Feeding ground and pelleted hay rather than chopped hay to ponies: 1. Consequences for in vivo digestibility and rate of passage of digesta

This study was designed to evaluate the effect of the physical form of a hay diet on total tract digestibility in ponies, with particular emphasis in fibre digestion and digesta passage rate. Ten gelded ponies (four of them fitted with cannulae in the cecum and the right-ventral colon) were kept on wood shavings and fed twice daily a maintenance diet of equal parts Lucerne and Cocksfoot hay. The hay was either chopped (CH) or ground (1.5 mm screen) and pelleted (GPH). The apparent total tract digestibility of dry matter (DM), organic matter (OM), and fibre fractions was measured in the six non-fistulated ponies using a crossover design. Two trials were conducted to measure mean retention time (MRT) of digesta in the whole digestive tract in four non-fistulated and four fistulated animals using rare earth labelled hay and Cr-EDTA as markers of the particles and solutes, respectively. In a third trial, MRTs in the hind gut and the colon, as well as in the entire tract, were determined in the fistulated ponies using various markers given by mouth and through the cannulae. OM and fibre digestibility were not significantly different (P>0.05) between diets. However, particle (P<0.05) and solute (P<0.001) MRT were significantly longer on GPH compared to CH as a consequence of an increased retention in the colon. The longer MRTs with GPH did not significantly affect fibre digestibility. This implies a reduction in the rate of fibre degradation in the hindgut in the GPH fed animals.