Relationships among Definable Characteristics of Feeder Calves, Subsequent Performance and Carcass Traits. I. Objective Measurements

Three-hundred and forty-nine commercial calves of Angus, Hereford, Charolais-cross and Angus × Hereford classification were fed to an estimated constant subcutaneous fat thickness (12 mm) on high and medium energy diets. Physical description of the feeder calves, in terms of wither height, subcutaneous fat thickness (ultrasonic estimate) and body depth, combined with initial calf weight and breed classification, explained 54% of the variation in carcass weight within diet-year subclasses and 36% of that in days on feed. Initial weight was positively related (P<.001, partial b = .51) to carcass weight but unrelated (P>.10) to days on feed. Wither height was positively related to carcass weight (P<.001, partial b = 4.17) and days on feed (P<.001, partial b = 3.99) among calves on the high energy diet. Wither height was less highly related to carcass weight (P<.05, partial b = 1.54) and unrelated to days on feed (P>.10) among calves on the medium energy diet. Variation in initial fat thickness was negatively related to days on feed (P<.001, partial b = −13.26). The association between initial fat and carcass weight was negative (P<.001) and differed (P<.01) between the Charolais-cross (partial b = −23.26) and British breed groups (partial b's = −13.64, −8.02 and −12.53 for Angus, Hereford and Angus × Hereford, respectively). Body depth of calves was negatively related (P<.05) to carcass weight. Variation in yield grade was associated primarily with variation in adjusted fat thickness resulting from failure to slaughter all animals at the designated level of fat. Carcass quality grade was influenced by breed effects and days on feed.