Effects of Dilution on Motility of Bull Spermatozoa and the Relation between Motility in High Dilution and Fertility

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Abstract
The effect of high dilution upon motility of bull spermatozoa was studied on 6 semen samples from each of 5 bulls. The semen was diluted 1:10 and also successively in 8 different dilutions from 1:100 to 1:12800. Two different diluents were used, 0.9 percent sodium chloride and 0.08 M sodium citrate. The percentage of motile sperm decreased markedly in the higher dilutions with either diluent.The average motility over all dilutions was greater in the chloride than in the citrate solution but the resistance to dilution as indicated by the maximum dilution which would support motility was greater in the citrate solution. Significant differences between the samples of semen from different bulls were observed and also between the different samples from the same bull. Reconcentration by centrifugation of highly diluted sperm failed to restore motility. The inhibition of motility was just as great when semen was diluted in vacuum as when diluted in air. Egg yolk when added to the citrate solution gave a marked increase in the resistance of the sperm to dilution. Possible correlations were sought between different indices of motility of the spermatozoa and the fertility of the same samples when used in artificial insemination. No significant correlations were found when studied between samples within bulls. There was, however, very slight evidence between bulls for a correlation between motility in a dilution of 1:10 and fertility and also between the highest dilution in which motility was shown and fertility, dilution in both cases being in sodium citrate solution.
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