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Size of Calves at Weaning as a Permanent Characteristic of Range Hereford Cows¹

Iowa Agricultural Experiment Station

Abstract

The extent to which the weaning weight of her calf is a permanent characteristic of a range Hereford cow was studied, using the weaning weights of all the 745 calves from the 180 Line 1 cows which had calved at the Miles City Station at least twice during the period 1938–1948.

The records were adjusted for the following factors thought to influence the weaning weight of calves: Year in which the record was made, age of dam, sex of calf, age at weaning, inbreeding of dam, and inbreeding of calf.

The average uncorrected weight of all calves was 393 lbs. The standard deviation of adjusted weights was 27 pounds. The average age at weaning was 176 days. The average inbreeding of all calves was 12.4%. The average inbreeding of all dams was 5.9%.

Differences between cows accounted for 52 percent of the variance in the calves corrected weaning weights. Therefore, the extent to which the weaning weight of calves is a permanent characteristic of range Hereford cows, as determined from this study, is 0.52. The repeatability of 0.52 is based on differences between cows which made their records during a 10-year interval and may, therefore, be slightly high for comparing cows born in the same year.

This repeatability is high enough to permit reasonably accurate selection of cows for high life-time production on the basis of the first calf weaned.

¹ Journal paper No. J-1882 of the Iowa Agricultural Experiment Station, Ames, Iowa. Project No. 1055.

² Now with the Department of Animal Husbandry, University of Nebraska. The author is indebted to Dr. L. N. Hazel, Professor O. Kempthorne, and Dr. J. L. Lush for their guidance and assistance. Further acknowledgement is made to J. R. Quesenberry, Bradford Knapp, Jr., and Dr. R. T. Clark of the U.S.D.A. for making these data available.