Methane (CH₄) consists of carbon (C) and hydrogen (H) and is a powerful greenhouse gas with an effect that is 25–28 times higher than the effect of carbon dioxide. Methane is formed as a natural part of the microbial fermentation in the rumen, from hydrogen and carbon dioxide, both of which are final products from the fermentation of carbohydrate in the rumen. A high-performance Danish dairy cow produces about 750 litres of methane per day, which corresponds to a loss of approx. 6% of the feed content of the gross energy.

However, the methane production in the rumen of cattle can be reduced for example by adding fat to the ration or by adding a new feed additive, Bovaer®, developed by the company Royal DSM in the Netherlands. However, it is unclear whether the lower production of methane means that more carbon and hydrogen are lost in the form of exhalation of for example carbon dioxide, hydrogen and hydrogen sulphide or if there is more carbon and hydrogen actually available for the animal's metabolism, and where that carbon and hydrogen subsequently end up.

Can cows benefit from the excess carbon and hydrogen?

A new feeding experiment at AU Foulum is to shed light on this question. “Carbon and hydrogen exhaled in the form of carbon dioxide and hydrogen, respectively, have no value for the cow. However, if it is included in the formation of microbial protein and volatile fatty acids, such as acetic acid, propionic acid and butyric acid, which the cow can subsequently utilise, then it will be positive for the animal's energy and nutrient supply. Therefore, we need more knowledge about the positive and possible negative consequences of a reduction in the production of methane in the rumen compared to the animal's supply of energy and nutrients”, says Professor Peter Lund from the Department of Animal Science at Aarhus University, who is at the head of the experiment.

Effect of methane-inhibiting measures on cows’ nutrient supply

The new feed additive Bovaer® – also known as 3-NOP – has been studied in a wide range of countries in dairy cows, beef cattle, calves and other ruminants. The substance works by inhibiting an enzyme that contributes to the latter part of the methane formation in the rumen. The studies show that the dairy cows' methane emissions are reduced by an average of approx. 30% when the substance is added to the cattle's daily feed ration. The feed additive is expected to be approved by the EU late 2020/early 2021, after which it will be marketed throughout the EU, including in Denmark.

Previous experiments at AU Foulum have shown that more fat in the feed can reduce the release of methane from the cows' digestion by up to 10%. However, the researchers must now investigate further how extra fat allocation and the inclusion of Bovaer® affect the animal's supply of nutrients in the new feeding experiment.

The experiment in AU Foulum's cattle experimental facilities

The experiment, which is carried out in AU Foulum's cattle experimental facilities, includes 4 Holstein cows. The following treatments are included in the experiment:

1. Control
2. Adding extra fat to the ration
3. Adding Bovaer® to the ration
4. Adding extra fat and Bovaer® to the ration

During the experiment, researchers will collect data on the cows' feed intake, fermentation profile in the rumen, microbial protein synthesis, nutrient utilisation in the different sections of the gastrointestinal tract, milk production, and milk composition. During the trial, the amount of methane, hydrogen, hydrogen sulphide, and carbon dioxide in the exhalation air from each cow will also be analysed.

“In addition to investigating what happens to the amount of carbon and hydrogen that is no longer included in the formation of methane, we will also get data on the methane-reducing effect of fat and Bovaer® separately and simultaneously under Danish conditions. These are currently two of the most promising strategies for reducing the production of methane from dairy cows”, concludes Peter Lund.

Facts about the project