The Importance of Numbers of Spermatozoa in Relation to Semen Quality and Fertility of Dairy Bulls

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Abstract
Studies of the semen quality and fertility of 10 dairy bulls routinely used in artificial breeding in 1949 and 1950-51 revealed that nos. of spermatozoa in ejaculated and diluted semen are very important. Correlation and regression coefficients between numbers of spermatozoa and fertility were calculated on 275 ejaculates with 8356 1st services in 1949 and on 297 ejaculates with 13,156 services in 1950-51. The correlation coefficients between nos. of motile spermatozoa per ml. of diluted semen and fertility in 1949 were 0.219, 0.526 and 0.110 on a total, among bulls and within bull bases, respectively. The coefficient on the total basis was the only significant one (P <0.01). In a semen dilution expt. involving 2591 1st services, fertility levels (% 60- to 90- day nonreturns to first services) were 63.6, 64.5 and 58.2% for dilution levels of 12, 6 and 2 million motile spermatozoa per ml. or per insemination. It was concluded that semen samples with a spermatozoan concn. as low as 500 million per ml. will give as good fertility results as more concentrated ones, provided the semen is diluted on the basis of numbers of motile spermatozoa, 6 million or more per ml. Also, more uniform fertility results among and within bulls can be obtained when the semen is diluted on the basis of a constant no. of motile spermatozoa.