AbstractA series of 4 × 4 Latin-square digestibility trials was carried out to determine whether there were any differences between different types of equid in their ability to digest diets containing different levels of fibre and protein. The equids (Thoroughbreds, Highland ponies, Shetland ponies and donkeys) were offered one of four molassed diets in turn and these contained different proportions of alfalfa and oat straw: 1·0:0, 0·67:0·33, 0·33:0·67, 0:1, respectively. The apparent digestibility of dry matter (DM), organic matter (OM), gross energy (GE), crude protein (CP), acid-detergent fibre (ADF) and neutral-detergent fibre (NDF) were estimated. The rate of passage of the different diets was measured using Cr-mordanted fibre (Cr-fibre) and Co-ethylene diamine tetra acetic acid.All animals digested the components of the high-fibre diets less well than those of the low-fibre diets (P < 0·001 for DM, OM, GE, CP and ADF). Donkeys digested fibre more effectively than the other equids (F < 0·01 for ADF and NDF). The gastro-intestinal transit time of the high fibre diets was significantly less than that for the low fibre diets (P < 0·001) and donkeys retained food residues longer than the other equids (P < 0·01).