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Charolais and Angus Steers Slaughtered at Equal Percentages of Mature Cow Weight. II. Empty Body Composition, Energetic Efficiency and Comparison of Compositionally Similar Body Weights

1981; Oxford University Press; Volume: 53; Issue: 4 Linguagem: Inglês

10.2527/jas1981.534898x

1544-7847

K. A. Barber, L. L. Wilson, J. H. Ziegler, P. J. LeVan, J. L. Watkins,

Agriculture Sustainability and Environmental Impact

Fifty-six Angus and 56 Charolais steers were evaluated to determine effects of breed, slaughter weight and dietary energy density on empty body (EB) composition and energetic efficiency and to compare breeds at compositionally similar body weights. Eight calves of each breed were slaughtered at the start of the experiment. Forty-eight steers of each breed were fed diets containing an estimated 2.72 or 2.96 Mcal metabolizable energy (ME)/kg dry matter; the diets were composed of corn silage, corn grain and a protein, vitamin and mineral supplement. The steers were slaughtered at 86 (light), 100 (middle) or 114% (heavy) of breed average mature cow weight (Angus, 476 kg; Charolais, 612 kg). Forty-seven Angus steers completing the feedlot phase had a mean initial age and weight of 300.9 days and 264.8 kg; 43 Charolais steers had a mean initial age and weight of 284.9 days and 275.6 kilograms. Mean EB weights at slaughter were 231.2, 354.7, 418.2 and 485.6 kg for Angus (in the initial, light, middle and heavy slaughter groups, respectively; P<.01) and 239.8, 457.9, 540.1 and 617.7 kg for Charolais. EB fat content increased (P<.01) within each breed with increased slaughter weight. Light, middle and heavy Angus steers deposited 41.0, 44.4 and 43.8%, respectively, of their EB gain as fat. Despite slaughter at heavier body weights and at percentages of mature dam weight comparable to those for Angus, corresponding Charolais groups deposited 36.3, 37.3 and 39.2%, respectively, of their EB gain as fat (breed differences, P<.01). The increase in dietary energy from diet 1 to diet 2 resulted in greater (P<.01) EB fat deposition for Angus, but not for Charolais. For Angus fed diet 1, EB gain from 231.2 to 354.7 kg (39.1% fat) was compositionally similar to Charolais EB gain from 239.8 to 617.7 kg (39.2% fat). Despite these differences in rate of fattening, final EB composition for Angus and Charolais slaughter groups differed (P<.01) only at the middle weight. Comparable EB fat content (30%) was attained by Angus steers at 455 kg (diet 1) and 431 kg (diet 2) shrunk body weight and by Charolais steers at 619 kg (diets 1 and 2) shrunk body weight.