Nonreturn Rate of Artificially Inseminated Dairy Cows as Affected by Age of Semen, Breed of Bull, and Season

Abstract
The percentage of nonreturns declined in an essentially linear manner. The rate of decline varied from 5 to 11 percentage points for each additional day of age of the semen, depending on breed. Breeds ranked in the following order of decreasing efficiency: Holstein, Brown Swiss, Jersey, Ayrshire, Guernsey, Milking Shorthorn. The decline in nonreturn rate with the age of the semen was least in the winter, and essentially the same during the other 3 seasons.