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An Analysis of the Components of Variance in Calving Intervals in a Range Herd of Beef Cattle¹

New Mexico Agricultural Experiment Station^,3

Abstract

A CALVING interval is defined as the time elapsing from the date of birth of a cow's calf till the birthdate of her next calf. The calving interval comprises the interval from calving to first heat, number and length of estrus cycles, and length of gestation. Any practices designed to shorten the length and increase the constancy of the calving interval would be desirable.

Materials and Methods

The data used in this study were taken from the records on the Angus cattle at the El Sueco Ranch in Chihuahua, Mexico.

Under the system of breeding used at this ranch, a cow in heat was brought into a central bull barn, where she was bred by natural service to a selected bull. The recently-bred cow was then put into a pasture and observed for return to heat. If the cow returned to heat, she was bred again to a selected bull. After the non-return to heat indicated that the cows had settled, they were turned into a calving pasture with one bull.

¹ Published with the approval of the Director of the New Mexico Agricultural Experiment Station as Paper No. 80 in the Journal Series.

² The authors are indebted to Captain Ian Benton, Chihuahua, Mexico, for the use of his data and to Dr. Morris Finkner, biometrician with the New Mexico Agricultural Experiment Station for his assistance in the statistical analysis.

³ Department of Animal Husbandry in cooperation with the Bureau of Animal Industry, USDA, and the state experiment stations under Western Regional Project W-1 on Beef Cattle Breeding Research.