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

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Abstract
Four controlled expts. were conducted to study dilution levels from 1:100 to 1:300. A total of 11,372 services from 69 collections from bulls selected for high fertility were involved. The semen was diluted in yolk-citrate or yolk- citrate -sulfanilamide. In every expt. there was a downward trend with increase in dilution level, but none of the differences was significant. The relationship between non-return percentages and spermatozoon numbers at dilutions above 1:100 appears to be curvilinear. As the number of spermatozoa decreased from approx. 12 million to 6 million per ml. of diluted semen, there was a decrease of approx. 0.5 in 60- to 90-day non-return percentage per million decrease in number of spermatozoa. Within this range in spermatozoon numbers, which corresponds roughly to dilution levels of 1:100 and 1:200, respectively, there is, therefore, an over-all decline in non-return rate of approx. 3%. When the diluted semen contained less than 6 million spermatozoa per ml., there was a drop of over 2.6% in non-return rate per million decrease in number of spermatozoa per ml. Livability of spermatozoa decreased markedly with increase in dilution rate. Correlation analyses indicate that decrease in spermatozoon numbers was more important in causing the decrease in non-return rates than the direct depression of motility by high dilutions.