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United States Department of Agriculture2
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.
1 Based on records of experimental herds cooperatively maintained by the United States Department of Agriculture and the Montana Agricultural Experiment Station. The authors acknowledge the helpful advice and assistance of Ralph W. Phillips and Bradford Knapp, Jr., in the planning of this study and in analyzing the data.
2 U. S. Range Livestock Experiment Station, Miles City, Montana.
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