·41). This represented a response of 0·66, 1·28 and 0·56 extra lambs born for the Devon Longwool, Welsh Mountain and Kerry Hill breeds, as untreated ewes of these breeds produced 1·44, 1·05 and 1·85 lambs/litter. The lambing percentage attained was, however, lower than the response in litter size indicated, due to the incidence of barren ewes and of lamb mortality.Though the Devon ewes were heavier than the Kerry's, twin lambs out of the latter were bigger than twins from the Devon's. The relationships of body weight and of natural fertility to optimum dosage of PMSG are considered. There is discussion of the maximum litter size and minimum birth weight compatible with the production of viable lambs.