The effect of progestagen type, PMSG dosage and time of ram introduction on reproductive performance in ewe lambs

Abstract

One hundred and fifty-four March born lowland ewe lambs were allocated to a 2 × 2 × 2 factorial experiment. In October, intravaginal progestagen sponges, containing either 60 mg medroxprogesterone acetate (MAP) or 30 mg fluorogestone acetate (FGA), were inserted for 12 d. Following progestagen withdrawal, each ewe received an intramuscular injection of either 0 or 400 IU pregnant mare serum gonadotrophin (PMSG). Fertile rams were joined 36 or 48 h later, at a ratio of 1:6. The progestagen type employed did not affect conception rate or litter size. PMSG resulted in more active mating activity within the first 4 h of ram introduction (P < 0.01), but there was no difference in lambing rate, and litter size was only slightly increased. When rams were introduced at 36 h, mating took place over a longer period (P < 0.005), pregnancy rate was increased (P < 0.01) and litter size was lowered (P < 0.05).