Jesse I. Morrison1, S. Ray Smith1, and Glen E. Aiken2. (1) Plant and Soil Sciences, University of Kentucky, N-222 Ag Science Center North, Lexington, KY 40546, (2) Forage-Animal Production Research Unit, USDA-ARS, Room N220 Agriculture Science Center North, Lexington, KY 40546
Microhistological analysis is a highly effective microscopic technique of determining botanical composition of animal diets by visual recognition of fecal plant fragments, and has been widely used in range studies. The objective of this study was to use microhistological techniques to predict the botanical composition of domesticated horse diets when grazing mixed cool-season pasture. Samples of tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire], bluegrass (Poa pratensis L.) and orchardgrass (Dactylis glomerata L.) were evaluated for microscopically unique characteristics. Initial experiments validated microhistological analysis as an effective technique for determining botanical composition of cool season grass fecal samples. Cool season pasture grazing studies were conducted in October, 2006 and May, 2007 in Lexington, KY. Four 0.5 acre paddocks with high amounts of tall fescue and 4 with low tall fescue were evaluated for percent botanical composition by using a 0.6 m2 (2’ x 2’) quadrat. Visual estimation, point quadrat analysis, and hand separation were used to determine botanical composition and dry matter availability. One Thoroughbred mare was placed in each individual paddock and allowed to graze freely for 6 days, and fecal samples were taken from paddocks on days 4-6. Fecal samples from day 5 were used for analysis to insure against contamination from pre-study herbage intake. Horses selectively grazed bluegrass more in the fall than in the spring. For each percent increase of tall fescue or orchardgrass in the paddock, there was a corresponding increase of 0.44% and 0.42%, respectively, in the diet. In conclusion, microhistological analysis is a useful tool for determining botanical composition of horse diets when grazing cool season grass pastures.
