Relationship between Level of Milk Production and Breeding Efficiency in Dairy Cattle

MANY dairymen are of the opinion that they experience more breeding difficulties in their high producing cows than in close relatives which produce at lower levels. Clapp (1937) observed that cows milked twice daily came into heat after calving 23 days earlier on an average than did cows milked four times daily. However, it was not ascertained whether the level of production or the frequency of milking was responsible for this difference. New Zealand workers (Anonymous, 1940–1941), in a progress report, stated that no definite conclusions can be drawn relative to the association of poor fertility with high production. However, they reported that there appeared to be a strong suggestion of better fertility in the lower producing herds; also, that the incidence of sterility and abortion showed a definite association with the higher producing herds. Lewis and Horwood (1950) found from a study on the Michigan State College Holstein Herd that production during the previous lactation was not related to the breeding results encountered during the following lactation.