Protein synthesis and degradation after acclimation to different environmental temperatures and energy intakes

1. 1|The influence of environmental temperature and energy intake on protein synthesis and degradation has been examined in young pigs acclimated to 35 or 10°C on a high (H) or low (L) energy intake (H = 2L). Measurement were made at thermal neutrality in relation to bot skeletal muscle and the whole body, using [3H]tyrosine. 2. 2|Tyrosine catabolic rate per unit body weight was significantly greater in animals from the cold than the warm (P < 0.02). However, there were no statistically significant differences in relation to fractional rates of muscle or whole body protein synthesis. Estimates for muscle were markedly influenced by whether intracellular tyrosine or plasma tyrosine was assumed as precursor. 3. 3|Differences in initial growth rate were observed since animals at 10°C needed energy for thermoregulation and those at 35°C did not. The differences in body size which developed led t a fixed amount of food representing a greater energy supply per unit body weight in the cold than the warm. Thus, although both groups synthesized protein at the same fractional rate, for those in the cold more amino acid was available for catabolism.