Milk Index

• High quality forage reduces undesirable methane emissions
• Calculated reductions in methane losses for milk index varieties compared to other tested varieties vary between 4.6 % for a ration composed of grass silage, maize silage and concentrates up to 8.4 % for a grazing ration of grass and concentrates

Scientific research has shown that improving the forage quality of grass by means of a lower cell wall fraction and increased digestibility also contributes to the reduction of undesirable methane emissions. Quality results from forage trials conducted at different locations confirm the high digestibility of the Milk Index varieties (e.g. AstonEnergy).

Methane emission from dairy cows contributes to global warming. The production of methane (CH ₄) in rumen fermentation also represents a significant loss of dietary energy for the dairy cow. Therefore, reducing methane emissions from dairy cows has environmental as well as economic benefits.

Dairy cows are able to convert fibrous plant material into high quality animal products such as milk. To achieve this dairy cows depend on microbial fermentation in the rumen to digest their feed. The fermentation yields energy for the microbes and the resulting fermentation end-products, volatile fatty acids, are absorbed by the cow and used as its main energy source. Methane production (from carbon dioxide and hydrogen) is a natural by-product of fermentation and its production serves to remove excess hydrogen from the rumen. The type of volatile fatty acid produced in fermentation strongly determines the excess of hydrogen (and as a consequence the amount of methane) produced in the rumen. Excess hydrogen is produced together with the production of acetate and butyrate but not with the production of propionate.

Forage constitutes a large part of the ration fed to dairy cows. Specifically the fermentation of the cell wall fraction of forage gives rise to methane production in the rumen. The cell wall fraction of grass is composed of cellulose, hemicellulose and lignin. Fermentation of cellulose and hemicellulose yields predominantly acetate and butyrate, which stimulate methane production. Hence, the amount of methane produced by dairy cows can be reduced by lowering the cellulose and hemicellulose content of grass.

Not only a lowered cell wall fraction but also an increased digestibility potentially reduces methane formation in the rumen. In general, a higher digestibility is associated with acceleration of rumen passage, which, due to a shorter retention time in the rumen, depresses cell wall degradation. Moreover, high digestion rates will lower ruminal pH, which inhibits the growth of cell wall degrading bacteria favouring a higher propionate relative to acetate and butyrate production. In conclusion, improving forage quality of grass by means of a lower cell wall fraction and increased digestibility could contribute to reducing undesirable methane losses from dairy cows.