Effects of maceration at mowing on digestibility and ruminal fermentation of timothy hay in steers

Abstract

Eight ruminally fistulated steers (711 kg ± 72 kg) were used in a crossover experimental design to study the nutritional effects of macerating timothy grass (M) over the conventional conditioning process (C). Maceration was applied at mowing by conditioning the freshly cut forage through eight high-speed metallic grinding rolls with a shredding effect on leaves and stems. Animals were fed an all forage diet consisting of M or C. Feces were collected over a period of 6 d for total digestibility determination. On day 7 of each experimental period, ruminal fluid was sampled at 0, 1, 2, 4, 8 and 12 h after meals. On days 9–11, 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 at 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 rate of forage DM disappearance was greater (P < 0.001) for M than for C. This greater ruminal digestibility of M was associated with numerically although not statistically greater ruminal concentrations of acetate, propionate and butyrate at all sampling times in steers fed M. However, 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 and NDF was slightly less for M than for C (P < 0.05). Total digestibility of nitrogen was similar for both treatments. An increased passage rate of M might explain its decreased total digestibility. This last assumption still needs to be verified as well as the impact of this small decrease in digestibility on animal production. Key words: Maceration, digestibility, ruminal fermentation, steer, forage, grass