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.

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Soaking can affect respirable dust particles and the concentrations of some nutrients in alfalfa and cool season grass hays. However, the effect of soaking on nitrates in hay has not been reported. The aim of this study was to evaluate the effects of soaking on teff hay, a warm season annual grass, that contained high concentrations of nitrate (>2.0%). Six bales of teff hay were used for the study. Six 0.5 kg samples were taken from each bale and assigned to 1 of 6 soaking treatments; no soaking (control), cold water immersion for 10 s, warm water immersion for 10 s, cold water soaking for 1 h, warm water soaking for 1 h, and cold water soaking for 8 h. After soaking, hay was dried, ground and submitted to a commercial laboratory for analysis. Data were analyzed by analysis of variance as a block design. When the main effect of treatment was significant (P < 0.05) means were separated by Tukey's honest significant difference test. Soaking for 1 or 8 h decreased WSC (P < 0.0001). Phosphorus, potassium, sodium, and zinc concentrations were reduced by soaking for 1 h or longer (P, K, Na: P < 0.0001; Zn: P = 0.003). Nitrate concentrations were reduced (P < 0.0001) to safe levels for horses (≤ 0.5%) by soaking hay for 1 h or longer but soaking also reduced the concentrations of some nutrients in the hay. Minimal differences were observed between cold and warm soaking temperatures.

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