Effects of Ad Libitum, Maintenance and Sub-Maintenance Feeding and of Compensatory Growth on some Biochemical Properties of Muscle from Weanling Rabbits

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Abstract
Weanling male rabbits were fed either: 1) a complete diet ad libitum (control); 2) a maintenance diet; or 3) a sub-maintenance diet. After 20 days, half of each group was slaughtered and the remainder was placed on treatment 1 until they achieved the same body weights as the controls (about 30 more days), when they were also killed. Body organs, including livers, hearts, lungs and kidneys, were significantly reduced in weight by nutritional stress. Maintenance and sub-maintenance feeding resulted in increases in ultimate muscle pH, water content and alkali-soluble and -insoluble stromal proteins. The intracellular proteins, especially the myofibrillar fraction, decreased markedly, depending on the degree of nutritional stress. Swelling of the stromal proteins was less for the underfed rabbits, indicating that nutritional stress increased the number of acid-stable cross-linkages. Calcium-induced contraction was not effected by any of the nutritional treatments. Blood enzymes were not affected by nutritional stress from the standpoint of their multiple molecular forms, mobility or band profiles. All differences in muscle characteristics disappeared during compensatory growth except for the increased amount of alkali-insoluble stroma protein. The concepts of labile, mobilizable and fixed body proteins are discussed.