Associative effects on total tract digestibility in horses fed different ratios of grass hay and whole oats

The present experiment was performed according to a 4 x 4 Latin square desi gn with diets composed of ton dry matter (DM) basis) the following ratios o f grass hay to whole oats: 100:0 (O0), 80:20 (O20), 60:40 (O40) and 40:60 ( O60). Four mature Standardbred geldings weighing 493 (S.D. 34) kg were used . The digestibility of DM, organic matter and energy (dE) increased in a cu rvilinear pattern with the increasing inclusion levels of oats. It is sugge sted that this was a reflection of the significantly lowered digestibility of nutrients and particularly of fibrous components for the O60 diet as com pared with the other three rations, thus resulting in negative associative effects between grass hay and oats. On the basis of the present data, and e xcluding the results of the O60 diet, the digestibility of dE of oats was e stimated to be 75%. As an expression of the associative effect at the O60 l evel, the dE of the total diet was estimated to be 58%, as compared with 63 % when estimated on the oats value of 75% and the O0 diet, resulting in a d epression of dE of the total diet by 8%, mainly affecting the utilization o f fibrous components. Urinary energy losses decreased with increasing level of oats. (C) 2000 Elsevier Science B.V. All rights reserved.