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Fertility and Livability of Bull Semen Diluted at Various Levels to 1:300

American Foundation for the Study of Genetics, Madison, Wisconsin

ABSTRACT

1. Four controlled experiments were conducted to study dilution levels above 1:100. A total of 11,372 services from 69 collections from bulls selected for high fertility were involved. In every experiment there was a downward trend with increase in dilution level, but none of the differences was significant.
   
2. In two of these experiments with a total of 7,787 services from 54 collections, accurate spermatozoan counts were made and regression coefficients were calculated. The citrate-sulfanilamide-yolk diluter was used. The relationship between non-return percentages and spermatozoan numbers at dilutions above 1:100 appears to be curvilinear.
   
3. As the number of spermatozoa decreased from approximately 12 million to 6 million, there was a decrease of approximately 0.5 in non-return percentage per million decrease in number of spermatozoa per insemination. Within this range in spermatozoan numbers, which corresponds roughly to dilution levels of 1:100 and 1:200, respectively, when 1 ml. of semen is used per insemination, there is, therefore, an over-all decline in non-returns of approximately 3 per cent.
   
4. When the diluted semen contained less than 6 million spermatozoa per ml., there was a drop of over 2.6 per cent in non-returns per million decrease in number of spermatozoa per insemination.
   
5. Motility observations are reported on a total of 128 samples from 32 collections studied at 2-day intervals during a storage period of 12 days. Dilution levels of one to 50, 100, 200 and 300 were compared. There was a marked decrease in livability of spermatozoa with increase in dilution rate.
   
6. Correlation analyses indicate that decrease in spermatozoan numbers was more important in causing the decrease in non-return rates with the dilution levels studied in this experiment than the direct depression of motility by high dilutions.