Apparent digestibility of soybean and sunflower meals in horses: comparison of evaluation systems

The objectives of this work were to determine the apparent digestibility of soybean meal and partially de-hulled sunflower meal in horses fed first-cut meadow hay- based diet, and to find the most reliable method to determine the apparent digestibility of diets by comparing the acid insoluble ash (AIA) marker method with the total feces collection method. Six saddle horses aged between 4 and 12 years, with an average trial weight of 542.0±71.8, 555.8±74.6, and 556.1±74.3 Kg, were used to determine the apparent digestibility of the rations by means of three in vivo digestibility trials. Diets were based on hay alone (100:0), hay plus soybean meal (80:20) and hay plus partially de-hulled sunflower meal (80:20) in the 1st, 2nd and 3rd trial, respectively. Feces were collected over a 6-day collection period following a 14-day adaptation period. Diet digestibility coefficients were determined for dry matter, organic matter, crude protein and gross energy, whereas the same digestibility coefficients were calculated for soybean meal and partially de-hulled sunflower meal. The results showed that the addition of soybean meal and partially de-hulled sunflower meal to first-cut meadow hay improves ration digestibility. In particular, soybean meal was found to be more digestible than partially de-hulled sunflower meal in horses. The apparent digestibility values obtained by the two methods were similar and appeared equally suitable for digestibility trials in horses.