The influence of exogenous phytase on the post-enteral availability of amino acids in broiler chickens offered wheat-based diets

Abstract

To investigate the influence of exogenous phytase inclusions in poultry diets on the post-enteral availability of amino acids, wheat-soybean meal diets containing 0, 500, 1000 and 2000 phytase units (FTU)/kg were offered to eight replicate cages (six birds per cage) or a total of 192 male Ross 308 chicks from 7 to 28 days post-hatch. The parameters determined included growth performance, nutrient utilisation, bone mineralization, parameters of gizzard functionality, apparent ileal digestibility coefficients and disappearance rates (g/bird/day) of amino acids, plus concentrations of amino acids, glucose and ammonia in plasma from the portal circulation (anterior mesenteric vein). The inclusion of 500 FTU/kg significantly improved weight gain by 8.39% (1485 versus 1370 g/bird) and feed conversion ratio (FCR) by 5.10% (1.397 versus 1.472 g/g) in comparison to the control. Phytase inclusions significantly increased gizzard pH but not toe ash. The 2000 FTU/kg phytase inclusion significantly increased digestibility of 15 from 16 amino acids by an average of 5.29% (0.716 versus 0.680) and significantly increased apparent metabolisable energy (AME) by 0.45 MJ (12.43 versus 12.88 MJ) and N-corrected AME (AMEn) by 0.45 MJ (11.43 versus 11.88 MJ) relative to the control. The 500 FTU/kg phytase inclusion significantly increased free concentrations of seven amino acids (isoleucine, leucine, lysine, phenylalanine, tryptophan, valine and serine) in plasma from the anterior mesenteric vein based on pairwise comparisons and numerically increased concentrations of a further six amino acids. Phytase inclusions linearly reduced concentrations of glutamic acid and glutamine in the portal circulation, and there was a logarithmic relationship between phytase inclusions and increased plasma glucose concentrations. Reductions in the ratio of glutamate plus glutamine to glucose concentrations in portal plasma were significantly related to improvements in FCR. The outcomes of this study indicate that phytase can positively influence the post-enteral availability of amino acids. The inference is that phytase is manipulating the metabolic fates of amino acids and glucose in the gut mucosa and consideration is given to the possible responsible mechanisms for the observed outcomes.