Relationship between the testis size in male pigs and reproductive traits in their progeny

Selection for female farrowing performance is challenging to the swine industry due to the low heritability. Previous studies have suggested testis size as an indicator of reproductive performance. Thus, to determine the effectiveness of measuring testis size to identify sires of reproductive superior sows, 161 Yorkshire and Landrace boars were measured for width (TW) and area (TA). Farrowing performance was collected for 384 sows, daughters of 13 of the 161 boars. For heritability estimates (h(2)), the fixed effects of age (boar traits only), breed, contemporary group (CG), and parity (sow traits only), and the random effects of animal and permanent environment (sow traits only) were included in the model. Poisson phenotypic regression of the reproductive traits of daughters on the testis size of sires was performed including the fixed effects of parity, breeds of sow and sire, and TW or TA, and the random effects of sow and CG. For testis size, h(2) were 0.69 and 0.66 for TA and TW, respectively. For reproductive traits, h(2) ranged from 0.01 to 0.18. There were quadratic and linear relationships (P < 0.05) between reproductive traits in sows with TA and TW, respectively. Optimal performance for survival traits was obtained when TA of sires was within 17.2-18.5 cm(2), which did not overlap with the range that resulted in greater mortality (15.8-16.3 cm(2)). With regards to TW, there was a linear increase of survival traits (P < 0.05) as TW increased, but not mortality (P >= 0.11). Phenotypic assessment of testis size of sires may be a useful tool to cull animals for breeding, improving female performance.