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1. Non-genetically modified (non-GM) phytase product derived from Aspergillus niger possesses various side active enzymes including α-amylase, protease, cellulase and hemicellulase. In contrast, the product of genetically modified (GM) phytase product has much less side active enzyme since the capacity of phytase production is reinforced by gene modification. In the present study we have tried to determine whether the difference of side enzyme activity of phytase product affects growth performances and nutritive value in chicks; in addition we tried to characterise the physiological change induced by the difference of side active enzymes. 2. Single Comb White Leghorn male chicks at 7 d of age were fed on experimental barley-based diets for 10 d. The feeding trial was of a factorial design (3 × 2 × 2), having three types of dietary phytase products (control, non-GM or GM phytase products derived from A. niger at 1000 U/kg diet), two levels of dietary available P supplement (0 or 6 g/kg diet) and two levels of dietary protein (CP 180 or 120 g/kg). 3. The non-GM phytase product caused a 6% increase in final body weight and feed efficiency com6 pared with the control and the GM phytase product without interacting with dietary protein and available P level. However, in birds given available P-free diet, both non-GM and GM phytase products induced a 20% increase in plasma P concentration, suggesting no difference in phytase activity between the non-GM and GM phytase products. 4. The balance study showed that the metabolisable energy of the non-GM phytase product (15·6 ± 0·05 kJ/g diet) was significantly higher among the treatments (control, 15·1 ± 0·05; GM phytase product 15·3 ± 0·07). The non-GM phytase product also increased the rate of food passage through the crop, and caused a drastic reduction in intestinal weight, perhaps as a consequence of digestion of non-starch polysaccharides. 5. We conclude that the side active enzymes in non-GM phytase product improve growth performance and nutritive value of the diet in chicks. However, the efficacy of phytase activity should not be different between non-GM and GM phytase products. [ABSTRACT FROM AUTHOR]

1. The change in the rate of protein synthesis of different muscles, concentrations of plasma insulin, plasma insulin-like growth factor-I (IGF-I) and other plasma components were investigated after refeeding in fasted chicks. 5·2 g of the complete diet was refed. This was the maximum that could be force-fed with water. 2. The fractional synthesis rates (FSR) of breast (M. pectoralis major) and leg (M. gastrocnemius) muscles were measured after injection of L-\[2, 6-3H]phenylalanine. Plasma insulin and IGF-I concentration were determined by radioimmunoassay. 3. In the breast muscle, FSR was significantly reduced by 2-d fasting. The FSR had recovered completely after 1 h of refeeding and was maintained until 6 h. The change in FSR after refeeding was associated with the change in ribosomal efficiency (K[sub RNA]; absolute synthesis rate per unit RNA), while no change in ribosomal capacity (C[sub S]; RNA: protein ratio) was observed. 4. In the leg muscle, FSR was decreased by 2-d fasting and increased gradually toward 6 h after refeeding but did not reach the level of the fed control. In contrast to the breast muscle, no significant changes in C[sub S] and K[sub RNA] in the leg muscle were observed. 5. Plasma glucose concentration increased significantly at 1 h after refeeding but returned to the fasted level after 24 h. Plasma insulin concentration in chicks refed for 1 h was higher than in the fasted group. There was no significant change in plasma IGF-I concentration. 6. These results suggest that the FSR of breast muscle was more sensitive to refeeding than that of leg muscle which may be explained, in part, by differences in sensitivity to the change in circulating plasma insulin concentration after refeeding. [ABSTRACT FROM AUTHOR]

We investigated the influence of refeeding food-deprived chicks with either protein, carbohydrate, fat or combinations thereof on the rates of liver and muscle protein synthesis. After 2 d of food-deprivation, chicks were given individual or mixed protein, carbohydrate and fat. At 30 min after refeeding, the protein fractional synthesis rate (K(s)) was measured by a large dose injection of L-[2,6-(3)H]phenylalanine. When chicks were food-deprived for 2 d, liver K(s) was 67% lower and muscle fractional synthesis rate was half that of well-fed controls. Upon refeeding starved chicks a complete diet, K(s) in the liver and muscle returned to the level of fed controls within 30 min. When food-deprived chicks were refed protein alone or two of the three macronutrients, liver and muscle K(s) were significantly higher than those in the starved group. There was no effect of refeeding with carbohydrate or fat alone. Plasma glucose concentration was significantly greater than in fed or starved groups in chicks refed the complete diet, carbohydrate or carbohydrate mixed with either protein or fat. Refeeding chicks with the various macronutrients did not affect the plasma insulin or insulin-like growth factor-I concentrations. These results suggest that intakes of individual macronutrients additively increase liver and muscle protein synthesis and that the acute increase in muscle protein synthesis after refeeding chicks diets containing the three macronutrients was mainly regulated by the change in ribosomal efficiency. [ABSTRACT FROM AUTHOR]

1. We examined the influence of refeeding after 2 d of fasting on plasma insulin-like growth factor-I (IGF-I) concentration and hepatic IGF-I gene expression in chickens at 6 weeks of age. 2. Hepatic IGF-I mRNA was measured by ribonuclease protection assay and plasma IGF-I concentration was determined by radioimmunoassay. 3. Plasma IGF-I concentration decreased following fasting, increased to the level of fed controls after 2 h of refeeding but then fell back to the level of fasted chickens after 6 h of refeeding. 4. Fasting reduced hepatic IGF-I mRNA concentrations to less than half of those in the fed controls. Refeeding increased IGF-I mRNA sharply at 2 h after refeeding, but by 6 h after refeeding they had taller back again to levels significantly lower than at 2 h. 5. A significant correlation between plasma IGF-I concentration and hepatic IGF-I gene expression was found, suggesting that when chicks are refed after 2 d of fasting, the short-term increase in plasma IGF-I concentration may be partly regulated by the alteration in hepatic IGF-I mRNA. [ABSTRACT FROM AUTHOR]