The apparent digestibility of fibre in trotters when dietary soybean oil is substituted for an iso‐energetic amount of glucose

An attempt was made to quantify the effect of extra fat intake on fibre utilization in horses. In a 4×4 cross‐over trial with feeding periods of 24 days each, eight mature trotting horses (age 4 to 12 years, 407 to 531 kg BW) were given four diets. The concentrates were formulated to contain either soybean oil or an iso‐energetic amount of glucose or combinations of the two ingredients. The concentrates were fed in combination with the same amount of hay so that the whole diets contained 30, 50, 77 or 108 g EE/kg DM. Apart from the amounts of fat and glucose the four diets were identical. With an increase of 10g/kg DM of soybean oil the apparent total tract digestibility of crude fibre was reduced with 0.9 percentage units. Extra fat intake also reduced apparent protein and NFE digestibility, but raised apparent fat digestibility. Although the present results may hold specifically for the conditions of this study, it is suggested that the observed interaction between fat content of the diet and macronutrient utilization might have consequences for practical horse feeding in that calculating the energy content of high‐fat diets on the basis of feedstuff tables will lead to over‐ or underestimating the amount of energy provided by the various ingredients of the diets.