Age as a Factor Influencing Breeding Efficiency in a Dairy Herd

Abstract

Seven hundred and six females and forty-three males are included in this study. A of their breeding records shows that when no consideration was given to the age of the bull the number of services required for the first conception was significantly higher than for the following conceptions. Uncalved heifers required a smaller number of services per conception when bred to bulls under four years of age than when bred to older bulls.There was a gradual decrease in the breeding efficiency of bulls as they increased in age, but when used on females of all ages this decreased efficiency, when compared to the yearling age, did not become significant until the bulls reached an average age of six years. Bulls 13 years old and over were significantly less sure as breeders than bulls six years of age.It appears from this study that the use of old bulls is an important factor in the breeding efficiency of dairy heifers, and that dairymen may be justified in mating heifers with young bulls in order that prompt conceptions may result.