Growth and Composition of the Empty Body in Steers of Different Maturity Types Fed Concentrate or Forage Diets

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Abstract
One hundred and ninety feeder steers comprised of 64 small rotational crossbreds (mainly Hereford crosses), 66 large rotational crossbreds (mainly Charolais and Simmental crosses) and 60 Holsteins were fed either a concentrate diet of corn silage and high moisture corn or a forage diet of corn silage and alfalfa haylage. All steers were fed ad libitum, weighed every 28 d and slaughtered to cover a range of external fat thickness (0 to 15 mm) determined ultrasonically for each treatment. Steers were removed from feed 36 h and water 16 h before slaughter. Internal organs, visceral fat depots (including kidney and pelvic fat), components of the emptied digestive tract and other noncarcass parts (head, hide and feet) were weighed in the abattoir. One side from each carcass was physically separated into depot fat, lean and bone. When comparisons were made at the same degree of external fatness, large rotational crossbreds had the highest proportion of warm carcass weight relative to empty body weight, while Holsteins had the lowest. Large rotational crossbreds had significantly lower proportions of body organs (liver, lungs, kidneys), noncarcass parts (head, hide) and digestive tract components (rumen, omasum, abomasum, small and large intestines) relative to empty body weight than small rotational crossbreds. Holsteins had the lowest proportions of hide, but the greatest proportions of their empty bodies as body organs (spleen, heart, liver, lungs, kidney), visceral fat depots (caul, mesenteric, kidney and pelvic), components of the digestive tract and noncarcass parts (head and feet). There were no differences in the proportion of carcass weight relative to empty body weight for animals fed concentrate or forage diets. However, animals fed concentrate diets had a greater proportion of their empty bodies as liver, lungs and visceral fat and a lower proportion as head, hide, feet and components of the digestive tract than animals fed forage diets. Warm carcass weight and empty body weight increased at a similar rate. The body organs and digestive tract became a lower proportion of empty body weight gain, whereas the visceral fat depots became a higher proportion of empty body weight gain as empty body weight increased. Copyright © 1985. American Society of Animal Science. Copyright 1985 by American Society of Animal Science

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