Selecting the right animals can lead to significant reductions in nitrate leaching and nitrous oxide emissions, according to research at Lincoln University’s Pastoral Livestock Production Lab.
The findings show that cows with lower amounts of urea in their milk have a correspondingly lower level of urea in their urine and that cows at the lower end of the scale leach up to 40kg/year less nitrate than cows at the top end of the scale.
PhD student Cameron Marshall did the experiment as part of his thesis, using cows on Lincoln University’s Ashley Dene research and development station identified by CRV Ambreed as having low breeding values for milk urea, to test the hypothesis that these animals also have lower levels of nitrogen in their urine.
“Theoretically, they should have less urea in their urine, but previously it had only been hypothesised and we were first to come along and prove that,” Marshall says.
For the experiment, 24 animals that were low for this breeding value and 24 that were high were compared, with urine samples being taken several times a day for analysis.
“We were trying to make sure that these animals that have been assigned as low do indeed have less urea in their urine and that’s what we found.
“From the lowest to highest, there was a 40kg/cow/year difference in the amount of nitrates leached based purely on genetics,” he says.
“Nitrate leaching is the key environmental concern, so if you were to target and lower these values more for your entire herd, you can theoretically reduce your nitrate leaching by quite a lot.”
A one unit decrease in the milk urea nitrogen breeding value would result in a 240 kg/ha/year reduction in the amount of urinary urea nitrogen deposited to pasture.
By selecting animals with low milk urea nitrogen breeding values, this characteristic could be bred into the herd.
“There’s a massive environmental affect and one of the other things is less urea in the urine will result in less nitrous oxide being emitted, which is a really potent greenhouse gas, so on two fronts you’re breeding an animal that’s more environmentally friendly,” he says.
And it turns out there’s a positive effect on production as well, with more protein in the milk of the low nitrogen-peeing cows.
“Effectively, we can breed for an animal that is not only more environmentally friendly but also more productive so you can get paid more for a reduced environmental impact. To me it’s a no-brainer – then again, it’s my research, so I’m biased,” he says.
The research project was conducted in Lincoln’s Pastoral Livestock Production Lab, part of the University’s Faculty of Agricultural and Life Sciences, led by Professor Pablo Gregorini.
Gregorini is from Argentina and has been in New Zealand for 13 years, and previously worked for Wageningen University in the Netherlands, the Department of Agriculture in the US and the Institute of Grasslands and Environmental Research in the UK, as well as DairyNZ.
He says Marshall’s findings are important because they show that something as simple as selecting the right animal for the job can pay enormous environmental dividends.
