Methods for investigating intestinal absorption of amino acids in chicken intestine in vitro

Certain techniques for measuring amino acid absorption are considered, their specific roles are defined and both theoretical and practical considerations are used to evaluate each system. Some methodological considerations are presented.

The effect of diet on liver glycogen and body composition in the chick

Experiments were conducted to study the effects of diet on liver glycogen and body composition in the three-week-old chick. When percent protein and percent lysine were varied, liver glycogen concentration declined significantly as protein and lysine increased, 32.6 vs. 19.4 mg/g for the 14 and 35% protein diets, respectively. Carcass fat decreased and carcass moisture increased in a pattern similar to glycogen as protein and lysine increased in the diets. When seven levels of lysine were fed in isocaloric, isonitrogenous diets, glycogen content was not significantly different in any of the treatments. Liver glycogen was highest at the lowest energy level when dietary energy was increased and protein held constant. Carcass fat varied with the energy level but was also influenced by the amino acid balance. The data suggest that percent carbohydrate to percent fat ratio in the diet (both calculated) is an important factor affecting glycogen, but more research is needed to determine the mechanisms controlling the glycogen content of the liver.

Amino acid uptake in chickens subjected to increasing levels of quantitative food restriction

1. Three groups of cockerels were reared from 3 to 11 weeks of age on increasingly severe quantitative food restriction treatments, resulting in body-weight values of 12, 19 and 27% below that of a control group which was fed ab lib. 2. The rate of uptake of L-arginine, glycine, L-lysine and L-phenylalanine was measured in vitro using intestinal rings, over a 5 min incubation period. 3. Uptake of L-arginine was significantly increased with increasing degrees of body-weight restriction. This amino acid and L-lysine were the only two to show a significantly enhanced uptake rate as a result of the restriction treatments. 4. No significant differences were noted in the case of glycine or L-phenylalanine uptake following food restriction, indicating a certain selectivity in the alteration of absorption rates following food restriction, when such tests are conducted in vitro.

Uptake of certain amino acids in vitro in chickens previously subjected to three methods of dietary restriction

From 8 weeks of age cockerels and pullets were restricted for 8 or 12 weeks either by rationing, by feeding a low lysine diet or by feeding a diet low in protein but balanced in respect of all amino acids. 2. There was a significant decrease in growth rate of the birds as a result of the restrictive treatments. 3. The dietary treatments affected the rate of uptake of the four amino acids tested--arginine, lysine, histidine and glycine--although the effect was not significant in all cases, neither was it consistent throughout.

Sodium dependence and counterflow of some amino acids in chick intestine

By incubating chicken intestinal rings in buffer containing either sodium or mannitol, it was demonstrated that uptake of L-lysine and L-histidine is sodium dependent. Double reciprocal plots of the data indicated that Vmax was independent of sodium concentration. KM values, however, were increased considerably in the absence of the metal, indicating a decreased affinity of the amino acid for a hypothetical carrier. A failure to demonstrate mobile carriers for L-lysine and L-arginine in chick intestine is reported. Counterflow results are briefly discussed in terms of fixed binding sites.

The sequential feeding of growing chickens

1. Male chickens, I week old, were fed alternately for 6 or 12 h periods with diets complementary in their amino acid composition. The isonitrogenous, isoenergetic diets were based on fish meal or sunflower meal as the sole source of protein, or fish meal-sunflower (40:60, w/w); each diet contained 120 g crude protein/kg. Other groups of chickens were given these diets ad lib. 2. Net protein utilization (NPU) values obtained after a I-week experimental period indicated that sequential feeding for bot 6 and 12 h resulted in significantly improved responses compared with chickens given the same diets ad lib. These results suggested that the two protein sources, although provided at separate times, could complement each other. 3. In certain treatments there was a 6 or 12 h fasting period between feeding periods to reduce the effect of nutrients from the previous period. 4. For alternate feeding and fasting periods of 6 h with the combined diet, food intake and gain in body-weight were both significantly reduced compared with the corresponding values for the combined diet fed ad lib. The NPU value was virtually the same for both treatments. For 12 h periods of alternate feeding and fasting the gain in body-weight was only just significantly lower than that for the control group (combined diet fed ad lib.), but the NPU value was highly significantly better than that for the control group. 5. For the treatments which included 6 and 12 h fasting periods between the two single-protein diets, the food intake and gain in body-weight were significantly lower compared with the treatment groups given alternate feeding thd fasting periods of either 6 or 12 h with the combined diet. The NPU values for the two groups given 12 h alternate feeding and fasting periods differed significantly, whereas the NPU values for the two groups given 6 h feeding and fasting periods were the same.