Variations in Bull Semen and their Relation to Fertility

Summary 1. A study of the semen of ten bulls used in the University of Missouri dairy herd has been made and the semen properties compared with the bulls’ breeding records. 2. The property of the semen most nearly correlated with fertility was the time of survival with vigorous motility hi semen stored at 40° Fahrenheit. 3. Among the different bulls, other properties of the semen such as pH, concentration, volume, percentage of abnormal spermatozoa, and initial motility were not correlated with the bull's fertility or time of survival with good motility except in the case of one bull of poor fertility which produced semen very high in abnormalities and very low in initial motility. 4. Among separate ejaculates from the same bull initial motility was roughly correlated with viability in storage. 5. Wide variations in all properties of the semen were observed, among ejaculates of different bulls as well as among ejaculates of the same bull. 6. It is proposed that a bull's fertility should be rated from examinations of at least five semen samples collected over a period of at least two weeks, and that the suitability for use or storage of a sample of semen from a fertile bull can best be determined at time of collection by examination for motility.