The effects of supplementary bacterial phytase on dietary energy and total tract amino acid digestibility when fed to young chickens
Résumé
Abstract 1. Four diets were offered to broiler chickens from 7 to 17 days of age; these included a phosphorus-adequate positive control (PC) (4.7 g/kg available P), a sub-optimal P negative control (NC, 2.5 g/kg available P) with (500 and 12500 FTU/kg) and without phytase. Dietary apparent metabolisable energy (AME), dietary net energy for production (NEp), the efficiency of AME retention (Kre), heat production and total tract amino acid digestibility coefficients were determined. The determination of NEp involved a comparative slaughter technique in which growing chickens were fed the experimental diets ad libitum. 2. Feed intake, weight gain and feed conversion efficiency increased (P<0.05) in a dose dependent manner in response to dietary phytase activity. Overall, the NEp of the phytase supplemented diets improved (P<0.001) by approximately 15.6% compared to the negative control while dietary AME was not affected. Although phytase did not affect AME the large increase in the NEp demonstrates that dietary phytases improved energy utilization, i.e. diverting more energy for production, which is not accounted for in the AME procedure. This is largely a result of the stimulatory effect that phytase has on feed intake rather than on digestibility of the diet. 3. Overall, the diet supplemented with 12500 FTU had 6.4 % improvement (P<0.05) in total tract digestibility coefficients of the total amino acids compared to the negative control. With regards to individual amino acids, the impact of phytase was far more pronounced for threonine, an important component of the gastrointestinal mucin, compared with others. 4. Dietary NEp was more highly correlated with performance criteria than dietary AME and seems to be more sensitive way to evaluate broiler response to phytase supplementation.
Domaines
Biologie animale
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