Reproductive performance of rams in three producer range flocks: Evidence of poor sexual behavior in the field

Poor mating behavior increases ram costs and extends the lambing season while decreasing genetic progress. Producers recognize the importance of ram libido; however, time, labor, and facility constraints limit routine evaluation of males for libido. The current experiment determined the incidence of low- and high-sexually performing rams based on the number of lambs sired by each ram in three range flocks. Rams were evaluated for breeding soundness prior to joining with females. Genomic DNA was extracted from blood samples collected from all rams, and approximately one-third of the lambs and their dams. Microsatellite markers were used to determine parentage. Number of lambs expected to be sired by each ram was established by calculating 99% confidence intervals, based on the expectation that each ram would have equal number of lambs. Rams siring more or less lambs than expected were categorized as high or low sexually performing rams, respectively. Paternity was established for >80% of the lambs sampled. Rams which had higher than expected numbers of lambs made up 23-29% of the ram population but sired from 39.4% to 70% of the lamb crop. Low performing rams (23-43% of the ram population) sired from 3.2% to 16.2% of the lamb crop. Since fertility was evaluated prior to mating, differences in ram fecundity may reflect the expression of sexual behavior in a multi-sire range flock setting. Rams are generally selected for breed characteristics and potential influence on flock genetics will be greater for high- than low-sexually performing rams.