Abstract
Histidine is an essential amino acid for broiler chickens and a precursor for the dipeptides carnosine and anserine, but little information is available about its metabolism in modern, fast-growing broilers. We used untargeted metabolomics to investigate the metabolic changes caused by the use of different standardized ileal digestible His:Lys ratios in broiler diets with and without β-alanine supplementation. A total of 2204 broilers were randomly divided into 96 pens of 23 birds each. The pens were divided into 16 blocks, each containing one pen for all six feeding groups (total of 16 pens per group). These feeding groups were fed three different His:Lys ratios (0.44, 0.54, and 0.64, respectively) without and with a combination of 0.5% β-alanine supplementation. Five randomly selected chickens of one single randomly selected pen per feeding group were slaughtered on day 35 or 54, blood was collected from the neck vessel, and plasma was used for untargeted metabolomic analysis. Here we show that up to 56.0% of all metabolites analyzed were altered by age, whereas only 1.8% of metabolites were affected by the His:Lys ratio in the diet, and 1.5% by β-alanine supplementation. Two-factor analysis and metabolic pathway analysis showed no interaction between the His:Lys ratio and β-alanine supplementation. The effect of the His:Lys ratio in the diet was limited to histidine metabolism with a greater change in formiminoglutamate concentration. Supplementation of β-alanine showed changes in metabolites of several metabolic pathways; increased concentrations of 3-aminoisobutyrate showed the only direct relationship to β-alanine metabolism. The supplementation of β-alanine indicated few effects on histidine metabolism. These results suggest that the supplements used had limited effects or interactions on both His and β-alanine metabolism. In contrast, the birds' age has the strongest influence on the metabolome.