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Diurnal variations in enteric methane emissions from non-lactating dairy cows offered diets differing in forage to grain ratio
This experiment determined how level of dietary grain inclusion affected daily enteric methane emissions and their diurnal variation in dairy cows. Six mature non-lactating Holstein dairy cows were offered one of three diets with forage to grain ratios of 100:0 (F), 75:25 (M), and 50:50 (H). The forage portion of the diet consisted of 80% grass hay and 20% alfalfa hay (DM basis). The concentrate was a barley-corn based ration (DM=893 g/kg, CP=198 g/kg DM). Feed was offered three times daily at 0900, 1300, and 1700. The experiment was a replicated 3x3 Latin Square Design, with each animal receiving each of the three diets over the course of the three 5-week periods. Experimental diets were switched gradually during the first week of every period. This was followed by three weeks dietary adaptation. Sample collection and enteric methane output measurement were conducted on two separate days during the fifth week of every period. Rumen fluid was collected using a stomach tube and a fecal grab sample was taken to determine pH at 0830 and 1500 on the day preceding enteric methane output. An open-circuit hood calorimetric system was used to determine methane output over a 24 hour period.
Increasing the grain content of the diet decreased rumen pH (F=7.02, M=6.82, H=6.77, P < 0.01) and fecal pH (F=7.09, M= 6.85, H=6.66, P < 0.01) and increased DMI (F=12.2, M=14.3, H=16.6 kg/d, P < 0.01). Increasing the dietary grain content increased daily enteric methane emissions (F=361.6, M=423.0, H=445.0 L/Day, P < 0.01). However, when methane production was expressed per kilogram of DMI, increasing the dietary grain inclusion reduced daily emissions (F=29.8 L/kg DMI, M=29.7 L/kg DMI, H=27.2 L/kg DMI, P < 0.01). Methane emissions clearly exhibited a diurnal pattern which coincided with feeding events, irrespective of diet offered. The highest rate of methane production observed was concurrent with afternoon feeding at 1300 (0.38 L/min); while the lowest rate of methane production was observed two hours prior to morning feeding (0.20 L/min). The diurnal pattern differed among diets (P < 0.01). In conclusion, dietary grain inclusion increased daily methane production and altered the diurnal pattern of methane emission rate.
Keywords:
Cattle, enteric methane emission, grain to forage ratio