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Are cows more than a wee problem for the environment?

Guest Blog – Stuart Kirwan. Stuart is based in the Animal Nutrition Building on the UCD Lyons Research Farm where he is doing his PhD.


Irish agriculture faces a major challenge in regards to climate change, in how it deals with greenhouse gases (GHG) emissions transboundary gases/air pollutants such as ammonia. In Ireland the agriculture sector was directly responsible for 32.2% of national Greenhouse Gases (GHGs) emissions in 2016, mainly methane from livestock, and nitrous oxide due to the use of nitrogen fertiliser and manure management.

The agricultural sector is the largest source of ammonia emissions in Ireland and accounts for 98% of total emissions, of this, the cattle sector accounts for 80%. Ammonia impacts on environmental sustainability as it can lead to eutrophication of nearby water courses, have negative impacts on natural habitats and react with other pollutants to produce aerosols which can lead to significant negative impacts on human health and the environment.

The trend in ammonia emissions is largely determined by the cattle population. Ireland has obligations under the National Emissions Ceiling Directive to achieve reductions for ammonia by 1% 2020 and by 5% 2030. Given that ammonia emissions are largely determined by cattle numbers and with an increase in the national dairy herd since the abolition of milk quotas in 2015, this poses are real challenge for Ireland in achieving these targets.

Cattle are inefficient users of the nitrogen they consume in their diet, using only 10-30% of what is ingested with the remainder excreted in urine and faeces. The loss of nitrogen as ammonia in animal excreta occurs when urea (form of nitrogen in the urine) is volatized (broken down and released as a gas) by the enzyme urease, which is abundantly available in the faeces following deposition from livestock during housing, manure storage and land application and when animals are grazing.

Going forward, reductions in ammonia emissions can be achieved by better efficiencies and the adoption of new slurry handling techniques at farm level. Farmers that can reduce the protein content in their animal’s diets to match their requirements can reduce the amount of nitrogen excreted in the environment while also saving on the amount spent on purchased feed. Extending the grazing season is an abatement strategy to reduce ammonia emissions. By extending the grazing season, the housing period is shortened with less volumes of slurry and manure produced, hence reducing the total emissions from housing and storage. The acidification of slurry has the potential to reduce ammonia emissions from housing, storage and field applications. Also, the timing of slurry application has an effect to the extent of nitrogen lost as ammonia. Analysis has shown that during the calendar year, the months from May to August present the greatest risk for increased ammonia emissions in Ireland.

Ongoing research is looking at ways to increase the nitrogen efficiency in cattle. Some of this research is investigating the effects of feeding different carbohydrate sources and the effect they have on nitrogen utilisation within the animal. Alongside this, research is also being conducted into the use of alternative natural feed ingredients (natural plant oils, seaweed extracts) and their effect on nitrogen metabolism within the animal. While some of this research is in its infancy, early laboratory studies have shown promising results, the next step is to see if this will carry through in the live animal.

The next challenge for Ireland is to implement policies and behavioural change that will allow Irish agriculture to operate in a more sustainable manner into the future.

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