Effects of phytase supplementation in mature horses fed alfalfa hay and pelleted concentrate diets

Abstract

An experiment was conducted to study P digestibility in mature horses because of the growing environmental concerns regarding P runoff and previous equine research focused mostly on young and growing animals or used ponies as a model. Phytase supplementation of swine and poultry diets can result in greater phytate-P digestibility, leading to a decreased need for inorganic P supplementation and a decrease in P excreted to the environment; this, however, has not been demonstrated in the horse. Six mature Arabian geldings were fed 6 diets consisting of pelleted concentrate and alfalfa hay. The concentrates consisted mainly of soybean hulls, ground corn, wheat midds, broken rice, and beet pulp, and phytase was added to the concentrates accordingly before pelleting. There were 3 diet types: control (concentrate and hay), high P (greater P concentrate and hay), and forage only, and each diet type included 1 phytase-supplemented diet and 1 non-phytase-supplemented diet, resulting in 6 total diets. Phytase supplementation for the forage only diet was accomplished by feeding a nominal amount of concentrate formulated solely as a vehicle for the phytase. Horses had unrestricted access to water throughout the experiment. Using a Latin square design, all horses received all diets over a period of 12 wk. In each week, the new diet was fed for 11 d of diet acclimation, which was followed by a 3-d total collection of feces and urine for each horse. There was no effect (P < 0.05) of phytase supplementation on P output in the urine or feces, resulting in no differences in P apparent digestibility. Analysis of the feed and feces for phytate revealed a 93% average disappearance rate of phytate, indicating that horses are highly capable of degrading phytate and that phytase supplementation was not beneficial. Thus, the results indicate that mature horses are able to maintain a near 0 P balance, with adequate P provided in the diet even as phytate, and increased P intakes above requirement may result in increased potentially detrimental outputs to the environment.

The Effect of Diet Composition on the Digestibility and Fecal Excretion of Phosphorus in Horses: A Potential Risk of P Leaching?

“…The observed digestibilities of Ca not differing between the diets agreed with the literature values [2,7,18,35]. Van Doorn et al [18] have reported that high amounts of P and phytate P may decrease Ca digestibility.…”

“…The larger excretion of Mg compared with its intake in all diets, except those including the complete feed, explains, the poor Mg digestibility in these diets. The digestibility of Mg has been reported to be largely varying, and negative values have also been reported [2,7,18,35], as in the present study. Because Ca and Mg are excreted in large quantities in urine [9,40], the observed digestibilities here may be underestimated.…”

“…Macro-mineral phosphorus plays an important role in bone formation as a constituent of phosphoproteins, phospholipids, and nucleic acids, and in energy and fat metabolism [1][2][3]. In animals, 80-85% of phosphorus is stored in the bones and teeth, and the remainder in soft tissues and body fluids [3].…”

Furosemide administration results in a transient alteration in calcium balance in mature horses

“…For calcium analysis, urine was acidified with 12 M HCl (EMD Chemicals) at a rate of 20 μl/ml of urine to ensure all precipitate was in solution (O'Connor‐Robison & Nielsen, 2006). Faecal and hay samples were oven‐dried for 24‐hr (Thelco; Precision Scientific), ground to 1 mm particles (Cyclotec 1093 Sample Mill; Foss) and microwave digested (MARS5; CEM Corp.) with nitric acid (70% trace‐metal grade; Fisher Scientific) in duplicate as described by Shaw, Rozeboom, Hill, Booren, and Link (2002) and Lavin et al (2013). Calcium concentrations in hay, faeces, and urine were determined by atomic absorption spectroscopy (AA‐7000; Shimadzu) with each urine sample and microwave digest run in duplicate.…”

Phosphorus excretion by mares post‐lactation

“…Dietary P requirements for horses are calculated using estimates of true digestibility of 35% or 45% depending on the form of P in the diet (NRC, 2007). However, in the equine literature true P digestibility values have been reported to range from −10% to 79% (Kichura, Hintz, & Schryver, 1983; Lavin et al, 2013), but there is no consensus on why this large variation occurs. In cattle, true P digestibility is 80% (NRC, 2001).…”