Methane output from cows has been in focus of late, largely because of its high global warming potential.
However, Liam Sinclair, professor of animal science at Harper Adams University, says farmers can take steps to lower methane emissions by tweaking cow diets.
“There are discussions as to whether methane should be considered the same as other greenhouse gases (GHGs) like carbon dioxide due to its short life span,” he says.
“However, it is a very potent gas and can have a significant impact on climate change. So, reducing production levels should be a focus for dairy farmers looking to lessen their environmental impact – and one way of doing this is through nutrition.”
Below, Prof Sinclair details five ways farmers and nutritionists can make changes to diets to lower cows’ environmental footprint.
1. Choose ingredients to minimise methane production
It is important to consider forage and concentrates separately and look at how both feature in the diet as a starting point.
Methane will be greater in higher-yielding cows, however, the methane produced for each unit of milk will be less – and that is what the focus is on when it comes to reducing methane.
Feeding concentrates can increase milk yield – reducing methane for each litre of milk – and using specific ingredients can also help bring down overall levels of methane produced through the fermentation process in the rumen.
For example, incorporating starchy feeds results in more propionate in the rumen, which is associated with less methane production.
The science behind this is that having a greater proportion of propionate in the rumen minimises the volume of hydrogen available for methanogenesis – the process which generates methane.
Specific feed types to consider include cereal-based concentrates, as well as some peas and beans.
Experience shows you must be feeding a reasonably high level of concentrates to see a result – moving from 3kg to 4kg a cow a day is unlikely to produce a large result, whereas going from 12kg to 14kg a cow a day will make a difference.
Caution is advised with feeds such as soya hulls, which can lead to acetate fermentation. This produces greater volumes of hydrogen and, therefore, more methane.
Feeding larger volumes of concentrates can increase the risk of acidosis, so this should be monitored carefully, from both an animal welfare perspective and to avoid losing the benefits of increased starch.
2. Focus on forage quality and grazed grass
Similar principles apply for feeding forages, however, a specific focus on quality will help reduce methane produced for each litre of milk.
Better-quality, lower-fibre forages improve the rumen fermentation process and encourage better intakes – the latter of which will increase yields and, therefore, reduce the methane for each litre of milk.
The less fibrous the forage is, the more digestible it is, and, therefore, less methane is produced.
In terms of quality, farmers should aim for an optimum D-value of 70-75, as well as ensuring basic quality measures such as cutting at an early stage to preserve quality, observing good clamp management and avoiding spoilage.
Diets featuring maize are often associated with reduced methane, largely due to the high starch levels (up to 30%).
Grazed grass is also a useful dietary component. Studies show grass is more digestible than silage, but is also reasonably high in polyunsaturated oil – both of which are associated with reduced methane production.
3. Consider the benefits of feed additives
There are several additives available that can help reduce methane production. These often work by inhibiting the growth of methane-producing bacterium and getting rid of hydrogen in the rumen.
Sources include garlic oil/extract, as well as linseed oil and tannins such as those found naturally in clover.
A very exciting development is 3-nitrooxypropanol – a compound that has been specifically designed to inhibit methane. Studies so far have shown it can reduce methane in the rumen by 15-30%. It is expected to be available to farmers soon.
The downside is there is a cost to including additives in the diet and, undoubtedly, farmers will want to see a tangible benefit from their investment.
At present, there is no market force to specifically instruct farmers to reduce methane, so there is less of an incentive to do so.
It is likely we will see more of these products on the market in the coming years. But one potential benefit is that reducing energy loss through methane production might also result in higher milk yield or growth rates.
4. Manage rumen passage rate
The idea behind managing the feed passage rate through the rumen to reduce methane is simple – the less time feed spends in the rumen, the less methane is produced.
Achieving this is two-fold. First, the more cows eat, the quicker it will come out. So farmers should provide good-quality, fresh, palatable feed.
There are also practical elements to consider such as ensuring feed is pushed up often and there is sufficient feeding space – simple things like this will really help to increase the passage rate.
Second, diets composed of highly digestible nutrients will increase the passage rate. This will arguably have the biggest effect, so ensure the diet is well-mixed and cows cannot sort through the feed.
A poorly mixed ration will only hinder intake. Previous studies show that 66% of farmers feeding mixed rations have significant diet selection issues.
Looking at feed intake from a more holistic point of view, ensuring animals are in good health and are not lame will also help.
5. Put a greater emphasis on heifer management
An area that is often overlooked when considering on-farm methane production is replacement heifers.
Often heifers are the greatest contributors to total herd emissions. This is because heifers produce methane for two years but no milk – the result is an extremely high methane/litre of milk calculation.
Therefore, it is critical to ensure heifers calve at 24 months to bring this figure down. The UK average age of first calving is about 27-29 months – this will be having a significant effect on overall UK dairy farm methane levels.
Nutrition also plays a key role here, so ensure replacement heifers have a well-formulated diet to meet weight and growth targets.