[Correlation between the number of inseminated spermatozoa and results of fertilization in dairy cattle].

Of forty-seven Friesian bulls 216 ejaculates were split-samples and diluted to concentrations varying from 3.75 to 40 million spermatozoa per insemination dose. The semen was frozen in 0.25 ml French straws. After freezing, the number of spermatozoa per straw was checked with an electronic particle counter. Optimum fertility rates were achieved with a concentration of 15 million spermatozoa per insemination dose. Higher numbers of spermatozoa per insemination did not result in a further increase in conception rates. The optimum dosage of spermatozoa was dependent on the fertility level of the bull. In bulls with high, average or low fertility, the maximum fertility levels attainable were achieved with 7.5, 10 or 15 million of spermatozoa per insemination dose respectively. An interaction between season and insemination dose could not be shown to be present.