R&D scientist finds genetic link for nitrogen leaching

Phil Beatson

CRV Ambreed’s genetic discovery that could help reduce nitrogen leaching on New Zealand farms by 20% within 20 years is thanks to the company’s R&D scientist Phil Beatson.


Mr Beatson says over the past five years CRV Ambreed has investigated what could be done with genetics to reduce the amount of nitrogen excreted as urine. Nitrogen taken in by cows in their diet is converted into five areas:  Milk protein (+ urea); growth (muscle is protein); dung; gases; and urine. “From an environmental perspective, we saw urine as being the big issue because of its impact on water quality,” Mr Beatson says.


Now, in what’s thought to be an international first, the dairy herd improvement company has announced it will market semen from more than 20 existing, high-performing bulls under a LowN Sires brand. These bulls are desirable for traditional traits as well as being genetically superior in their ability to reduce concentration of Milk Urea Nitrogen (MUN) in their daughters.


MUN is a measure of the amount of nitrogen contained as milk urea. Many farmers get a milk urea concentration report each day for their bulk milk sample. MUN is simply the nitrogen component of that milk urea.


Mr Beatson says there’s very strong international evidence of a direct connection between MUN and the amount of nitrogen excreted in urine when cows are fed varying diets. Cows with low MUN excrete less nitrogen as urine.


Mr Beatson and the CRV Ambreed genetic research team has investigated the genetics of MUN. The rationale has been that if it’s possible to reduce MUN through traditional genetic selection means, and providing the relationship between MUN and amount of nitrogen excreted in urine holds, then the genetically improved animals for MUN will excrete less urinary nitrogen and hence leaching per animal and per hectare can be reduced.


“Cows bred for lower levels of MUN are expected to excrete less nitrogen in their urine which will, in turn, reduce the amount of nitrogen leached from grazed pasture,” he says.


“It could potentially save New Zealand 10 million kilograms in nitrogen leaching a year within 10 years, based on the national herd number of 6.5 million dairy cattle. Modelling suggests that farmers who start a breeding programme for low-MUN now could reduce nitrogen leaching by 10-12% by 2025.”


The primary cause of nitrogen leached into the ground and waterways comes from the cow’s urine being concentrated in relatively small patches. Some of the nitrogen excreted is converted to gas, some is taken up by plants, and a substantial amount is leached, with soil-type affecting the proportion that is leached.


International research shows the link between MUN and lower nitrogen output in urine. And other genetic studies have found that MUN is a heritable trait and have even stated that it is possible to reduce MUN through genetic selection. But that avenue has not been pursued overseas where alternative farming systems mean cows are not on pasture as much as they are in New Zealand and nitrogen leaching is possibly not as important an issue as it is here.


Mr Beatson’s research was designed to identify superior bulls for MUN with the specific aim being to provide low-MUN bulls to breed cows that excreted less nitrogen in their urine: in line with overseas studies he has identified some bulls that will breed daughters that have desired low levels of MUN, while at the other end of the scale some bulls will breed daughters with high levels of MUN.


CRV Ambreed will be the first organisation in New Zealand and possibly the world to market bulls with low MUN genetics with the aim being to provide a long-term genetic solution to nitrogen leaching.


Hundreds of thousands of straws of semen are now available from the LowN Sires team which has desirable genetic makeup for low levels of MUN. “It’s exciting news for farmers, knowing that they can reduce MUN and very likely can help meet their environmental compliance by breeding,” Mr Beatson says.


Since 2012, CRV Ambreed has measured MUN concentration in 650,000 milk samples and analysed them to understand how strongly the trait is inherited, and to create a MUN breeding value for all animals measured as well as sires of the cows.


Mr Beatson says farmers who already herd-test and herd-record with CRV Ambreed will automatically get the MUN values of their cows over the winter months. This will help with decisions around culling or keeping cows for AI using bulls with desirable low MUN breeding values.


CRV Ambreed’s Managing Director Angus Haslett says farmers are encouraged to start the journey to greener cows now as improved offspring will be born in 2018.


He says while there is a vast amount of research being conducted in New Zealand to mitigate nitrogen leaching, it makes sense to breed cows with lower MUN for economic and environmental reasons.


“We know farmers are doing everything they can to mitigate nitrogen leaching and meet environmental compliance levels. The beauty about the genetic approach is that it has an additive effect to other strategies a farmer might be taking to reduce nitrogen leaching. This CRV Ambreed announcement provides a long-term solution that fits within the standard AI mating programme,” Mr Haslett says.


He says genetics can produce great gains for farmers. “Farmers already choose CRV Ambreed bulls to breed certain traits in their cows so this is another step on that journey of finding solutions in genetics.”


CRV Ambreed is already known for its team of bulls that are helping breed higher tolerance to Facial Eczema and has also launched homozygous polled bulls, whose progeny do not require time-consuming and costly dis-budding.


But the MUN project is especially timely: CRV Ambreed says this research potentially provides a huge leap forward towards a more sustainable dairy industry by enabling farmers to breed towards environmental compliance.


Leave a Reply

Your email address will not be published. Required fields are marked *