EFFECTS OF MACERATION AT MOWING ON DIGESTIBILITY AND RUMINAL FERMENTATION OF TIMOTHY HAY IN STEERS

Eight ruminally fistulated steers (711 kg +/- 72 kg) were used in a cr ossover experimental design to study the nutritional effects of macera ting timothy grass (M) over the conventional conditioning process (C). Maceration was applied at mowing by conditioning the freshly cut fora ge through eight high-speed metallic grinding rolls with a shredding e ffect on leaves and stems. Animals were fed an all forage diet consist ing of M or C. Feces were collected over a period of 6 d for total dig estibility determination. On day 7 of each experimental period, rumina l fluid was sampled at 0, 1, 2, 4, 8 and 12 h after meals. On days 9-1 1, nylon bags were incubated in the rumen of each steer for 4, 8, 12, 24 and 48 h in order to determine forage dry matter (DM) degradation a t the ruminal level. Maceration reduced the field drying time to reach baling moisture by 50% under Southeast Canadian climatic conditions. Results of forage digestibility at the ruminal level showed that the r ate of forage DM disappearance was greater (P<0.001) for M than for C. This greater ruminal digestibility of M was associated with numerical ly although not statistically greater ruminal concentrations of acetat e, propionate and butyrate at all sampling times in steers fed M. Howe ver, butyrate concentration was higher (P<0.05) in M fed animals than in C fed animals, at the 4 h sampling. Although M was better digested at the ruminal level, total digestibility of DM, organic matter, ADF a nd NDF was slightly less for M than for C (P<0.05). Total digestibilit y of nitrogen was similar for both treatments. An increased passage ra te of M might explain its decreased total digestibility. This last ass umption still needs to be verified as well as the impact of this small decrease in digestibility on animal production.