Estimates of heterosis for sexual activity in boars

Data on 118 Duroc, Yorkshire and reciprocal cross boars were utilized to evaluate the effect of crossbreeding on mating behavior. Boars were penned with an estrous gilt on 2 consecutive days. Number of mounts (proper and improper), sexual interest score and whether a successful mating occurred were recorded. Times at which each of these events occurred were recorded also, allowing calculation of times to first mount, to final mount and to completion of mating. Most importantly, more crossbred boars completed a mating than purebred boars (69 vs 27%). Crossbreds had greater sexual interest (P less than .05), more mounts and a higher proportion of properly oriented mounts (P less than .05). Crossbreds also began mounting activity (first mount, first proper mount and final mount; P less than .05) earlier and required less time to complete a mating (P less than .05) than purebred boars. Heterosis values for number of proper and improper mounts, proportion of proper mounts and sexual interest were 2, 53, 32 and 52%, respectively. Time to first mount, to final mount and to completing mating had heterosis values of -34, -29 and -20%, respectively. Scrotal measures taken at 140 and 168 d and at post-trial castration, as well as excised testes measures and sperm numbers, showed heterosis; however, no consistent associations between these traits and behavior traits were found. These data suggest that crossbred boars were more sexually active than purebred boars, perhaps due to an advanced physiological or behavioral stage.