Protein in, ammonia out – the impact of cattle diet on emissions

In small doses, ammonia gas makes smelling salts effective but high levels of ammonia can be a health hazard and a pollutant.

In the United States, the Environmental Protection Agency has estimated that dairy farms contributed more than 20% of the ammonia emitted from animal husbandry operations last year.

A recent study has compiled and analysed data from 25 previous studies, focusing on factors that influence how much ammonia dairy barns emit.

The goal was to figure out which factors influence ammonia emissions in dairy barns and – ultimately – to lower the amount of ammonia being released from dairy facilities. Adeline Bougouin, lead author of the study, said this is important because ammonia poses several dangers.

In the confined spaces of many farm buildings in the US, high levels of ammonia can be a threat to animals. Ammonia is also linked to the respiratory problems in humans. In the environment, ammonia can damage terrestrial and aquatic ecosystems.

“Our work is important because it provides key information to farmers and farm advisers about potential ways to lower ammonia emissions,” says Bougouin, who was a researcher at Wageningen University in The Netherlands and is now working at the French National Institute for Agricultural Research.

But reducing the amount of ammonia being emitted from dairy farms is challenging. Farms are economic enterprises and a solution must fit with the bottom line.

“Farmers need concrete strategies that reduce the environmental impact of their farms but not their economic output,” says  Bougouin.

The studies she and her colleagues examined had catalogued several factors that influence how much ammonia dairy barns release. They looked at both environmental factors, such as seasons and temperature, as well as the diet and nutrition of the dairy cattle.

“We confirmed that both environmental factors and nutritional aspects significantly influence ammonia emissions from dairy barns,” says Bougouin.

Some of the factors influencing ammonia emission — such as seasons — are beyond a farmer’s control. Those that are not include  the amount of crude protein in the animals’ diet.

“Crude protein is a measurement of the total amount of nitrogen in feed,” says  Bougouin.

Nitrogen in the diet is not broken down efficiently by cattle. It is excreted as urea, mostly through urine. When urine and faeces mix, the urea is rapidly converted into ammonia, which is then released into the atmosphere.

Bougouin found that reducing the amount of crude protein slightly in a dairy cow’s diet reduced the amount of nitrogen in manure and urea in urine. And it did not affect milk yield. Reducing excess nitrogen in the diet could be an effective strategy to reduce ammonia emissions without affecting a farm’s bottom line.

Other factors that influence the amount of ammonia being released from dairy barns include the flooring systems, the amount of dry matter in dairy cattle feed, and milk yield per cow.

The findings come with some caveats.

“The emission rates we describe in the study may not represent whole-farm ammonia losses,” says  Bougouin.

“Emissions can also occur during manure storage or during composting and field application.

“We will need to study whole-farm ammonia losses,” says  Bougouin. “Then we can better understand how various systems in farms contribute to total ammonia emissions.”

Read more about  Bougouin’s research in Journal of Environmental Quality. The  USDA and University of California-Davis funded the research.



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