Heterosis Estimates for Measures of Reproductive Traits in Crossbred Boars

Abstract

Data on 354 Duroc, Yorkshire and reciprocal cross boars were utilized for the estimation of heterosis for measures of reproductive traits in boars. Testis length and width of intact boars were measured at 56, 84, 112, 140 and 168 days of age. At 168 days, testes were excised and evaluated for paired testes width, right testis length and weight, sperm per gram of testis, total sperm in testes and weight and sperm counts of epididymides. Crossbred boars had heavier body weights (P<.05) and tended to have longer, wider testes at all ages. Excised testes of crossbred boars were larger (P<.01) and had higher (P<.05) numbers of sperm. Crossbred boars also had more sperm per gram of testis (P<.05), which may be considered a measure of efficiency of sperm production. Heterosis values for length, weight, total sperm, sperm per gram of right testis and combined width of testes were 8.5, 25.4, 33.7, 23.3 and 10.4%, respectively. Adjustment for body weight tended to decrease heterosis estimates, to 2.5, 8.1, 14.4, 15.1 and 4.5%, respectively. These results suggest that the larger testes and higher testes sperm counts of crossbred boars were due in part to an increase in activity of spermatogenic elements that are not associated with an increase in body weight. Heterosis values for epididymal sperm in the caput region were large, whereas heterosis values for sperm in the cauda region were small. This may suggest that crossbred boars were eliminating more sperm either through increased frequency of masturbation or increased sperm output per masturbation.