Phosphorus digestibility and phytate degradation by yearlings and mature horses

A. L. Fowler, T. L. Hansen, L. A. Strasinger, B. E. Harlow, L. M. Lawrence

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


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 (P = 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 (P = 0.190). Apparent Ca digestibility was lower in mature geldings (P = 0.043), but apparent Mg digestibility did not differ between ages (P = 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.

Original languageEnglish
Pages (from-to)5735-5742
Number of pages8
JournalJournal of Animal Science
Issue number12
StatePublished - Dec 18 2015

Bibliographical note

Publisher Copyright:
© 2015 American Society of Animal Science. All rights reserved.


  • Equine
  • Fecal collections
  • Mineral
  • Phosphorus
  • Phytate

ASJC Scopus subject areas

  • Food Science
  • Animal Science and Zoology
  • Genetics


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