Hellwing, Anne Louise Frydendahl4; Weisbjerg, Martin Riis4
1 Animal nutrition and environmental impact, Faculty of Agricultural Sciences, Aarhus University, Aarhus University2 Department of Animal Health and Bioscience, Faculty of Agricultural Sciences, Aarhus University, Aarhus University3 Department of Animal Science - Animal nutrition and physiology, Department of Animal Science, Science and Technology, Aarhus University4 Department of Animal Science - Animal nutrition and physiology, Department of Animal Science, Science and Technology, Aarhus University
That methane emission from dairy cows is affected by concentrate to forage ratio is well known, whereas the effect of the quality of grass-clover silage is not well described. Besides this the purpose of the present study also was to test our new facilities for measuring methane emission from dairy cows and the working routines. Twenty-four Holstein cows were allocated to eight different treatments and blocked according to parity. Treatments were in a 2x4 design, 2 concentrate to forage ratios and four different grass-clover silages. The grass-clover silages (A, B, C, D) were produced during the growth season 2009. A was primary growth made in the beginning of May, B second 1st regrowth made in middle of June, C was 3rd regrowth made in the beginning of August and D was 3rd regrowth made in the end of August. The energy concentrations were 6.6, 6.0, 6.5 and 6.1 MJ NEL/kg DM for silage A, B, C and D, respectively. TMR forage DM consisted of 2/3 of one of the respective grass-clover silages and 1/3 maize silage, and concentrate (soya meal and wheat) proportion of DM was 20% (low) or 50% (high). Methane emissions from the cows were measured 20-22 hours in one of four chambers working after the principles for indirect calorimetry The air flow was measured continuously, and the concentration of methane, oxygen and carbon dioxide were measured in ingoing and outgoing air from the chambers every twelve and half minute. The cows were milked and feed twice daily, and yield and intake were registered. The experiment was analyzed as a 2*4 factorial design with parity as block effect. The methane emissions as total emission and per kg milk yield were significantly affected by concentrate proportion, but not by silage type. Cows on the high concentrate diets produced in average 617 liters of methane and cows on the low concentrate diet 770 liters of methane per 24 hours. The experiment showed that the system worked and measured reliable values for methane emission in relation to diets and feed intake, although accuracy of relating methane emission to feed intake was hampered by the short 20-22 hours chamber measuring periods.