Fertility of Range Beef Cattle1

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Abstract
A study of the breeding and calving records at the U. S. Range Livestock Experiment Station, Miles City, Montana, was made on 4,753 cow years over an 18-year period. The average calf crop was 83.1 per cent. The effect of yearly variations due chiefly to environmental causes was statistically significant. Analysis showed that there was not a significant effect of age of cow on fertility. It was shown that over 50 per cent of the shy breeding cows could be identified by the time they reach 4 years of age and approximately 80 per cent by 6 years of age. Reactors to brucellosis and deaths on the range were more numerous in the 3- to 6-year-old age than in the 7- to 11-year-old group. There was a highly significant difference between bulls in per cent calf crop and a variation from 45.5 to 94.0 per cent was observed. Age of bull did not have a significant effect on calf crop percentage but the older bulls lost increasingly more weight during the breeding season. In a study comparing single and multiple bull breeding units, single bull herds had approximately 6 per cent more calves than multiple bull herds. Recommendations to the range cattle producer are proposed that should aid in raising the calf crop percentage on his range.

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