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Calving Ease and Growth Rate of Simmental-Sired Calves. I. Factors Affecting Calving Ease and Growth Rate¹

Montana State University, Bozeman, 59717

Abstract

Field records from the American Simmental Association were used to study factors that affect calving ease and growth rate in Simmental-sired calves. Data were from 20,949 calves sired by purebred Simmental bulls. Each record contained the dependent variables, calving ease score, percent assisted births, birth weight, 205-day weight and average daily gain. Independent variables were management unit (herd weaning weigh date group), age of dam, sex of calf, percent Simmental of the calf (50 or 75%) and all two-factor interactions among fixed effects. In some analyses, calving ease score or birth weight were included as independent variables. All dependent variables were significantly affected by management unit, age of dam, sex of calf, percent Simmental, age of dam x sex of calf and age of dam x percent Simmental. When birth weight was included as a covariate in the analysis, sex of calf had no significant affect on calving ease score and percent assisted births. Regression of percent assisted births on birth weight indicated that percent assisted births increased 2.2% per kilogram increase in birth weight. However, from 2-year-old dams, percent assisted births increased approximately 4.5% and calving ease score .08 per kilogram increase in birth weight. Regression of percent assisted births on birth weight for calves from 3-, 4- and 5- through 8-year-old dams was not linear and indicated that the percent assisted births did not start to increase until birth weight reached 30 to 35 kilograms.

¹ Research supported in part by a grant from the National Association of Animal Breeders. Published with approval of the Director of the Montana Agricultural Experiment Station. Journal Series No. 767.

² American Simmental Association, 1 Simmental Way, Bozeman, MT 59715.