Exposure to high ambient temperature is detrimental to the poultry industry. To understand the influence from a metabolic perspective, we investigated the effects of exposure to high ambient temperature on plasma low-molecular-weight metabolite levels in chicks using gas chromatography/mass spectrometry-based non-targeted metabolomic analysis. Heat exposure for 4 days suppressed growth and food intake. Of the 92 metabolites identified, the levels of 29 decreased, whereas the levels of nine increased. We performed an enrichment analysis on the identified metabolites and found 35 candidates for metabolic processes affected by heat exposure. Among them, the sulfur amino acid metabolic pathway was clearly detected and the levels of the following related metabolites were decreased: cystathionine, cysteine, cystine, homocysteine and hypotaurine. Changes in the kynurenine pathway in tryptophan metabolism, which is linked to the immune system and oxidative stress, were also observed: kynurenine and quinolinic acid levels increased, whereas nicotinamide levels decreased. These results suggest the possible involvement of various metabolic processes in heat-exposed chicks. Some of these metabolites would be important to understand the mechanism of biological responses to high ambient temperature in chicks.

The effect of various branched-chain amino acids (BCAA : isoleucine, leucine, valine) on embryo growth and the hatching time of fertilized eggs of chickens was examined. Before the onset of egg incubation, one of BCAA was injected into fertilized eggs. The amount of each BCAA administrated into eggs was equal to 1% of each amino acid exits in the egg. On day 14 of incubation, the weight of embryos was measured. On day 21, the hatching time was recorded, and body weight of chicks at birth was measured. The in ovo administration of BCAA increased the weight of whole embryo compared to the control. Compared to the control, the in ovo administration of leucine and valine significantly accelerated the hatching time. There were no significant differences in body weight of newly hatched chicks among all treatments. It was concluded that the in ovo administration of BCAA, especially leucine and valine, could accelerate embryo growth resulting in the acceleration of hatching time of chicks.

Glucagon-like peptide-1 (GLP-1) is secreted by L cells in the small intestine in response to food ingestion. The influence of supplementation to diet with the amino acids, methionine (Met) and lysine (Lys), on the L cells in chicken small intestine was investigated using immunohistochemical and morphometrical techniques. Many endocrine cells showing immunoreactivity for GLP-1 antiserum were observed in the control, crude protein (CP) 0%, CP 0%＋Met and CP 0%＋Lys groups. The GLP-1-immunoreactive cells in all the groups were "open-typed" endocrine cells as viewed under light and electron microscopes. Differences in the shape and distributional pattern of GLP-1-immunoreactive cells were not observed between the control and experimental groups. Frequencies of the occurrence of GLP-1-immunoreactive cells in the CP 0%＋Met and CP 0%＋Lys groups were significantly lower than that of the CP 0% group, but significant differences were not recognized between the control group and the CP 0%＋Met and CP 0%＋Lys groups. Secretory granules in the control group were round to oval in shape. Elongated secretory granules were observed in the experimental groups, but not in the control group. Ratios of GLP-1-immunoreactive cells with elongated secretory granules in the CP 0%＋Met and CP 0%＋Lys groups were decreased compared with that in the CP 0% group. The size of round secretory granules in the control group was larger than that in all the groups. However, sizes of round secretory granules in the CP 0%＋Met and CP 0%＋Lys groups were larger than that in the CP 0% group. These morphological results indicate that amino acids may be a signal that influences on the secretion of GLP-1 in chicken small intestine.

When tryptophan is glycated with glucose, it results in forming two types of glycated tryptophan compounds, glucose-tryptophan Amadori product and (1R, 3S) -1-(D-gluco-1, 2, 3, 4, 5-pentahydroxypentyl) -1, 2, 3, 4-tetrahydro-β-carboline-3-carboxylic acid (PHP-THβC). As hyperglycemia and high body temperature are the characteristics in avian species, these are supposed to elevate the concentration of glycated tryptophan compounds in the plasma of chickens. However, there was no attempt to detect two types of glycated tryptophan compounds in the plasma of chickens, so far. Therefore, young chickens were fed tryptophan-excess diets (0, 1, 2 or 3% excess) for 14 days, and glycated tryptophan compounds were detected using a liquid chromatograph mass spectrometer (LC/MS). In the present study, two types of glycated tryptophan compounds, glucose-tryptophan Amadori product and PHP-THβC, were successfully detected in the plasma of chickens, and plasma levels of both glycated tryptophan compounds significantly correlated to plasma tryptophan concentration.

When tryptophan is glycated with glucose, it results in forming two types of glycated tryptophan, glucosetryptophan Amadori product and (1R, 3S)-1-(D-gluco-1,2,3,4,5-pentahydroxypentyl)-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (PHP-THβC). Hyperglycemia and high body temperature in avian species are supposed to elevate the concentration of glycated tryptophan in the plasma of chickens fed tryptophan-excess diets. However, plasma concentrations of both glucose-tryptophan Amadori product and PHP-THβC have not been determined so far. Young chickens were fed tryptophan-excess diets (1, 2 or 3% excess) for 14 or 21 days, and plasma concentrations of two types of glycated tryptophan were measured using liquid chromatograph mass spectrometer (LC/MS). In the present study, we successfully detected and quantified both glucose-tryptophan Amadori product and PHP-THβC in the plasma, which revealed that plasma concentrations of glucose-tryptophan Amadori product and PHP-THβC were approximately 1 and 2-4 μM, respectively. Furthermore, plasma concentrations of glycated tryptophan compounds significantly correlated to that of plasma tryptophans, and total amount of both glycated tryptophan compounds was almost 10% of plasma tryptophan.