Nitrous oxide adds to greenhouse emissions, but a test on a strand of a cow’s tail could make a difference

Where cattle are concerned, methane is well recognised as a contributing factor to climate change but scientists have long recognised nitrous oxide from the dung and urine of cattle is also a major source of greenhouse gas emissions in Australia.

Nitrous oxide is more than 300 times more efficient at trapping heat in the atmosphere than carbon dioxide.

But just as farts and burps vary in cattle and people, so do the amount of urine a cow can produce – and the percentage of nitrogen within that urine.

University of Queensland (UQ) researchers have now found a simple way to identify nitrogen-efficient cattle, with the added bonus that cattle who are good at recycling nitrogen are also likely to pass along the gene.

A collaborative project between the UQ’s Queensland Alliance for Agriculture and Food Innovation (QAAFI), the Queensland Department of Agriculture and Fisheries, and the Meat & Livestock Australia Donor Company has been testing the method on brahman cattle at Gatton in south-east Queensland.

Led by Associate Professor Luis Prada e Silva, the team has found a way to use a small piece of hair from the animal’s tail to identify its ability to recycle nitrogen.

“Selecting animals that are more efficient in using nitrogen would be very useful to increase performance in low protein diets, such as during the dry months in the north,” Dr Prada e Silva says. 

“We have demonstrated that the efficiency of the animals is related to their ability to maintain high nitrogen in the body and not lose that in the urine.

“This trait has about 40 per cent heritability, which opens a new door for genetic selection.”

This study and previous worldwide research has revealed a “massive” variation in the nitrogen recycling ability of cattle.

“Some animals are really amazing,” Prada e Silva says. “They can lose only 20 percent of the nitrogen they eat, while some animals lose 60-70 percent.

“On average, a beef cow has a nitrogen efficiency of only about 10 percent. A dairy cow has about 25 percent nitrogen efficiency and a feedlot-intensive growth steer will also have around 20-25 percent efficiency. That applies across all livestock species.”

Selective breeding on the basis of nitrogen efficiency could not only lead to healthier animals in dry climates, but more market-ready animals would minimise the number of livestock needed.

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Prada e Silva says this would have implications for both the nitrogen and methane production of livestock. Fewer animals means less greenhouse gases.

He says the current agricultural spotlight is on decreasing the amount of protein fed to livestock to reduce the amount of nitrogen in the dung and urine.

“In the pig and poultry industries, there is a bigger focus on decreasing the total amount of protein by using synthetic amino acids or making the diet more efficient because that will reduce the impact on the environment,” Prada e Silva says.

“We are not there yet with cattle, but Europe and other countries are already under pressure to decrease the environmental impact of livestock production.”

The identification of nitrogen-efficient, high-performance cattle could assist in reducing protein supplements.

Prada e Silva says the breakthrough in the team’s research is in the simple method of measuring an animal’s nitrogen-recycling efficiency through testing of hair from the animal’s tail.

They will now validate the results with a large sample herd and measure the performance of the animals over a three-year period.

The researchers are also attempting to identify the DNA markers associated with nitrogen efficiency and are looking to commercialise their findings.

“There are still questions that need to be answered, but the next step is to find a commercial partner to take this into the market and make it available to the beef cattle industry in Australia,” he said.