Around 45% of a dairy farm’s carbon footprint (CFP) stems from enteric methane production from the natural process of feed digestion. However, there are many things that can be done nutritionally to help reduce methane production, as well as lowering your CFP through small changes to forage management and purchased feed usage.

Methane is produced in the rumen as a result of cellulose digestion. The more fibrous the feed, the higher the cellulose content and the more methane produced.

Therefore, improving the digestibility of forages will reduce enteric methane emissions. The digestibility of silage can be improved (and the fibre content or NDF reduced) by cutting grass earlier when it is less mature. This will help raise the metabolisable energy (ME) and protein content. The other benefit of improving the nutritional value of the silage is a higher milk output and more milk from forage. Alternatively, concentrate use can be reduced to achieve the same level of output.

Either way there are benefits to the intensity of your CFP by having more kgs of milk to spread emissions over, bearing in mind a farm’s CFP is expressed as kg CO2e/kg fat and protein corrected milk.

Read more: No clear evidence how best to reduce dairy GHGs – John Harvey

If using less concentrates, there is a reduction in the embedded carbon emissions generated by growing, processing and transporting imported feeds. Improving grassland management can also help through rotational grazing practices, with the aim of grazing livestock on more nutritious swards, growing more grass and utilising it more effectively compared to set stocking systems.

The type of forage can also have an influence on methane production. Herbal leys, which include a combination of grasses, legumes and herbs, are thought to produce less methane compared to predominantly perennial ryegrass swards.

Lucerne and herbs such as sainfoin and birdsfoot trefoil contain tannins that affect microbial fermentation in the rumen, reducing methane production.

Substituting grass silage with maize silage can also have a positive effect on methane output. Research carried out by the University of Reading showed that the higher the inclusion of maize silage in the diet, the greater the dry matter intake and milk yield, with a lower methane yield (g/kg of dry matter intake), compared to cows fed high grass silage diets.

Embedded emissions in purchased feeds can contribute around 20% of emissions to a farm’s CFP depending on the farm management regime. An obvious win is removing soya from the diet, but farmers could also consider other protein sources.

Home-grown sources such as peas and beans will be favourable over purchased protein, despite associated emissions to grow and harvest these crops.

By-products generally have a lower CFP associated with them; however, it will depend on their form and dry matter. For example, distillers dark grains take significant amounts of energy to dry and pellet the product, and therefore its carbon equivalent will overall be much greater than moist co-products, even though they will be fed at a higher rate.

There are a number of feed additives which claim to reduce methane emissions, based on combinations of essential oils. They also claim to have benefits of improved feed conversion efficiency and better protein utilisation, which will help improve the efficiency of milk production, either producing more milk or the same amount with less inputs. Either way, carbon emissions per kg of product will be reduced.

The industry is eagerly awaiting the arrival of 3-NOP (3-nitrooxypropanol) on the market which claims to reduce methane emissions in dairy cows by up to 30%. It works by inhibiting the enzyme responsible for methane production in the rumen. Small improvements in feed efficiency have been reported, with higher milk fat yields (Melgar et al., 2020).

Feed additives to reduce methane production are a significant development in the fight against climate change and it will be interesting to see whether in time, farmers are put under pressure to use such additives, which will incur a cost.

However, the bigger picture is that the industry must be seen to be doing all it can to reduce emissions and improve the environmental credentials of dairy farming. The various nutritional strategies outlined above are just some of the ways farmers can contribute towards the net zero goal.