Fermentation of hammermilled barley, lupin, pea and faba bean grain in the rumen of dairy cows

Abstract

Four lactating Friesian cows fitted with rumen cannulae were used in a 4 × 4 Latin square design experiment and fed on oaten hay ad libitum. Hammermilled lupin, pea, faba bean or barley grain, calculated to provide 70% of the total ration dry matter, was given twice daily via the rumen cannula. Rumen liquor was sampled at 0, 1, 2, 3, 4, 6, 8, 10 and 12 h after the grain was given at 08 00 h, and pH and the concentrations of ammonia-nitrogen, lactic, acetic, propionic and butyric acids measured. The rate of degradation of modified-acid-detergent fibre (MADF) was determined in milled oaten hay incubated in nylon bags in the rumen. When the cows were given hammermilled barley grain, rumen pH declined to a minimum value of 5.4, and from three to six hours after the grain was given rumen pH was significantly ( P < 0.05) lower than when the cows were given the legume grains. Rumen pH was maintained above 6.0 when the cows were given hammermilled lupin or faba bean grain. Rumen pH was generally reflected in rumen lactic acid concentration. Rumen ammonia-nitrogen concentration was significantly ( P < 0.05) higher at 0, 3, 4, 5, 6 and 8 h after the legume grains were given than after the barley grain. Differences between diets in the concentration of total volatile fatty acids and the proportions of volatile fatty acids were generally not significant. The rate of degradation of MADF in oaten hay tended to be less when the cows were given hammermilled barley or pea grain than when they were given lupin grain. Mean dry matter intake of oaten hay was significantly ( P < 0.05) higher when the cows were given the legume grains rather than the barley grain. It was concluded that giving high levels of hammermilled legume grains (especially lupins) rather than barley grain to dairy cows will result in rumen pH values and ammonia-nitrogen concentrations that are unlikely to cause significant depressions in the rate of fibre digestion or intake of cereal hay.