Charolais and Angus Steers Slaughtered at Equal Percentages of Mature Cow Weight. I. Effects of Slaughter Weight and Diet Energy Density on Carcass Traits

Abstract

Fifty-six Angus and 56 Charolais steers were evaluated for the effects of breed, slaughter weight and diet energy density on feedlot and carcass traits. Eight calves of each breed were slaughtered at the start of the experiment. Forty-eight steers of each breed were assigned for slaughter at 86 (light), 100 (middle) or 114% (heavy) of mean mature cow weight (Angus = 476 kg, Charolais = 612 kg). Diets of corn silage, corn and soybean meal were fed ad libitum; the diets contained 12.5% crude protein and either (1) 2.72 or (2) 2.96 Meal metabolizable energy (ME)/kg dry matter. Mean off-test weights were 267, 409, 472 and 5 34 kg for Angus and 270, 516, 602 and 681 kg for Charolais (initial, light, middle and heavy groups, respectively). Average daily gain (ADG) for both breeds decreased (P<.01) as weight increased, but ADG of Angus and Charolais did not differ from each other. Feed conversions (kilograms diet per unit weight gain) for the breeds were similar. Although light Angus had higher (P<.01) quality grades than light Charolais (∼average versus ∼low Choice), grades did not differ between needs at other weights. Breeds did not differ in longissimus muscle fat content at any assigned weight class. Fat thickness increased (P<.01) for both breeds as weight increased and was greater (P<.01) for Angus within each weight class. Although the higher ME diet (2) did not improve ADG or marbling for either breed, Angus fed diet 2 had greater (P<.05) mean fat thickness and lower (P<.05) carcass cutability than Angus fed diet 1. Angus fed either diet had lower (P<.01) cutability than Charolais. Steaks from Angus carcasses had higher (P<.01) average sensory panel flavor and juiciness ratings than did those from Charolais at the light weight, but sensory panel means did not differ at other weights. Low Choice longissimus muscle fat content (∼4.3%) was attained at shrunk body weights of 368 kg for Angus and 464 kg for Charolais. Copyright © 1981. American Society of Animal Science . Copyright 1981 by American Society of Animal Science.