Influence of Age of Dairy Cattle and Season of the Year on the Sex Ratio of Calves and Services Required for Conception

Abstract

The present study was based on records of the dairy herd of the University of Nebraska for the period 1896 to 1934, and covers five breeds, Holsteins, Jerseys, Guernseys, Ayrshires, and milking Shorthorns. In all, 2,090 cows have been included. The purpose was to determine the influence of the age of the bull, the age of the cow, and the season of the year upon the number of services required for conception, and to determine also the influence of these factors upon the sex ratio of calves born, number of twins born, and the percentage of abortion.