Effect of dietary restrictions and source of rats on growth rate and efficiency of conversion of food into muscles, bones and organs.

Abstract

Differences in weight of the body, six different skeletal muscles, epididymal fat pads, three different bones, spleen, heart, kidneys, testes and liver were observed in 21-day-old male Sprague-Dawley rats from two different suppliers. All rats were pair-fed a 10% casein diet ad libitum, 10%, 20%, 30% restricted for 4 or 8 weeks. Original body and tissue weight differences between the two strains of rats were maintained in all diets during the 4 and 8 week feeding periods. Trends in body and tissue weight changes due to dietary restriction were similar in both strains of rats. Diet restrictions for 4 or 8 weeks caused similar patterns of weight decrease in most tissues. Feed efficiency ratio (FER) was reduced significantly at the 20% and 30% restriction for 4 weeks only in the lighter strain of rats. FER was higher in the heavier strain than in the lighter strain of rats at all levels of diet restriction. Food conversion efficiency with reduced food intake was constant or decreased depending on the skeletal muscle studied; decreased significantly for epididymal fat pad, bone weight (one strain only), kidneys and liver (one strain only) with the 30% reduced diet for 4 weeks; and increased for bone length and testes weight. Therefore, significant deviations from ad libitum controls were found only at 30% diet restriction, and the wide differences in body and tissue weight of two strains of Sprague-Dawley rats did not affect the interpretation of results when fed the same restricted diets.