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Reduced and Compensatory Growth: Endocrine and Metabolic Changes during Food Restriction and Refeeding in Steers^1,2,

Institute of Animal Production, Swiss Federal Institute of Technology, 8092 Zurich, Switzerland ^* The Norwegian College of Veterinary Medicine, Department of Physiology, Oslo, Norway

Effects of food restriction, followed by refeeding, on energy and nitrogen metabolism, growth rates and blood levels of hormones and metabolites were studied in steers. During the restriction period, which lasted for almost 5 mo, allowance for energy and nitrogen were close to maintenance requirements. Heat production and growth rates were markedly lowered. In response to reduced food intake concentrations of thyroxine (T₄), 3,5,3'-triiodothyronine (T₃), insulin (IRI), glucose and -amino-acid nitrogen (AAN) were reduced, those of growth hormone (GH) and nonesterified fatty acids (NEFA) were elevated, whereas 3,3',5'-triiodothyronine (rT₃) and albumin were not different from levels measured in nonrestricted animals. During refeeding heat production and energy balances increased, nitrogen balances were transiently elevated and the animals exhibited compensatory growth. In response to refeeding, concentrations of T₄, T₃ and IRI increased within days. In contrast, GH decreased whereas rT₃ did not change. Within 2 d of refeeding there was a rapid fall of NEFA, and an increase of glucose, and ß-hydroxybutyrate within 2 and 12 d, respectively. The data demonstrate the ability of growing ruminants to adapt rapidly to variations in food intake by closely linked metabolic and endocrine changes, which are associated with shifts in energy and nitrogen metabolism and, finally, by reduced or compensatory growth.

KEY WORDS: • growth • compensatory growth • energy intake • hormones • metabolites

¹ This study was supported by a grant (0.330.077.65/2) from the Swiss Federal Institute of Technology, Zurich, Switzerland.

² The experiments, particularly the studies on energy and nitrogen metabolism, were performed by W. Schnyder in fulfilment of the requirements for Doctor of Science in Technology (in preparation). Data of hormones and metabolites have in part been presented by the first author at the 5th International Symposium on Ruminant Physiology, Clermont-Ferrand, France, September 1979. Some results on energy metabolism have been presented by W. Schnyder at the 9th Symposium on Energy Metabolism in Farm Animals in Lillehammer, Norway, September 1962.

Manuscript received 17 May 1984.