Selecting dairy sires with breeding values for lower milk urea nitrogen concentration (MUN) will potentially produce progeny that excrete 3.2kg less nitrogen/cow/year in their urine.
That reduction in one generation would equate to about an 8-10% reduction in nitrogen leaching per hectare in the average New Zealand dairy herd, research and development manager Phil Beatson says.
“It’s potentially very exciting. If we reduce the amount of nitrogen being excreted, we reduce leaching.”
CRV Ambreed has developed a breeding value for sires for MUN, which is known to have a relationship with urine nitrogen output.
The relationship between MUN concentration and nitrogen in the urine has been researched overseas in trials where cows are fed different diets. These studies show that for a one-unit increase in MUN the increase in the amount of nitrogen excreted in urine a day is about 15grams. The graph in this article illustrates this relationship.
Genetic studies including those of CRV Ambreed have found MUN to have a heritability of 0.16-0.30.
“The genetics around MUN was done 10 years ago primarily to investigate whether lower MUN levels were linked to higher efficiency of nitrogen use.
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.
“We are confident that the sires we are marketing in 2017 will reduce MUN in their daughters.
‘We predict, with all other things staying the same, that genetics could lead to 20% less leaching in 20 years – 20% is a massive figure. This genetic approach is expected to be additive to other actions a farmer may take to reduce nitrogen leaching.’
“In essence what we are proposing is if we come down the line in the graph due to genetics, do we reduce urinary nitrogen?”
MUN is the nitrogen content of milk urea: MUN is 46% of the milk urea.
CRV has tested 650,000 milk samples for MUN concentration over the last five years, completed a genetic analysis and has estimated breeding values for the sires of those cows.
A team of 25 bulls has been identified with lower MUN breeding values than average unselected bulls and these will be marketed this year as LowN Sires.
“What we can guarantee with these bulls is that they will reduce the concentration of MUN in their progeny.
“We are confident that reducing MUN through genetics will reduce the nitrogen excreted in urine. There is no reason why it won’t, but it’s desirable to prove that,” Beatson says.
CRV is launching the LowN Sire team this year without that scientific proof of principle because the industry needs to act now to meet its environmental responsibilities.
“We believe it would be irresponsible if we didn’t give farmers this opportunity now. The choice is theirs. We could do the science to the nth degree but that will take another four to seven years. By the time we do the work, those farmers who come on the LowN journey with us will have herds potentially leaching 10-12% less.”
This year’s bull team has an average breeding value of -1.2 for MUN. The breeding values for all bulls including many that are now unavailable range from -2.6 to +2.4.
“We are aiming to produce better bulls for MUN each year. From our calculations it’s perfectly possible in eight years time for a herd to be -1 for MUN,” Beatson says.
The progeny from this year’s LowN sires compared to the progeny of the average bull will be -0.6 MUN units. The average NZ dairy cow has a MUN value of 14 MUN so the average progeny from a bull with MUN breeding value -1.2 would be 13.4 MUN units.
Several studies show a cow excretes 15g urine N/day for every unit of MUN. So if a cow has a reduced MUN level of 0.6 units that would mean a reduction of 9g/day of nitrogen excreted.
Over 360 days that equated to 3.2kg /cow/year less nitrogen in the urine.
Whole farm models predict that herds which excrete 3.2kg urinary nitrogen/cow/year less, will result in a reduction of 8-10% in nitrogen leached per year, Beatson says.
“We predict, with all other things staying the same, that genetics could lead to 20% less leaching in 20 years – 20% is a massive figure. This genetic approach is expected to be additive to other actions a farmer may take to reduce nitrogen leaching.”
Farmers who herd-tested with CRV Ambreed would be able to get a breeding value for their cows from July, which was another step on top of sire selection to breed a herd with a lower nitrogen leaching figure.
“That’s the second edge of the genetics sword – but sire selection is the most important.”
Some of the top bulls in the country have desirable genetics for MUN, which meant farmers could still select bulls with all their required traits, with the added bonus of low nitrogen leaching.
“The beauty of the genetics approach is that this has no impact on the farming system. Farmers can simply use a straw from a LowN bull rather than another straw and potentially they’re going to reduce leaching significantly.
“This is a powerful tool in the farmer’s tool box to mitigate environmental impact.”
The next stage of research is to prove animals that are genetically different for MUN do in fact excrete different amounts of nitrogen when fed the same diet. This involves bringing high-MUN and low-MUN animals to the same location and feeding them the same diets. Urine nitrogen and MUN will be measured to investigate the MUN-urine nitrogen relationship.
It is possible the phase-two research will investigate where dietary nitrogen is going if it’s not going into urine.
Cows will be studied in metabolism crates as part of the research to measure all of their nitrogen outputs, Beatson says.
More nitrogen going into milk, growth or dung would be a good outcome. Nitrogen contained in dung takes longer to break down which gives plants the ability to utilise it.
More nitrogen into gases would be less desirable, but in NZ’s situation it was still a positive result because of the intense focus on improving water quality.
“We can now identify animals that are genetically different for MUN and use those diverse animals to work out whether there are differences in the way they partition their dietary nitrogen.
“That creates world-first opportunities.”
Science provides answers
CRV Ambreed is in the business of improving farming systems and at the moment helping farmers to reduce their environmental impact is a significant focus, managing director Angus Haslett says.
It meant a lot to be able to give farmers a genetic tool to use in the environmental challenge that the industry is facing.
“It’s such a great story for our industry. Science has stepped up to provide an answer.
“This can really make a difference in our industry.”
Several hundreds of thousands of semen straws are available to meet the demand this year for its team of LowN bulls.
The team of 25 bulls across the three dairy breeds includes some top bulls including Superstition and Malestrom, CRV Ambreed sales and marketing manager Matt Macfie says.
“Our sales team is so excited to be able to bring this to customers, they are at the coal face seeing the challenges our farmers are facing. This is a great way to help farmers achieve their environmental goals.”
Farmers can expect to pay the normal rate for the LowN straws. There will be no premium for it, Macfie says.
The next step would be to work with key industry groups to create a national breeding value for MUN.