Improving phosphorus availability in soybean meal for broilers by supplemental phytase.
A 21-d experiment was conducted with day-old male broilers (n=840) to evaluate the effectiveness of supplemental phytase for improving the availability of phytate P in soybean meal when varying levels of P were fed. The semi-purified basal diet (.18% phytate P) contained soybean meal as the only protein source. Seven levels of phytase (0, 200, 400, 600, 800, 1,000, and 1,200 U/kg diet) were added to diets formulated to contain .20, .27, or .34% nonphytate P (nP; or .38, .45, and .52% total P, respectively). The desired levels of nP in the three basal P diets were achieved by adding varying amounts of defluorinated phosphate. A 2:1 Ca:total P ratio was maintained in all diets. Body weight gains and feed intake were improved (P < .001) by phytase at all nP levels, but the magnitude of response was greatest at low nP levels, resulting in an nP by phytase interaction (P < .01). Gain:feed was unaffected by phytase addition. A high mortality (35 to 45%) was observed for the .20 and .27% nP diets without added phytase, but this declined to normal levels with the addition of 200 to 400 U phytase/kg diet. Ash percentage of toes and tibia and shear force and stress of tibia increased with added phytase. These responses clearly show that the phytate-bound P in soybean meal was made more available to broilers by microbial phytase, and the total response was related to the phytase and nP/total P levels. Based on the high R2 values for the second order translog equations, BW gain, feed intake, and toe ash percentage were the most sensitive indicators to assess P availability, followed by tibia force and ash percentage. Derived nonlinear and linear equations for BW gain and toe ash percentage at the two lower nP levels were used to calculate P equivalency values of phytase for inorganic P. Using the average function of P released ( gamma ) by microbial phytase ( chi ) derived with nP levels of .20 and .27% for BW gain and toe ash percentage, gamma = 1.120 - 1.102e-.0027chi, 1 g of P could be released with 821 U of phytase. The amount of P released increased with increasing levels of phytase, but the amount of P released per 100 U of phytase decreased. Released P ranged from 31 to 58% of phytate P for 250 to 1,000 U of phytase/kg of diet.
Denbow
D M
DM
Department of Animal and Poultry Sciences, Virginia Polytechnic Institute, Blacksburg 24061-0306, USA.
Ravindran
V
V
Kornegay
E T
ET
Yi
Z
Z
Hulet
R M
RM
D010832:6-Phytase / Q000008:administration & dosage*; D000821:Animal Feed; D000818:Animals; D001682:Biological Availability; D015519:Bone Density / Q000187:drug effects; D002645:Chickens / Q000378:metabolism*; D004435:Eating / Q000187:drug effects; D005527:Food, Fortified; D008297:Male; D016226:Phosphorus, Dietary / Q000008:administration & dosage / Q000493:pharmacokinetics*; D013025:Glycine max; D013977:Tibia / Q000502:physiology; D014034:Toes / Q000502:physiology; D015430:Weight Gain / Q000187:drug effects; D016474:Weight-Bearing / Q000502:physiology
D016226:Phosphorus, Dietary; D010832:6-Phytase