THE EFFECT OF LEVEL OF FEED-INTAKE ON NUTRIENT AND ENERGY DIGESTIBILITIES AND RATE OF FEED PASSAGE IN HORSES

The effect of feeding maintenance (M) and 1.4 x M levels of intake of alfalfa cubes on digestibilities and rate of passage was determined in six mature gelding horses. In addition, the efficacy of using chromic oxide as a digestibility marker and dysprosium (Dy) as a passage rate marker, when fed as part of supplemental vitamin-mineral pellets, was evaluated. Digestibility coefficients for dry matter, crude protein a nd gross energy were not different (p > 0.05) at either level of intak e. Moreover, all digestibility coefficients determined from chromic-ox ide recovery were similar (p, 0.05) to values obtained by the total-co llection method. Dry matter digestibilities for faecal grab samples ta ken at 0800 h were 7.4 and 6.1 percentage units higher (p < 0.05) comp ared with samples taken at 2000 h when determined by the recoveries of Dy and chromic oxide, respectively. There was no difference (p > 0.05 ) between maintenance and 1.4 x M horses for transit time and mean ret ention time (MRT) of digesta when determined by simple regression anal ysis based on the decline in concentration of Dy versus time after the marker was withdrawn from the diet. Alternatively, when MRT were dete rmined mathematically by two methods using marker concentrations at di fferent time intervals, maintenance MRT was greater (p < 0.05) at 24.6 and 25.8 h compared with 15.3 and 15.9 h at 1.4 x M level of intake. In conclusion, chromic oxide is suitable as a digestibility marker, wh ereas, Dy is useful as a marker to study relative rates of passage in horses.