Nitrate reducing forage plants and bacteria, denitrification walls and now nitrate-busting bulls are being developed to lower farming’s impact on the environment.
Thanks to an international breakthrough by dairy herd improvement company CRV Ambreed, bulls have been identified that pass lower nitrate levels through their urine onto soils.
The company has selected bulls genetically superior for a trait related to the concentration of urea nitrogen in milk.
A team of 25 bulls was identified with the genetic makeup for low concentration of milk urea nitrogen (MUN), including 10 each from jersey and friesian breeds and five kiwi cross sires.
In line with overseas studies, principal geneticist Philip Beatson has found bulls that will breed daughters with the desired low levels of MUN.
The breakthrough promises to reduce the amount of nitrates excreted in urine and therefore reduce its leaching on farms by 20 per cent within 20 years. This will result in a more sustainable dairy industry and take the heat off dairy farmers increasingly pressured to play their part in cleaning up waterways, says Beatson.
“If the connection between milk urea nitrogen and urine nitrogen carries over, 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.
The team of 25 bulls identified with lower MUN breeding values than average unselected bulls is being marketed this year as LowN Sires.
“What we are confident about is that the bulls we are releasing in the LowN sires brand will reduce the milk-urea nitrogen concentration in their progeny. Daughters of [the bulls] could save New Zealand 10 million kilograms in nitrogen leaching a year, based on the national herd number of 6.5 million dairy cattle,” Beatson says.
Selecting dairy sires with breeding values for lower MUN will produce progeny that excrete over three kilogrammes less nitrogen/cow/year in their urine, he says.
In one generation that reduction would equate to about an 8-10 per cent reduction in nitrogen leaching per hectare in the average dairy herd.
“We predict, with all other things staying the same, that genetics could lead to 20 per cent less leaching in 20 years – 20 per cent is a massive figure. This genetic approach will be added to other things a farmer may take to reduce nitrogen leaching,” Beatson says.
Since 2012, CRV Ambreed has measured MUN concentrations in 650,000 milk samples and analysed them to understand how strongly the trait is inherited to create a MUN breeding value for the cows measured as well as their sires.
“The genetics around MUN was done 10 years ago primarily to investigate whether lower MUN levels were linked to the higher efficiency of nitrogen use,” Beatson says.
“What is different is the way that we are thinking about MUN. Essentially we are asking whether, if we reduce MUN through genetics as opposed to diet as done in the nutrition studies, cows urinate less nitrogen and therefore nitrogen leaching is reduced.”
The leading cause of nitrates leached into the ground and waterways comes from cow’s urine concentrated in patches of pasture. Some of the nitrogen excreted is converted to gas, some is taken up by plants, and a substantial amount is leached into the soil.
LowN cattle are expected to excrete lower nitrate levels as urine compared with today’s average cows when considering them being fed the same diet,” Beatson says.
“If we feed another diet which increased average MUN levels then LowN cows would have a lower MUN and retain their advantage of lower urinary N and lower leaching.
Beatson said studies so far showed that selection for low MUN had not negatively affected other important genetic traits dairy farmers looked at when choosing semen, such as milk production, calving ease or fertility.
One outcome of the company’s work is a negative but favourable relationship between MUN and the percentage of protein in milk. Put another way, cattle with lower MUN have a higher percentage of protein. This indicates that LowN cattle are partitioning dietary nitrogen away from urinary nitrogen and into milk protein. This produces higher levels of protein in milk.
“This finding gives CRV Ambreed further confidence that cows bred for lower MUN do in fact partition their dietary nitrogen differently to the average cow. Breeding cows for low MUN will not only reduce the amount of nitrogen excreted in their urine but will also increase the efficiency with which dietary nitrogen is used for milk protein production,” Beatson says.
Farmers are now able to breed cows using straws of semen from LowN Sires, and their daughters will have reduced concentration of MUN.
Some of the top bulls in the country have the desirable genetics for MUN, which means farmers can still select bulls with all their required traits, with the bonus of low nitrogen leaching.
“We believe it would be irresponsible if we didn’t give farmers this opportunity now. The choice is theirs. We plan to do the science particularly to prove the MUN – urinary nitrogen link in genetically improved cattle, but that will take another four to seven years. By the time we do the work, those farmers who come on the LowN Sires journey with us will have herds potentially leaching 10-12 per cent less,” Beatson says.
CRV Ambreed engagement strategist Lynda Clark says the genetic discovery is an important one for sustainable farming and improving the quality of waterways as they were “hot topics.
“Farmers are using many management practices to reduce nitrogen loss, and LowN Sires is another powerful tool. It’s easy, no additional cost and simple solution to reducing nitrogen leaching on dairy farms.”
“I think we need to be able to put our hands on our hearts and say we are doing all we can to make a difference. There is increased pressure on councils to improve the quality of waterways and to be accountable. So part of my job is to raise awareness of LowN Sires and let them know more about this innovation, which has the potential to make a difference to farmers.
“It’s a powerful tool in a farmers toolbox and its something that can have an impact at no extra cost – it’s as easy as choosing this straw [of semen] over that straw.”
Source: Stuff
