Yuichiro Tomita

Effect of environmental temperature on muscle protein turnover and heat production in tube-fed broiler chickens

The present experiments were undertaken to investigate the effects of environmental temperatures on growth, abdominal fat content, rate of muscle protein turnover, and heat production in tube-fed intact male broiler chickens. Plasma concentrations of thyroxine (T4), triiodothyronine (T3), and corticosterone (CTC) were also examined. Chicks (15 d old) were kept at different environmental temperatures (16, 19, 22, 25, 28, 31, and 34 degrees) and given the experimental diet (200 g crude protein/ kg, 13.57 MJ/kg metabolizable energy) by tube three times daily throughout the 12 d experimental period. In the hot conditions, except for 34 degrees, body-weight gain was significantly higher than in the cold conditions. Thus, food conversion ratios (food:gain ratios) were lower when the birds were exposed to the hot conditions other than 34 degrees. Likewise, abdominal fat content was significantly increased, and heat production was lower in the groups kept under the hot conditions other than 34 degrees. The rate of skeletal muscle protein turnover and plasma concentration of CTC were decreased when the birds were exposed to hot conditions other than 34 degrees, suggesting a role of CTC in the regulation of muscle protein turnover. Plasma concentrations of T4 and T3 were significantly decreased as environmental temperature increased. These results clearly show that plasma concentrations of thyroid hormones and CTC are associated with accelerated muscle protein turnover and heat production.

The rate of degradation of myofibrillar proteins of skeletal muscle in broiler and layer chickens estimated by N-methylhistidine in excreta

After N tau-methylhistidine (N tau-MH) distribution among the various organs or the tissues was determined in male broiler chickens of 15 d of age, the rates of degradation of myofibrillar proteins in male layer and broiler chickens at different stages of growth were determined by means of N tau-MH. About 75 and 8% of the total N tau-MH in the tissues occurred respectively in skeletal muscle and stomach, and most of the remainder in the intestine and the skin. The rates of degradation of myofibrillar proteins in the male layer and broiler chickens of 21, 42 and 63 d of age were calculated to be 6.1, 4.5 and 2.4%/d (layer) and 5.0, 2.8 and 0.9%/d (broiler) respectively. These calculations involve the assumption that 80% of the total excreted N tau-MH was derived from skeletal muscle. The results strongly indicate that the rapid growth of the broiler chicken is facilitated by the reduced rate of protein degradation.

Effects of dietary corticosterone and trilostane on growth and skeletal muscle protein turnover in broiler cockerels

1. The effects of dietary corticosterone and trilostane, an inhibitor of glucocorticoid synthesis, on: growth, rates of synthesis and breakdown of skeletal muscle protein, and content of abdominal fat were studied in broiler chickens. 2. Dietary corticosterone (5, 10 or 20 mg/kg) depressed body weight gain and increased abdominal fat content in a dose-dependent manner while dietary trilostane (1.4 or 7.0 mg/kg) had no effect. 3. The rate of protein breakdown in skeletal muscle estimated from N tau-methylhistidine excretion was increased in a dose-dependent manner by dietary corticosterone but it was decreased by trilostane. 4. The rate of skeletal muscle protein synthesis was not affected by corticosterone although it was decreased by trilostane. 5. Plasma corticosterone concentration was increased in a dose-dependent manner by dietary corticosterone and decreased by treatment with 7 mg trilostane/kg diet. 6. The results indicate that higher concentrations of plasma corticosterone increase protein breakdown in skeletal muscle but do not affect muscle protein synthesis while both the rates of synthesis and breakdown are decreased when plasma corticosterone concentration is reduced.

Dietary protein level alters oxidative phosphorylation in heart and liver mitochondria of chicks.

To determine the effects of dietary protein level on cardiac and hepatic mitochondrial oxidative phosphorylation, chicks were fed on semi-purified diets of different protein levels (7, 25, 43 and 61% of metabolizable energy content) for 7, 14 and 21 d. All diets were formulated to contain equivalent fat, mineral and vitamin contents on a gross energy basis. Cardiac and hepatic mitochondrial oxidative phosphorylation rates were assessed polarographically with pyruvate and malate as substrates. Cardiac mitochondria isolated from chicks fed on a 43 or 61% protein-energy diet for 7 d exhibited significantly reduced ADP:oxygen (ADP:O) ratios when compared with mitochondria isolated from chicks fed on a lower-protein-energy diet. Feeding low- (7%) protein-energy diets for 14 d resulted in a relatively increased ADP:O ratio in the heart. Responses of ADP:O ratios to protein level in hepatic mitochondria showed more dependency on protein level than in heart muscle; at all feeding periods the ADP:O ratio decreased with an increase in protein level. As a result, ATP synthesized in the liver, expressed as nmol/mg mitochondrial protein per min, significantly decreased with increased dietary protein level. A parallel correlation was observed, in chicks fed on diets with different levels of protein, between ADP:O ratio for liver mitochondria and body fat. These results suggest that the reduction in oxidative phosphorylation in the heart and liver of animals fed on a higher protein-energy diet may partly contribute to the depression of body fat.

Response surface analyses of the effects of dietary protein, fat and carbohydrate on feeding and growth pattern in mice from weaning to maturity

Responses of gross energy intake and body weight of mice from weaning to maturity to dietary composition of energy-yielding nutrients were studied. Twenty-four groups of ddY male mice were fed for 70 days purified diets with a range of 0·08 to 0·75 protein, 0 to 0·92 fat and 0 to 0·92 carbohydrate concentration, calculated on a gross energy basis. Food intake and body weight data in each group were analysed by non-linear regression to obtain values of the parameters in the feeding and growth equation of Parks (1982). Prediction equations for these parameters were obtained with mixture model forms as a function of dietary protein, fat and carbohydrate. These equations for the parameters were then used to construct the response surfaces of body weight and growth rate at a given time on a triangular graph. The response surfaces of body weight at any time were convex, peak positions of which shifted from 043 protein and 0·29 fat at 10 days to 0·36 protein and 0·52 fat at 70 days. The configuration of response surfaces of growth rate (dW/dt) to the three components depends on feeding periods and at the longer periods of feeding the convex configuration of the surfaces became planar. The response surfaces of food efficiency (dW/dF) at any age were almost parallel to those of dW/dt, whereas a parallelism was observed between response surfaces of dW/dt and dF/dt only in young animals. These results suggested that the responses of body weight in young animals to dietary composition of energy-yielding nutrients depended on those of daily energy intake as well as food efficiency, but that those in older animals were affected by food efficiency only.

Response surface analyses of the effects of dietary fat on feeding and growth pattern in mice from weaning to maturity

Responses of gross energy intake and live weight of mice from weaning to maturity to dietary fat level were studied. Six groups of ddY male mice were given purified diets covering the range (0 to 70%) of fat concentration on a gross energy basis for 72 days. The food intake and live weight data in each group were analysed by non-linear regression to obtain values of the six parameters in Parks feeding and growth equations. These parameters, found as a function of the fat content of diet, were then used to construct the response surfaces of food intake and live weight over the dietary fat v. age space. The daily energy intake rose rapidly with age to a plateau at about 7 to 14 days after weaning and was maintained throughout the experiment, independent of the dietary fat content. Live weight as a function of time after weaning increased to a plateau at every dietary fat level, but the details of the pattern of growth were affected by the dietary fat level. After about 30 days of feeding, the higher the fat content of the diet, the greater the gain in live weight. Apparent digestibility of dietary energy decreased with an increase in fat content, especially in the early period.