Environmental and genetic sources of variation for seminal quality in mature Holstein bulls

Various environmental and genetic factors that influence seminal quality were evaluated for 149 Holstein bulls used extensively in nine artificial insemination organizations (studs). These bulls were sons of 16 sires. Seminal quality was measured by percent progressive motility immediately postthaw and after incubation at 3 h, 37 degrees C, percent intact acrosomal membrane after incubation at 3 h 37 degrees C, and percent primary and secondary abnormalities. Semen was thawed at 37 and 24 degrees C. Spermatozoal concentration was counted with a hemocytometer. Bull age and season of collection were determined. Interaction of stud X thaw existed for both motility assessments and intact acrosomes, but 37 degrees C thaw resulted in higher motility and acrosomal integrity across all studs. Motility at zero hour was affected by season. Secondary abnormalities were influenced by season and stud X season. Interaction of thaw X season existed for incubated motility, which also was influenced by concentration and age. Age influenced secondary abnormalities. Heritabilities and repeatabilities (%) were .21, 44; .40, 34; .81, 74; and .31, 50 for 0-h motility, intact acrosomes, primary abnormalities, and secondary abnormalities. Genetic correlations were 0-h motility with acrosomal integrity and primary and secondary abnormalities, .88, -.70, -.93; acrosomal integrity with primary and secondary abnormalities, -.90, -.05; primary with secondary abnormalities, -.12. Selection for semen quality could improve fertility of bulls.