title: Effects of phytase supplementation on phosphorus retention in broilers and layers: a meta-analysis.
abstract: Phytase, a widely used feed additive in poultry diets, increases P availability and subsequently reduces inorganic-P supplementation and P-excretion. Phytase supplementation effect on P-retention in poultry has been investigated, but the effect sizes were highly variable. The present study's objective was to conduct several meta-analyses to quantitatively summarize the phytase effect on P-retention in broilers and layers. Data from 103 and 26 controlled experiments testing the phytase effect on P-retention were included in 2 separate meta-analyses for broilers and layers, respectively. The mean difference calculated by subtracting the means of P-retention for the control group from the phytase-supplemented group was chosen as an effect size estimate. Between-study variability (heterogeneity) of mean difference was estimated using random-effect models and had a significant effect (P < 0.01) in both broilers and layers. Therefore, random-effect models were extended to mixed-effect models to explain heterogeneity and obtain final phytase effect size estimates. Available dietary and bird variables were included as fixed effects in the mixed-effect models. The final broiler mixed-effect model included phytase dose and Ca-to-total-P ratio (Ca:tP), explaining 15.6% of the heterogeneity. Other variables such as breed might further explain between-study variance. Broilers consuming control diets were associated with 48.4% P-retention. Exogenous phytase supplementation at 1,039 FTU/kg of diet increased P-retention by 8.6 percentage units on average. A unit increase of phytase dose and Ca:tP from their means further increased P-retention. For layers, the final mixed-effect models included dietary Ca, age, and experimental period length. The variables explained 65.9% of the heterogeneity. Layers receiving exogenous phytase at 371 FTU/kg were associated with a 5.02 percentage unit increase in P-retention. A unit increase in dietary Ca from its mean increased P-retention, whereas an increase in the experiment length and layer's age decreased P-retention. Phytase supplementation had a significant positive effect on P-retention in both broilers and layers, but effect sizes across studies were significantly heterogeneous due to differences in Ca contents, experiment length, bird age, and phytase dose.
authors.affiliation: Animal Nutrition Group, Wageningen University, Wageningen, PO Box 338, 6700 AH, the Netherlands Department of Animal Science, University of California, Davis 95616 ad.bougouin@gmail.com.
authors.forename: A
authors.initials: A
authors.lastname: Bougouin
authors.affiliation: Department of Animal Science, University of California, Davis 95616.
authors.forename: J A D R N
authors.initials: JA
authors.lastname: Appuhamy
authors.affiliation: Department of Animal Science, University of California, Davis 95616.
authors.forename: E
authors.initials: E
authors.lastname: Kebreab
authors.affiliation: Animal Nutrition Group, Wageningen University, Wageningen, PO Box 338, 6700 AH, the Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Dijkstra
authors.affiliation: Animal Nutrition Group, Wageningen University, Wageningen, PO Box 338, 6700 AH, the Netherlands.
authors.forename: R P
authors.initials: RP
authors.lastname: Kwakkel
authors.affiliation: Centre for Nutrition Modelling, Department of Animal and Poultry Science, University of Guelph, Guelph, ON, N1G 2W1, Canada.
authors.forename: J
authors.initials: J
authors.lastname: France
mesh_terms: D010832:6-Phytase; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002136:Calcium, Dietary / Q000378:metabolism; D002645:Chickens / Q000378:metabolism*; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D008954:Models, Biological; D010758:Phosphorus / Q000378:metabolism*
chemical_list: D002136:Calcium, Dietary; D010758:Phosphorus; D010832:6-Phytase
keywords: broiler; layer; phosphorus retention; phytase