Studies in flock mating of sheep. 5. Incidence, duration and effect on flock fertility of initial sexual inactivity in young rams

Abstract

Seventy-five 1 1/2-year-old Merino rams from four different studs were given three 20-minute libido tests followed by a 48 hour association with oestrous ewes in a flock. Seventeen rams showed no sexual activity during these tests. These inactive (I) rams and some of the active (A) rams were then joined, in pairs (A-A, A-I, or I-I combinations), with 17 flocks of 67 or 125 mature ewes for five weeks. At the end of this period, three rams had still not become sexually active; the remaining 14 began mounting ewes two hours to 34 days after introduction into the flock. Although the effect of ram combination on the number of ewes marked by the rams was not significant, the proportion of marked ewes that lambed was higher (P < 0.05) in the flocks joined with A-A pairs than in those joined with A-I or I-I ram pairs. The proportion of marked ewes that did not lamb to their first marking was lower (P < 0.001) in A-A than in A-I or 1-1 matings. The lower fertility in the flocks joined with A-I or I-I ram pairs could be ascribed to poor mating dexterity and lower libido in the I rams. Observations of ram behaviour were made during the mating period. Competition and aggression between active and inactive rams was only seen after inactive rams became sexually active.