Genetic variation in testicular development and its relationship to female reproductive traits in swine

In situ length and width of both testes and body weight were recorded on 40 Chester White, 60 Landrace, 60 Large White and 62 Yorkshire boars born in the spring and on 57 Duroc, 54 Hampshire, 57 Pietrain and 50 Spot boars born in the fall. Testicular biopsies on one-half of the boars in each breed group were evaluated for percentage of tubules with complete spermatogenesis and for diameter of tubules. Testicular volume of both testes was estimated at 98 and 154 d of age and 36 and 81 kg. Breed effects were significant for all testicular traits except testicular volume at 36 kg in the spring farrowing and testicular volume at 98 d of age in the fall farrowing. The estimate of heritability for testicular volume was low at 98 d of age (.12 +/- .14) but large at 154 d of age (.55 +/- .12). Heritability estimates for testicular volume were lower at constant weights (.11 +/- .14 and .14 +/- .12) than at constant ages (.12 and .55). Heritability estimates for traits measured by biopsy were moderate to large (.22 +/- .22 to .78 +/- .18). Phenotypic correlations of in situ testicular volume with traits measured by biopsy were moderate and positive when estimated within a breed (.16 to .52). Genetic correlations of testicular volume at constant ages and weights with traits measured by biopsy were moderate to large and positive (.58 to greater than 1.0); similar correlations among bred means were quite variable (-.35 to .91). Selection for increased testicular volume would not be antagonistic to selection goals for growth and backfat. However, selection for improvement in traits measured by biopsy may result in undesirable changes in growth rate and backfat probe. Genetic correlations of testicular traits with age at puberty and litter size of females were not consistent in magnitude or sign between the two estimation procedures.