Supplemental microbial phytase improves zinc utilization in broilers.
Day-old male broilers (n = 384) were used in a 21-d trial to investigate the effect of microbial phytase on the retention and utilization of Zn. A corn-soybean isolate basal diet containing 20 ppm Zn was fed alone and supplemented with 5, 10, or 20 ppm Zn as ZnSO4.7H2O or with 150, 300, 450, or 600 U of phytase/kg of diet. Total excreta were collected during Days 18 to 20. Toe, tibia, and liver samples were taken at the end of the experiment. Adding Zn and phytase to the low Zn basal diet linearly increased BW gain and feed intake of broilers (P < 0.01). The gain to feed ratio was not changed by adding Zn but was decreased by adding phytase (P < 0.01). The amount of DM retained was linearly increased by adding Zn and phytase (P < 0.10), but DM retained as a percentage of intake was only increased by adding Zn (P < 0.05). The amount of Zn retained per bird was linearly improved by adding Zn and phytase (P < 0.01). Zinc retained as a percentage of intake was linearly decreased by adding Zn but was linearly increased by adding phytase (P < 0.10). Ash percentage of toe and tibia were not affected by adding Zn but were linearly improved by adding phytase (P < 0.10); however, the amount of ash in toe or tibia was increased by Zn (P < 0.05) and phytase (P < 0.01 for toe; not significant for tibia). The concentration and amount of Zn in toe and tibia were linearly increased by adding Zn and phytase (P < 0.001). The concentration of Zn in liver increased by adding Zn (P < 0.10) but was not significantly improved by adding phytase. The amount of Zn retained in liver was linearly improved by adding Zn and phytase (P < 0.05). Nonlinear or linear response equations of the effects of Zn and phytase levels were generated and used to calculate the Zn equivalency values. The average function of Zn equivalency values (Y, milligrams per kilogram) of microbial phytase (X, units per kilogram of diet) was developed: Y = 0.20 + 0.0082X. The results indicate that approximately 0.9 mg of Zn was released per 100 U of phytase over the range of 150 to 600 U of phytase.
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Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061-0306, USA.
Kornegay
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Denbow
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DM
D010832:6-Phytase / Q000494:pharmacology*; D000821:Animal Feed; D000818:Animals; D002645:Chickens / Q000254:growth & development / Q000378:metabolism*; D004032:Diet / Q000592:standards / Q000662:veterinary; D004305:Dose-Response Relationship, Drug; D005527:Food, Fortified; D016014:Linear Models; D008099:Liver / Q000737:chemistry; D008297:Male; D011897:Random Allocation; D013025:Glycine max / Q000592:standards; D013977:Tibia / Q000737:chemistry; D014033:Toe Joint / Q000737:chemistry; D003313:Zea mays / Q000592:standards; D015032:Zinc / Q000008:administration & dosage / Q000032:analysis / Q000493:pharmacokinetics*
D010832:6-Phytase; D015032:Zinc