Helping the climate: A diet containing milled rapeseed reduces the methane eructated by cattle

In addition to reducing methane emissions, the new diet decreased the proportion of saturated fatty acids in milk – without reducing milk output.

Bovine methane emissions as a factor contributing to the climate crisis have been under the magnifying glass for a long time. In fact, researchers across the globe are looking for ways to reduce the amount of methane escaping to the atmosphere. In practice this means fine-tuning diets, as methane is produced in the rumen, the first of the four stomachs of cows, from where they emit the gas into the air by eructation.

“In other words, it doesn’t exit from the back, which is something that comes as a surprise to many,” chuckles Anni Halmemies-Beauchet-Filleau, a university researcher specialised in cow diets at the Faculty of Agriculture and Forestry, University of Helsinki.

Within an international project studying if the ruminal methane emission can be decreased and milk far composition of dairy cows improved by plant lipids, Halmemies-Beauchet-Filleau has gained promising research results by feeding milled rapeseed and grain in addition to a diet based on AIV feed that is the acid-preserved grass silage traditionally used in Finland, to the roughly 60-strong dairy herd at the University’s teaching and research farm in Helsinki.

The cows whose diet included milled rapeseed emitted as much as one-fifth less methane and one-third less hydrogen compared to cows on the conventional diet, whose protein feed constituted of low-fat rapeseed meal.

Milled rapeseed, rich in oil, also altered the milk fat composition by decreasing the amount of saturated fatty acids in milk by one-fifth. However, no reduction was seen in either milk output or the fat concentration of milk, and there were no changes in the cows’ overall condition compared to the prior diet.

“To cows, methane is purely a by-product, or energy escaping from the feed to the air. Having part of the energy content of feed disappear into thin air doesn’t benefit farmers either,” says Halmemies-Beauchet-Filleau.

The feed formula has been specifically adjusted to Finnish conditions, as globally the basic feed of cows varies greatly outside fibre-rich grass silage. Lipid-rich rapeseed does not function as well with, for example, starch-rich corn silage, as the combination contains an insufficient amount of fibre to support the rumen’s wellbeing. Soy feeds are typically used in other countries, but in Finland they are not used in the diet of dairy cattle.

In Finland, research projects with other oil plants suitable for supplementing grass silage have also been carried out. Anni Halmemies-Beauchet-Filleau mentions false flax, better known as camelina, under the Brassicaceae family of plants.

“It might be easier to farm than turnip rape or rapeseed, since as a more indigenous species it has better resistance against diseases and pests. It also has the potential for yields equivalent to those of turnip rape. In fact, it would be interesting to further investigate the potential of camelina feeds,” Halmemies-Beauchet-Filleau envisions.

Project Dairy products with reduced saturated fatty acids has been funded by EIT Food, part of the Horizon 2020 programme of the European Union.

Turnip rape or rapeseed? Seed, meal or cake?

Turnip rape and rapeseed are cruciferous plants and relatives of the turnip. In Finland, both are referred to as turnip rape in conjunction with animal feed use, as their nutrient concentrations differ only to an insignificant degree. The oil concentration of whole seeds is approximately 40%.

Finland is not self-sufficient in farming these two plants; the protein-rich rapeseed meal from which the oil has been solvent-extracted is imported mainly from central and southern Europe as well as South America. Instead, Finland produces turnip rape and rapeseed cakes, from which the oil has been extracted by pressing, leaving the lipid concentration higher compared to meal.

In 2019 the total area sown with turnip rape and rapeseed in Finland was the smallest in 40 years, with both crops sown in roughly equal areas (Natural Resources Institute Finland, Utilised Agricultural Area 2019, preliminary data). The cultivation period of rapeseed is more than a week longer than that of turnip rape, which is why it is mainly grown in southern Finland.

Both turnip rape and rapeseed are self-fertile, which means that they are able to create oil-rich seeds by pollinating each flower with its own pollen. Cross-pollination with the pollen of other plants with the help of the wind or insect pollinators improves the yield. Turnip rape and rapeseed are favoured by bees.