Growth of Replacement Heifers on Shortgrass Ranges of Colorado

Abstract

We examined records of young cattle produced on shortgrass range in Colorado to evaluate the problem of inadequate growth of replacement heifers-a problem that forces ranchers to delay first calving until heifers are 3 years old. Weaning weights of calves produced on 44 ranches did not increase from 1950 through 1970 in spite of improved breeding practices. Hence, summer range conditions may limit growth of heifer calves. Weaner heifers gained an average of only 0.4 lb/head/day during their first winter. Whereas, to be large enough for successful breeding, heifers should gain 1.2 lb/head/day. March, April, and May forage conditions were identified as critical to reproduction of cattle because of inadequate herbage, poor quality of old herbage, excessive energy expenditure in the search for scarce green herbage, teeth shedding by 2-year-old heifers, and increased nutritional needs for milk production and readiness to breed. The data identify two criteria for attaining a goal of successful breeding of yearling heifers raised on shortgrass range: (1) place all brood cows, especially 2-year-old heifers with first calf, on gain-promoting forage and feed in March, April, and May, and (2) increase winter daily gain of weaner heifers by at least 0.83 lb. Research is needed to determine if these criteria can be attained profitably.