Conception Rate in Dairy Cattle by Artificial Insemination at Various Stages of Estrus

A breeding experiment with 295 dairy cows and heifers of the Jersey, Guernsey, Ayrshire, and Holstein breeds was conducted in the University of Nebraska dairy herd. The females were given artificial services at various stages of estrus to determine the effect of time of service upon conception. The results obtained indicate the potential benefits in higher percentage of conception in females bred during the middle of estrus, toward the end of estrus, and those bred in full heat and rebred in 24 hours. The latter is usually not very practical, especially in artificial breeding rings, but there are occasions when it may be desirable to follow this procedure. The results also show that a good rate of conception is obtained in females bred as late as six hours after the end of estrus. The low rates of conception in experimental groups bred long after the end of estrus indicate that it is seldom practical to breed females later than six hours after estrus ends. Statistical treatment of the data verified these conclusions