Suppressed development of edible portion in carcasses from cattle fed hay during the early feeding period (216-340 kg live weight) was followed by compensatory growth during the intermediate (341-409 kg live weight) and final (410-454 kg live weight) periods. However, when silage in the early feeding period was followed by corn concentrate in the intermediate period, no increased 'edible portion' development was achieved beyond that produced by continuous silage. The final feeding period (corn concentrate) resulted in a decline in ' edible portion' percentage in cattle that previously received concentrate in the intermediate period whereas those that previously received silage remained at about the same percentage.Cattle fed hay during the early period had less (P < 0-01) carcass weight, less (P< 0'01) fat cover, and more (P < 0-01) reticulo-rumen weight than those fed corn silage for the same period, regardless of slaughter weight.In the heavy (409 and 454 kg) slaughter groups, cattle fed silage in the early period had higher (P < 0-05) marbling scores than those fed hay. Feeding silage in the intermediate period resulted in lower colour (P < 0-01) and firmness (P < 0-01) scores in the longissimus dorsi muscle than feeding concentrate at that time. The dietary regimes used in these studies resulted in widely varying growth rates among treatments with consequential differences in the average age of the animal groups at slaughter. Therefore, the treatment effects observed seem to be easily explicable on the basis of age differences.

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Studies were conducted on the quantity and distribution of fat in 104 half-sib Angus steers which had received various combinations of hay, corn silage, and corn concentrate. Groups were slaughtered at live weights of 216, 284, 340, 409, and 454 kg. The weights of mesenteric, cod, pelvic, kidney and total excess carcass fat were determined. Four linear measurements of subcutaneous fat, three cross-sectional area measurements of intermuscular fat, and the intramuscular fat in seven muscles were observed. The results showed that the feeding regimes had marked influences on the quantity and location of fat, particularly during the early feeding period (216-340 kg live wt.). Feeding hay during this period generally resulted in less fat deposition than feeding corn silage, but the suppression of intramuscular fat deposition was not evident until the animals were subsequently fed higher energy rations to heavier weights (409 and 454 kg). The results indicated that it may be possible to design dietary regimens that suppress waste fat but allow intramuscular fat to be deposited.The results described above imply that one might influence the deposition of intramuscular fat by proper design of the diet in the early feeding period. Although this possibility exists, it is noted that quantities of chemically extractable fat are not identical with quantities of marbling fat and hence changes in the former may not alter the visible quality of the meat.

SUMMARYThe effects of several dietary regimens on the fat-free mass and the dry-matter, ash and potassium-40 content of selected bovine muscles were estimated. Muscle data from 104 half-sib Angus steers were secured at several stages of growth and after several feeding regimens. The results indicated that a hay diet, by comparison to a higher energy silage diet in the early feeding period (216–340 kg live weight), suppressed the fat-free weight, reduced the dry-matter content and increased the ash content of several muscles. These effects of early diet were reversed, however, when the animals were subsequently fed higher-energy rations and slaughtered at heavier weights (409 and 454 kg live weight). Data on potassium-40 gamma emissions by composite muscle samples confirmed the existence of age- or weight-associated decreases and suggested possible dietary influences on potassium levels in bovine muscles. The trends in these data indicated that low dietary energy (hay feeding) in the early feeding period delayed the decline in muscle potassium that normally accompanies maturation.

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