Performance and progeny testing of artificially and naturally reared ram lambs
Performance and progeny tests were carried out between 1975-1977 to obtain estimates of genetic variation in the growth rate of artificially reared Suffolk ram lambs both between and within flocks. It was found that there was individual variation in rams' breeding value and moderate heritability estimates of growth rate were obtained. Two further experiments were designed to investigate a problem arising from the performance test of 1975, when 24% of the sires failed to mate with ewes when they were introduced to them for the first time. The objectives of the first experiment were to investigate the effects of method of rearing and female company on the attainment of puberty. The second experiment was designed with the additional objectives of investigating whether early weaning of naturally reared ram lambs could provide an alternative to artificial rearing from birth. The effects of repeated pen libido and semen tests on sexual performance and semen traits were also investigated. The results obtained indicated that lambs which were either artificially reared, or naturally reared, but early-weaned at two months of age, attained puberty at an earlier age than those reared naturally with their dams to six months of age. It was also found that repeated libido testing significantly improved sexual performance in terms of number of mounts and number of ejaculations achieved within the 20-minute test period.