The nutrients contained in one glass of milk. Source: milk.co.uk
In the UK alone, dairy farming employs around 50,000 people either directly, or in supporting industries, in addition to a further 24,000 people working at processing sites. However, the dairy industry falls under much criticism regarding climate change and its contribution to global warming.
Dairy and climate change
Dairy cows have been implicated as a huge contributor to UK greenhouse gas (GHG) emissions, releasing large quantities of methane as a result of enteric fermentation in the rumen, and nitrous oxide during manure storage and management. There are also embedded GHG emissions (emissions imported into the system), including emissions from feed production for the dairy herd, artificial fertiliser production, fuel, electricity and bedding materials.
A typical carbon footprint of a UK dairy farm broken down by the source of emissions. Emissions include carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) converted to carbon dioxide equivalents (CO2e).
The UK dairy industry has made great progress towards improving its sustainability and has reduced its carbon footprint by 24% between 1990 and 2015, but further action needs to be taken to meet government legislation which legally commits the UK to a target of net zero for all GHG emissions by 2050. Furthermore, the National Farmers’ Union (NFU) has set the goal of reaching net zero by 2040.
How can UK dairy farmers reduce their emissions?
The most effective way to reduce GHG emissions is to improve the overall efficiency of dairy farms, which has the added benefit of reducing costs as well as the carbon footprint.
Husbandry methods, such as reducing herd replacement rate, calving heifers when younger, genetic selection for increased milk yield and fertility rates, and improving housing systems, grassland management and grazing systems, can all reduce the GHG emission intensity.
Dairy cow feeding
The way that dairy cattle are fed can have a large impact on the carbon footprint. Methane production is an inherent part of rumination (digestion), but the quantity of methane produced per litre of milk can be reduced through improving the concentrate and forage balance of the diet. This can be done by optimising the balance of grass and maize silage, adopting phase-feeding by milk yield, increasing the proportion of fat and oil in the diet, using high sugar content grasses (ryegrass), or using feed additives such as 3NOP (3-nitrooxypropanol), probiotics or nitrate in rations.
The source of feed is also very important: diets containing soya have very high embedded emissions associated with the land use change (deforestation) and transportation of the feed. Many farmers are often reluctant to move away from soya as it is such a good protein source for high yielding dairy cows, but alternatives with a lower carbon footprint, such as rumen protected rapeseed meal, are starting to be widely used with no compromise to productivity.
Dairy cow manure management and fertiliser use
Optimising the storage and use of manure and slurry (organic fertilisers) could also reduce dairy’s carbon footprint, especially if used to replace artificial fertilisers. Covering slurry and manure stores and acidifying slurry can help to reduce emissions during storage, whilst having the additional benefit of increasing the amount of nitrogen available as fertiliser when applied back to the land. Having an understanding of soil nitrogen content and analysing the nitrogen content of manures as part of a nutrient management plan can help to determine the amount of additional artificial fertiliser needed to meet crop requirements, and prevent excess nitrogen being applied.
Following other good manure management practices, such as slurry injection or band spreading techniques, ensuring manures are incorporated within 24 hours of spreading, calibrating spreading equipment, and shifting from autumn to spring application can all improve carbon footprints by limiting nitrogen losses from the system. The use of nitrification inhibitors can also have a positive impact by reducing nitrogen losses. The use of artificial nitrogen fertilisers can be further reduced by using clover or other legumes within grass swards to fix atmospheric nitrogen, and selecting a low carbon source artificial nitrogen fertiliser can reduce embedded emissions.
Zero-grazing dairy systems
Switching to a zero-grazing system could be a viable way to significantly improve efficiency and reduce the carbon footprint of some dairy farms. These systems are based on precision agriculture and require a large investment; they must be carefully designed to maximise productivity whilst avoiding animal welfare concerns. The objective behind zero-grazing is to optimise the use of forage within the dairy cow diet through precision management of the grazing land and feeding of a total mixed ration (TMR) based on high-quality forages with concentrate supplements. In addition, there are no emissions from manure deposited whilst grazing, cows have a reduced energy requirement for activity and milk yields are often increased.
Silvopastoral dairy systems
Silvopastoral systems take an integrated approach and require a transformational change in dairy farming practices, combining fodder plants, shrubs and trees on grazing areas (see Figure 4). The idea behind these systems originates from traditional farming methods in South America, but have been successfully applied in modern dairy systems within Europe and the UK. Benefits include an increase in carbon capture and storage, improved soil health, and improved animal welfare and resilience through the provision of natural shelter for the cows.
This type of management system is not feasible for all dairy producers, but could improve the sustainability of lower yielding herds, and provide a grazing option for the youngstock and dry cows in higher yielding herds.
Schematic of a silvopastoral dairy system. Adapted from Solorio et al. 2016
How can ADAS help?
No two dairy farms are the same, and therefore mitigation strategies need to be developed according to the individual GHG emission hotspots for each farmer, the resources they have available, and the policy requirements of any schemes they are engaged in. Companies developing climate change or environmental strategies also need to be aware of this.
ADAS help companies engage with their agricultural supply chain to understand GHG emission sources. Our work spans from company strategy through to on-farm mitigation. We support companies in developing science-based targets and supplier engagement strategies. We can also work with farmers to measure emissions and take action to mitigate climate change. Contact firstname.lastname@example.org for more information or see our key services here.