Abstract :
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.
