Any method to increase the utilisation of nutrients from feeds given to horses exercised on a regular basis is important. Commercially-available dried yeast cultures, used as supplements to equine diets have been shown to increase the digestibility of gross energy and enhance the retention of N in yearling horses (Glade and Biesik, 1986). There is however, limited information on whether the increase in digestibility of GE or enhancement in retention of N occurs in mature horses (Glade and Campbell-Taylor, 1990). The aim of the research reported here was to determine the effect of a dried live yeast culture on the digestibility of nutrients from a mixed diet given to riding school horses.

Six 2 and 3 year old riding school horses (mean live-weight 433 (s.e. 11.1) kg) were allocated to three balanced 2 x 2 Latin squares with two treatments and two periods of 3 weeks. The first 14 days of each period was a preliminary and the last 7 days was for measurement. The horses were housed individually (bedded on saw dust) and given 13.5 kg DM hay and 3.0 kg DM concentrate mix as a base diet. The base diet was either supplemented with 10 g dried yeast culture (S) or not supplemented (N).