A federal researcher is trying to find out why manure smells.
“Corn smells a little better in feedlot manure than barley and in the last two years there has been a lot of corn fed in southern Alberta, but I’m not sure the province smells any better overall because of it,” says Sean McGinn of Agriculture Canada’s research centre in Lethbridge.
McGinn and his colleagues are studying livestock odour in hopes of finding solutions that will help ease relations between livestock producers and their neighbours.
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McGinn said corn produces less odour than barley because of its lower protein to carbohydrate ratio.
Urinary urea accounts for half of the total nitrogen excreted by cattle and urea accounts for half of manure’s odour.
Urea starts out as protein, which is then converted in the rumen to ammonia. Rumen microbes use the ammonia to create the amino acids that cattle need to grow.
The microbes need to feed on carbohydrates. If there isn’t enough, the microbes stop reproducing as they run out of food. The unused ammonia is then absorbed by the blood and excreted as urea in the urine, which smells.
McGinn said feeding corn or blended feed rations to feeder cattle that have lower protein-to-carbohydrate ratios will cut ammonia production and some odour.
But urea has an equally stinky partner.
McGinn has found new information that shows volatile fatty acids must take much of the blame for odour.
The main culprits in livestock manure include ammonia, hydrogen sulfide, amines, mercaptans, volatile fatty acids and phenols.
McGinn’s team set up air sampling equipment 100 and 200 metres away from four southern Alberta feedlots last summer, either adjacent to or downwind from the lots.
“People have often blamed the odour on ammonia, but in fact the volatile fatty acids have a greater role to play, especially butyric acid,” McGinn said.
He said the test results will help him and other scientists find ways of controlling manure odour.
It’s not known how diet and other production methods can reduce the release of these volatile fatty acids, but the research gives scientists additional compounds to examine in future studies.
“Incorporation into the soil immediately after it is applied to fields will help,” he said.
“But light irrigation was the best – six millimetres of water on freshly spread material. Irrigation for half to an hour reduced odour by 20 percent, and was the best control we found.”
