1. Heavy-breed (HB) chicks differed from light-breed (LB) ones in their propensity to be overfed. Whereas in the LB chicks the amount by which they could be overfed reached 70 % more than the food consumed daily by the ad lib.-fed chicks, in the HB chicks the maximal excess was only 13 %. 2. Overfeeding caused a slight but statistically significant increase in the linear growth rate (shank length) of the LB chicks, with an opposite effect in the HB chicks. 3. Overfeeding increased the weight of the crop, proventriculus, small intestine, pancreas, liver and adipose tissue but had no such effect on the heart, cerebrum or cerebellum. 4. Overfeeding had no effect on the specific activities of the pancreatic digestive enzymes, liver xanthine dehydrogenase, or tryptophan oxygenase (EC 1.13.1.12). The increase in the total activities was due entirely to organ hypertrophy. 5. Obesity induced in young chicks had no residual effects on the adult LB chicks, but reduced the linear growth of the adult HB chicks. 6. An explanation for the difference between breeds in response to overfeeding at an early age is discussed.

The relative weights of the gastro-intestinal segments and of some other internal organs from light and heavy breed chicks from hatching to 21 days of age were compared. 2. The relative weight of the duodenum and jejunum was higher in the light breed than in the heavy one, the reverse relationship was found for the ileum and caecum. 3. The relative growth of the pancreas, heart, cerebrum and cerebellum was greater in the light breed.

Canavanine sulphate in the diet significantly retarded larval growth and at the highest concentration used (36 m-mole/kg diet) induced a very high mortality. No other arginine derivative tested had a comparable effect. At concentrations of 1.8 m-mole/kg diet or more, canavanine sulphate inhibited larval arginase activity. In vitro arginase inhibition by canavanine sulphate was almost linear, with total inhibition at 10 mM. Comparable inhibition was observed with chick kidney, human erythrocyte and sheep erythrocyte arginases. Tribolium arginase is activated by low concentrations of Mn2+ and has an apparent Km of 20 mM. It is rapidly inactivated in the absence of substrate.

1. Excessive amounts of food (70% greater than ad lib . intake) introduced into the gastrointestinal tract of young chicks were efficiently digested and caused increased growth resulting mainly from lean body substance and partially from fat deposition, more efficient energy utilization than the ad lib .-fed controls, increased relative weights of the crop, proventriculus, intestine, liver and abdominal adipose tissue. Pancreas relative weight was not changed and that of the gizzard was reduced. 2. The treatment also caused changes in blood plasma composition. Free fatty acid, trigly-ceride, α 2 -, β- and γ-globulin and pre-β-lipoprotein concentrations increased. 3. Fasting for 30 h caused higher body fat losses and lower body protein losses in the force-fed chicks than in the ad lib .-fed chicks. 4. The effects of over-feeding on body and blood plasma composition and differences found in these measurements during starvation are discussed.

1. Force-feeding of young chicks for 15 d increased kidney arginase ( EC 3·5·3·1) activity threefold. Fasting for 30 h decreased this activity by 50%. 2. Liver xanthine dehydrogenase was slightly increased after force-feeding and decreased following fasting. 3. The specific activities of two pentose-phosphate-cycle enzymes were not significantly affected by force-feeding, but glucose-6-phosphate dehydrogenase ( EC 1.1.1.49) decreased following fasting. 4. The over-all secretion of digestive enzymes increased parallel to the increase in food consumption. Therefore, despite an increased absolute weight of the pancreas and intestinal chyme, specific activities were the same in the force-fed and ad lib .-fed groups, except for a higher activity in intestinal amylase. 5. Fasting did not affect the pancreatic enzymic activities.

Digestive and metabolic enzymes were studied in geese in which fatty livers and obesity were produced by forced feeding. The effect of different protein levels before and after the forced feeding period was investigated.

Vitamin A deficiency caused increases in the activities of kidney arginase and liver xanthine oxidase in chicks; the changes were already apparent at 11 days of age. No changes were found in the levels of alanine aminotransferase, aspartate aminotransferase, vitaminA palmitate hydrolase and vitamin A ester synthetase.

Some enzymatic activities in chicks, liver xanthine dehydrogenase (XDH), liver alanine amino transferase (GP-T, EC 2.6.1.2), liver aspartate amino transferase (GO-T, EC 2.6.1.1) and kidney arginase (EC 3.5.3.1) were studied in chicks fed 2 types of protein, soybean or gluten at 4 levels 10, 20, 30 and 40% in the diet.The determinations were conducted on 10 and 17-day-old chicks. The increase of the enzymatic activity as a function of the protein level in the diet gives a typical curve for the tested protein. The better comparison was obtained while the curves for the liver XDH were compared on 10-day-old chicks.

SUMMARYIn two feeding experiments the effects of different sources of protein on nitrogen utilization were studied. Three protein sources were examined in both experiments; (a) soya-bean oil meal; (b) lucerne hay or vetch oat hay, and (c) a mixture of soyabean oil meal and hay. The first experiment was carried out with nine adult rams and the second with twelve growing rams.The results of N balance experiments showed clearly the superiority of the hay ration over the soya-bean meal ration. N retention when the mixed ration was given was greater than on hay alone. No parallel trend was found between the protein digestibility of any of the diets and its efficiency for N retention.With adult sheep a negative correlation between the extent of N retention and blood urea concentration was found; this agreed with our earlier findings. No such negative correlation was found with growing animals.The highest concentrations of the various forms of soluble N compounds such as soluble a-amino N, diffusible N and diffusible peptide N were found in the rumen liquor taken from the sheep kept on the hay diet. The lowest amounts were observed when the soya-bean oil meal diet was given and intermediate amounts with the mixed diet. These trend sappeared to be related to the NPN (non-protein nitrogen) content of the diet, but the amounts of soluble N compounds present in rumen liquor were not directly correlated with the extent of N retention.Concentrations of VFA present in rumen liquor depended primarily on the carbohydrate composition in the diet. The type of protein ingested exerted some influence, particularly on the concentrations of caproic and iso-caproic acid. The ratios of concentrations of the individual fatty acids in blood to the concentrations of the same acids in rumen liquor were found to increase with lengthening of the fatty acid chain.

1. One feeding experiment was carried out with seven adult rams (49–65 kg) and a second with eight young rams (39–51 kg) to compare the influence of starch supplementation on the utilization of protein; soya-bean meal was the main protein source in all diets. Cottonseed hulls and Rhodes hay served as energy sources in the basal diets. The energy content of the experimental groups (four adult or four young rams) was increased to 150% of that of the control groups by addition of crushed maize while the intake of digestible protein was equalized by adding maize gluten to control diets. 2. Adult rams retained 20% more nitrogen and young rams 20% less nitrogen on the highenergy than on the control diet. The effect in young rams was not significant. 3. Addition of maize to the diets was followed by a decrease in protein digestibility, but no parallel trend was found between protein digestibility and efficiency of nitrogen retention. 4. In both experiments rumen ammonia and blood urea values were higher in sheep given the control diet than in those receiving the diet supplemented with maize. 5. The dehydrogenase activity of rumen contents from young rams was only slightly raised by the maize supplement compared with the much larger increase that occurred in adult rams. 6. The concentrations of total volatile fatty acids in the rumen contents of adult and young rams were not markedly influenced by the addition of maize to their diets but a slight increase in the concentrations of propionic and butyric acids and a decrease of the ratio of acetic to propionic acid occurred.

Enzymatic activities involved in protein metabolism — liver xanthine dehydrogenase, liver xanthine oxidase (EC 1.2.3.2), liver aspartate aminotransferase (EC 2.6.1.2), liver and kidney arginase (EC 3.5.3.1) - were studied in chicks and rats fed diets containing the following soybean meals as protein sources: 1) heated soybean meal (HSBM); 2) raw soybean meal (RSBM); 3) HSBM + RSBM (2:1); and 4) HSBM supplemented with soybean trypsin inhibitors. RSBM decreased significantly the xanthine dehydrogenase, xanthine oxidase and arginase activity as compared with HSBM, whereas aspartate aminotransferase and alanine aminotransferase were affected slightly. The HSBM + RSBM or HSBM + soybean trypsin inhibitors did not show any clear influence on enzymatic activities. Diets with 25% protein gave higher enzymatic activity than those of 15% and methionine supplementation had no significant effect. Good correlation was found between the means of xanthine dehydrogenase and arginase activities in chicks and between the means of these activities and growth rate of each group.

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