Effects of Season of Breeding on Reproductive and Weaning Performance of Beef Cattle Grazing Seleniferous Range

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Abstract
The effect of season of breeding on reproductive and weaning performance was studied over a 5-year period in which 152 matings were made. The numbers of matings made in each breeding group were 75 in the early group (bulls turned out approximately May 1) and 77 in the late group (bulls turned out approximately July 18). The early breeding group averaged a 22.3% higher calf crop born, with the early group averaging 60.0% and the late group 37.7%. The advantage to the early breeding group in percent weaned was 19.6, with the early group averaging 52.0% and the late group 32.4%. Weaning weight unadjusted for age of calf averaged 60 lb. in favor of the early group, but after age adjustment no significant difference existed between the two groups. No season effect was found for conformation, condition, or selenium symptoms at weaning. The results indicate an advantage to calving early if selenium poisoning is a problem and early calves can be properly cared for.