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US Department of Agriculture, Miles City, MT 59301 and Fort Collins, CO 80521 and , and Colorado and Montana Agricultural Experiment Stations, Cooperating
Abstract
Records on 140 individually fed cow-calf units at weaning and 137 units at slaughter were used to determine relationships between actual measures of biological cow-calf unit efficiency at weaning and slaughter and predictive measures of efficiency at those end points. The relationships among actual measures of efficiency and several traits of the calf and cow were also investigated. Data were collected at the Livestock and Range Research Station, Miles City, Montana. In this study, TDN intake of a cow was adjusted to 1 yr and of a calf from birth to 180 d of age; FEFF WEAN is defined as 180-d calf weight divided by TDN intake of the cow and calf for these periods. Predictive measures of efficiency accounted for 66 to 76% of the variation in biological efficiency of the cow-calf unit at weaning. Preweaning average daily gain and 180-d calve weight each accounted individually for 69% of the variation in cow-calf unit efficiency at weaning. Two measures of biological efficiency of the cow-calf unit at slaughter were studied. The first, FEFF LIVE, measured kilograms of live calf weight produced/kilogram of TDN consumed by the cow during the year and by the calf from birth to slaughter. Predictive formulas for this measure accounted for 41 to 56% of the variation in efficiency at slaughter. The correlation between this measure of efficiency and average daily gain from birth to slaughter was .75. The second measure of efficiency at slaughter, FEFF CARCASS, was defined as weight of lean cuts produced divided by TDN intake of the cow during the year and of the calf from birth to slaughter. Predictive formulas for this measure accounted for 49 to 66% of the variation in cow-calf unit efficiency at slaughter. Weight of lean cuts/day of age also accounted for 66% of the variation in FEFF CARCASS. The best predictive measures of cow-calf unit efficiency at weaning and slaughter included measures of metabolic calf weight and(or) cow weight in the denominator as a reflection of nutrient requirements of the cow-calf pair. However, when evaluated within a breed group, measures of growth rate seemed to be as useful as the best predictive measures in predicting cow-calf unit efficiency. These results are supportive of the methods used in performance testing programs to improve productivity and efficiency of beef production. Within a group, no significant associations between measures of mature cow size and efficiency of the pair at weaning were found. A small negative relationship was evident at slaughter. Cow-calf units with steer progeny were 5.4% more efficient at weaning than units with heifer progeny and were 5.9 and 7.7% more efficient based on the two measures of efficiency at slaughter.
1 This research was conducted at the Livestock and Range Research Station, Miles City, MT, and supported in part by Colorado Agr. Exp. Sta. and published as Journal Series No. 2792. Montana Agr. Exp. Sta., Journal Series No. 1376
2 Present address: West Virginia Univ., Morgantown 26506
3 Colorado State Univ., Fort Collins 80523
4 Livestock and Range Research Station, USDA, ARS-WR, Miles City, MT 59301
5 Biometrical Services, USDA-ARS, Fort Collins, CO 80521.
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