1524
A larger proportion of grass feed components in the ration was associated with higher methane production rates of dairy cows
Ruminants can utilize feedstuffs which are not in competition with human food. In 10 German Holstein cows, 4 in 1st (L1; BW 562 kg) and 6 in 2nd(L2; BW 615 kg) lactation, 2 TMR rations fed ad lib were compared in regard to methane production. Ration 1 (R1) contained a mixture of grass silage, grass hay + straw (total of 22% DM), and corn silage (32% DM), and was fed to all cows from 20-103 DIM. Subsequently, from 104-140 DIM, cows received ration 2 (R2), comprising 41% DM of the grass silage, grass hay + straw mixture, and 18% DM of corn silage. Starch, fat and energy contents of R1 and R2 were 18, 4.5% DM, and 7.2 MJ NEL/kg, and 10, 2.7% DM, and 6.7 MJ NEL/kg, respectively. Water was offered ad lib. Appropriately acclimatized cows were measured in respiration chambers (1) on 99 and 135 DIM for 36 h. The respective rations and water were provided ad lib. DMI, ECM yield, and methane production per d were determined. Data was analysed by PROC MIXED of SAS. DMI did not differ among rations and lactation number (P > 0.1). However, ECM was lower with R2 (L1: 23.3. vs. L2: 29.2 kg/d) than with R1 (L1: 30.9 vs. L2: 36.3 kg/d) as well as in L1 than in L2 cows (P < 0.05). Methane production was affected by ration but not by BW or lactation number with higher values in cows fed TMR with higher contents of grass components and lower proportions of corn silage (R2 vs. R1: 513 vs.455 L/d; 18 vs. 12 L/(kg ECM * d); 39 vs. 34 L/(kg DM * d); P < 0.05). In conclusion, using larger amounts of feedstuffs less in competition with human food, i.e. grass and straw, contributes relatively more to greenhouse gas emissions. The lower ECM yield with R2 was partly due to progressing stage of lactation.
(1) Derno et al. J. Dairy Sci. 92:2804-2808, 2009.
Keywords: dairy cow, starch content, methane emission