title: The apparent digestibility of phytate phosphorus and the influence of supplemental phytase in horses.
abstract: Availability of phytate-bound P as influenced by supplemental phytase was studied in eight horses consuming four diets in a 4 x 4 Latin square design experiment. The treatments were a control (containing a low P level, 18.4 g/d) and three high-P diets. These diets contained P as monocalcium phosphate (MCP; 43.7 g/d), myoinositol hexakisphosphate in the form of wheat and rice bran (MIHP; 41.8 g/d), or MIHP with microbial phytase (MIHPP; 42.5 g/d). The proportions of phytate-bound P were 3, 1, 55, and 56% for the control, MCP, MIHP, and MIHPP, respectively. The MIHPP diet was supplemented with 300 phytase units (FTU)/kg (as-fed basis). Feces and urine were collected quantitatively and analyzed for P, Ca, and Mg. Urinary P excretion was lower (P < 0.05) with the control diet (0 g of P/d) than with the MCP diet (1.0 g of P/d). The low urinary P excretion (0.3 g of P/d) for the MIHP diet suggested low P availability compared with the MCP diet, but apparent digestibility of P expressed as a percentage of intake did not differ (P = 0.065) between these diets. Apparent Ca digestibility was lower (P < 0.05) for the MIHP diet than for the MCP diet (26.4 vs. 42.4%). This difference may have been caused by the origin of the Ca in these diets. Phytase supplementation increased apparent Ca digestibility from 26.4 to 31.5% (P < 0.05). Magnesium was not influenced by the level of phytate in the diet. Our data indicate that phytase supplementation had more influence on Ca digestibility than on P digestibility and suggest that phytase supplementation may be beneficial for improving Ca digestibility for horses receiving a phytate-rich diet.
authors.affiliation: Department of Nutrition, Faculty of Veterinary Medicine, Utrecht University, 3584 CM Utrecht, The Netherlands.
authors.forename: D A
authors.initials: DA
authors.lastname: van Doorn
authors.forename: H
authors.initials: H
authors.lastname: Everts
authors.forename: H
authors.initials: H
authors.lastname: Wouterse
authors.forename: A C
authors.initials: AC
authors.lastname: Beynen
mesh_terms: D010832:6-Phytase / Q000494:pharmacology*; D000821:Animal Feed; D000818:Animals; D001682:Biological Availability; D002136:Calcium, Dietary / Q000493:pharmacokinetics / Q000652:urine; D019587:Dietary Supplements; D004063:Digestion; D004305:Dose-Response Relationship, Drug; D005243:Feces / Q000737:chemistry; D006736:Horses / Q000378:metabolism*; D008274:Magnesium / Q000493:pharmacokinetics / Q000652:urine; D008297:Male; D010758:Phosphorus / Q000493:pharmacokinetics* / Q000652:urine; D010833:Phytic Acid / Q000737:chemistry*; D011897:Random Allocation; D016482:Urinalysis / Q000662:veterinary
chemical_list: D002136:Calcium, Dietary; D010758:Phosphorus; D010833:Phytic Acid; D010832:6-Phytase; D008274:Magnesium