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Effects of Body Size on Kinetics of Glucose Metabolism and on Nitrogen Balance in Growing Cattle^1,2,

Nutritional Physiology Group, Department of Animal Science, Iowa State University, Ames, IA 50011

Effects of body size on the kinetics of glucose metabolism were examined. In trial 1, steers were fed 6 kg of an 80:20 concentrate:roughage diet daily across a weight range of 226 to 470 kg. In trial 2, steers were fed 4.5 kg of a 45:55 concentrate:roughage diet daily across a weight range of 134 to 390 kg. Glucose irreversible loss averaged 820 ± 32 and 461 ± 13 mg/min for trials 1 and 2 and was not affected by body size. Thus, glucose irreversible loss seems to be regulated by feed intake when intake is above maintenance. Body size had no effect on glucose total entry rate, recycling or pool size. Blood glucose concentration and glucose space decreased at 0.004 mg · ml^-1 · kg^-1 and 0.002 fractional units body wt · kg^-1 as body size increased. Digestible energy and nitrogen balance were measured in trial 2. Digestibility of energy increased at 0.0054 Mcal · d^-1 · kg^-1 as body size increased. Nitrogen retention averaged 28.2 g · d^-1 and was not influenced by body size even though energy intake approached maintenance amounts at the end of the trial. On the basis of urinary nitrogen excretion data, we conclude that the maximum net contribution of amino acid carbon to glucose synthesis was 8% of glucose carbon.

KEY WORDS: • body size • glucose • metabolism • nitrogen balance • cattle

¹ Journal Paper No. J-10793 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Projects No. 2506 and 2389. Supported in part by funds provided by PHS/NIH Grant AM-10706 and by USDA Grant 901-15-160. Results of Trial 2 are from a thesis submitted by Leon Moss to partly fulfill requirements for the M.S. degree at Iowa State University. A report was presented at the 75th Annual Meeting of the American Dairy Science Association; see (1980) J. Dairy Sci. 63 (Suppl. 1), p. 86 for abstract.

² Address reprint request to: J. W. Young, Dept. of Animal Science, Iowa State University, Ames, IA 50011.

³ Present address: Dept. of Animal and Dairy Sciences, Auburn University, Auburn, AL 36849.

⁴ Present address: 4019 East 23rd Street, Des Moines, IA 50317.

Manuscript received 19 February 1985. Revision accepted 1 July 1986.

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