RESPONSE OF MALE AND FEMALE WEANLING RATS TO DIETS OF DIFFERENT DIGESTIBLE ENERGY CONCENTRATIONS AND TO SUPPLEMENTATION WITH VITAMIN E, USING BARLEY OR WHEAT AS CEREAL SOURCES

Sixty-four weanling rats were used in an experiment lasting 6 weeks to test the response of male and female rats to diets having 2.8, 3.0, 3.2, and 3.4 Mcal digestible energy (DE) per kg, where barley and wheat were used as the cereal sources and diets were supplemented with 22 IU vitamin E/kg or unsupplemented. The use of wheat or barley did not influence the performance of female rats but males utilized barley-based diets better than wheat diets and gained more in some weeks, though not overall. Male rats did not respond to vitamin E supplementation but females consumed more of the vitamin E-supplemented diets and grew 6% faster (P < 0.10). Except in the 1st week, females ate more of the lower energy than of the higher energy diets and so DE concentration did not influence rate of gain. Males were not able to adjust food intakes to compensate for dietary energy levels and needed a DE concentration of 3.2 Mcal/kg diet for maximum growth. The data indicate that there is a sex difference in growing rats insofar as DE concentration of the diet required for maximum gain is concerned.