The main factor limiting fecundity in sheep is the low ovulation rate (Hanarahan, 1980). The relationships between body condition, level of nutrition and ovulation rate, and the ability to increase fecundity by flushing ewes prior to mating, are all well established (Gunn, 1983). In upland ewe flocks, flushing is generally attempted by the use of saved autumn pastures. However, the seasonal variation in grass growth often results in the degree of flushing desired not always being possible and leaving the flockmaster seeking a viable option.
The present investigation examined two possible alternative strategies for increasing the fecundity of upland ewes. Improving body condition prior to mating by supplementary feeding was compared with the recently developed technique of increasing ovulation rate by active immunisation against androstenedione (Scaramuzzi, Cox and Hoskinson, 1982).