Comparison between constant-protein, calorie-restricted and protein-restricted, calorie-restricted diets on growth, in vitro lipogenesis and plasma growth hormone, thyroxine, triiodothyronine and somatomedin-C (Sm-C) of young chickens
Rosebrough, R.; Mcmurtry, J.; Proudman, J.; Steele, N.
Comparative Biochemistry and Physiology. A Comparative Physiology 93(2): 337-343
1. We studied the effects of calorie-restricted, constant-protein and calorie-restricted, protein-restricted diets on growth and in vitro metabolism of male chickens from select (Cobb Line 500) and byproduct (Cobb female line) lines of broiler chickens. 2. Chickens consumed 40, 60, 80 or 100% of a prescribed formula for dietary energy (body weight in g0.0 .times. 16.7 kJ) in the presencr of set (CEP) or varied dietary protein (VEP). 3. Chickens fed VEP were heavier (P < 0.05) at all energy intakes than chickens fed CEP. Slope analysis of data for in vitro lipogenesis showed a significant difference between the two treatment series. 4. Plasma growth hormone was inversely related (P < 0.05) to Sm-C. Growth hormone levels were greater in chickens on a low plane of energy nutrition (40%) than on the maximum plane (100%). 5. Plasma Sm-C levels (pooled across energy series) were greater in the select than in the byproduct line. There were no differences in plasma T3 between the two lines. There was a significant increase (P < 0.05) in T3 and a decrease in the T4/T3 ratio accompanying in increase in dietary energy. 6. Restricting dietary carbohydrate and protein compromises anabolic processes more than restricting carbohydrate alone.