title: Phosphorus digestibility and phytate degradation by yearlings and mature horses.
abstract: Inorganic P is often added to growing horse diets because organic P, or phytate-P, is believed to have lower digestibility. If horses can efficiently digest organic P, then the need for inorganic P may be reduced. Much of the P in grain-based concentrates fed to growing horses is in the form of phytate-P. Little is known about the ability of growing horses to degrade phytate-P or whether horse age affects mineral digestion in horses. The objective of this study was to examine the effect of age on P, Ca, and Mg digestibility as well as phytate-P degradation. Four yearling geldings and 4 mature geldings were fed a diet of alfalfa cubes, timothy cubes, and a pelleted concentrate. The diet contained 0.28% total P and 17.4% of that P was in the phytate form. There was a 14-d diet adaptation period followed by a 4-d fecal collection period. Apparent total tract P digestibility was higher for yearlings than mature geldings ( = 0.036; 7.7 and -6.6% for yearlings and mature geldings, respectively). Phytate-P disappearance was 94.8% and did not differ between ages ( = 0.190). Apparent Ca digestibility was lower in mature geldings ( = 0.043), but apparent Mg digestibility did not differ between ages ( = 0.414). Phytate is broken down in the gastrointestinal tract, but the low P digestibilities suggest that either degradation occurs after the site of P absorption or liberated P is recycled back into the gastrointestinal tract. Yearlings can utilize organic P as well as mature horses; therefore, diets without inorganic P are acceptable for growing horses.
authors.forename: A L
authors.initials: AL
authors.lastname: Fowler
authors.forename: T L
authors.initials: TL
authors.lastname: Hansen
authors.forename: L A
authors.initials: LA
authors.lastname: Strasinger
authors.forename: B E
authors.initials: BE
authors.lastname: Harlow
authors.forename: L M
authors.initials: LM
authors.lastname: Lawrence
mesh_terms: D000375:Aging / Q000502:physiology*; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002136:Calcium, Dietary / Q000008:administration & dosage / Q000378:metabolism; D004032:Diet / Q000662:veterinary; D004063:Digestion; D002523:Edible Grain / Q000378:metabolism; D005243:Feces / Q000737:chemistry; D041981:Gastrointestinal Tract / Q000378:metabolism; D006736:Horses / Q000378:metabolism / Q000502:physiology*; D008274:Magnesium / Q000008:administration & dosage / Q000378:metabolism; D008297:Male; D000455:Medicago sativa / Q000378:metabolism; D016226:Phosphorus, Dietary / Q000008:administration & dosage / Q000378:metabolism*; D010833:Phytic Acid / Q000378:metabolism*
chemical_list: D002136:Calcium, Dietary; D016226:Phosphorus, Dietary; D010833:Phytic Acid; D008274:Magnesium