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Effect of Uterine Horn Pregnant, Parity of Dam and Sex of Calf on Birth Weight and Gestation Length in Angus and Shorthorn Cows^{1, 2,}

University of Wisconsin, Madison

Abstract

Records on 128 gestations from 48 Angus cows and 72 gestations from 35 Shorthorn cows were studied by standard partial regression and analysis of variance. Tests were made for effects of parity of the dam, sex of the calf, breed, and uterine horn pregnant in the dam on birth weight and gestation length.

The standard partial regression of birth weight on parity was highly significant for both the Angus and Shorthorn breeds (0.43 and 0.34, respectively). The corresponding value for gestation length was significant for the Angus (0.20) but not for the Shorthorn ( —.05). The standard partial regression of birth weight on sex of the calf was significant in the Angus breed (0.17). The standard partial regression of birth weight on sex in the Shorthorn breed was 0.15 which was not significant. Gestation length was not significantly affected by the sex of the calf in the Angus breed (b'=0.10), but female Shorthorn calves were gestated significantly longer than males (b'=–.33, P<0.01). After birth weight and gestation lengths were adjusted for parity and sex it was found that Shorthorn calves averaged 4 lb. heavier at birth than Angus calves (P<0.01) while the average Angus gestation length was 6.8 days longer than that of the Shorthorn breed (P<0.01). Uterine horn pregnant had no significant effect on either birth weight or gestation length over both breeds. No significant interaction between the effects of breed and uterine horn on birth weight was found. The interaction of these effects on gestation length, however, was significant (P<0.05).

¹ Paper from the Department of Genetics No. 751 and the Department of Animal Husbandry, published with the approval of the Director of the Agricultural Experiment Station.

² Study supported in part by funds allocated on the recommendation of the North Central Technical Committee on Beef Cattle Breeding (NC1).