PREDICTION OF THE DIGESTIBILITY OF THE DIET OF HORSES - EVALUATION OFFECAL INDEXES

Data from in vivo digestibility trials with four to six horses fed twe nty-seven forage-based diets are used to calculate prediction equation s for the digestibility of dry and organic matter, based on the crude ash (CA), crude protein (CP) and crude fibre (CF) contents of diets an d faeces. The most precise prediction of dry matter digestibility (r.s .d. = 0.032, R-2 = 0.80) was derived from a multiple regression includ ing faecal (CP, CF) and dietary parameters (CF). Among faecal paramete rs, CP was the best single predictor of both digestibility (r.s.d. = 0 .040, r(2) = 0.63) and dietary CP content (r.s.d. = 0.028, r(2) = 0.59 ). For biological reasons we propose a non-linear model that allows pr ediction of dry- and organic-matter digestibility from faecal CP conte nt with reasonable precision (r.s.d. = 0.038, 0.036, r(2) = 0.65, 0.74 , respectively). This will be adequate for many studies, especially fo r free-living animals in rangelands.