Abstract:
Sexual activity, serving capacity, mean number of mounts per serve and mean testis diameter were measured in 286 Border Leicester, BLI (a 'high fertility' sheep related to the Border Leicester) and BLI x Border Leicester rams at 1.5, 2.5 or 3.5 years of age. Rams were allowed two 20-minute introductory periods with spayed oestrous ewes, and then were given two 1-h pen mating tests during which their serving capacity (the mean number of serves in the two tests) and mounts per serve were counted. Rams which commenced mounting in introductory or 1-h tests were classed as sexually active. Among 1-5 and 2.5-year-old rams, 68.9 and 65.4%, respectively, were sexually active, while all 3.5-year-old rams were active. Mean testis diameters for inactive rams were smaller (P<0.05) than for active rams in both 1.5- and 2.5-year-old rams. There were breed type differences in activity, serving capacity and mean testis diameter at 1.5 years of age, but not at other ages. BLIs were less active at 1.5 years than other types, but BLIs and Border Leicesters did not differ in either their serving capacity or testis diameter. BLI x Border Leicesters generally had greater (P<0.05) serving capacities and testis diameters than other types, suggesting possible advantages for these rams at early joinings. Sire effects for serving capacity were not significant, but were significant (P<0.05) for mounts per serve, and for testis diameter at 1.5 years old. Activity status was highly repeatable (0.83) between 1.5 and 2.5 years and testis diameter was moderately repeatable (0.41). Repeatabilities for serving capacity and mounts per serve, in active rams, were not significant. Correlations between serving capacity and testis diameter were not significant for active rams, while serving capacity and mounts per serve were generally negatively related. Mean testis diameter was significantly (P<0.05) correlated with liveweight at 1.5 years but not at other ages. Liveweight at 2.5 years was positively (P<0.05) related to mounts per serve and negatively (P<0.05) related to serving capacity.