CRV Ambreed Low N Dairy Sires
The development of a genetic tool to reduce nitrogen leaching by dairy cows
Nitrogen leached from grazed pasture into waterways is a big issue in New Zealand, with urine excreted by cows the main source. The Parliamentary Commissioner for the Environment published a report in 2016, estimating that 43 per cent of New Zealand’s greenhouse gases are caused by methane (generated by all livestock) and 11 per cent by nitrous oxide (mainly by cows urinating).
In March 2017 an OECD environmental review team called for agriculture to be brought inside the New Zealand Emissions Trading Scheme. The following month, the Ministry for the Environment and the Department of Statistics released Our Fresh Water 2017, noting that nitrogen leaching from agricultural soils increased by an estimated 29 per cent between 1990 and 2012.
Nitrogen consumed as protein in feed by cows is directed into five areas; milk protein (plus urea), growth (muscle), dung, gases and urine. Milk Urea Nitrogen (MUN) results from the breakdown of dietary protein in the rumen, which releases ammonia. This ammonia is absorbed into the bloodstream and converted to urea in the liver. Urea is dispersed among body fluids such as milk, blood plasma and urine. Due to the large amount of crude protein (20-25%) in good quality pasture, MUN levels in New Zealand pastoral grazing systems are usually higher than in systems where cows are fed a mixed ration.
Dairy herd improvement company CRV Ambreed has made a genetic discovery that the company believes could reduce nitrogen leaching on New Zealand farms by 20% within 20 years. The company is selling semen from over 20 LowN Sires™ selected to be carrying a trait determining Milk Urea Nitrogen concentration (MUN) in milk. Daughters of 2017 LowN Sires™ will have lower MUN and are expected to excrete less nitrogen in urine than cows which have not inherited this trait. The company predicts these sires will breed cattle that could reduce nitrogen leaching by 20 per cent within 20 years.
The release of Breeding Values for Milk Urea Nitrogen (MUN) in March 2017 is thought to be a world first. Five years of research has shown that low MUN levels are heritable and likely to indicate low levels of nitrogen in urea. Concentrations in 650,000 milk samples have been analysed, to help understand this heritability.
“It’s what’s been getting me out of bed for the last four years,” says CRV Ambreed research and development manager, Phil Beatson. “At the start we were unsure of what we’d find, but as we’ve gone on, the results have become more and more compelling.”
Phil recalls the project was kicked off by a group of scientists over a cup of coffee at DairyNZ five years ago, chatting about environmental issues which animal geneticists might be able to help with. European scientists seeking to improve feed efficiency had already discovered a correlation between the concentration of Milk Urea Nitrogen and nitrates in cows’ urine, when fed different diets.
The seasoned scientist counts the breakthrough as the second highlight of a career that has spanned over 45 years. (The first was in the mid-1980s, when he was involved in developing breeding programs for lean but heavy lambs.) He is optimistic the MUN finding will be equally if not more significant in reducing the New Zealand dairy industry’s part in deteriorating water quality.
“Daughters of these first sires will be born in 2018 and have their first lactation in 2020,” says Phil. “They could save New Zealand 10 million kilograms of nitrogen leaching a year, based on the national herd number of 6.5 million dairy cattle." Each of these cows is expected to excrete about 9 grams less nitrogen per day, adding up to a 3kg annual reduction.
Many farmers were already making significant changes (such as manipulating feeds) to management to reduce their environmental footprint, Mr Beatson said. Selecting for this trait will be an additional tool to reduce nitrate leaching, as pressure continues to increase to clean up waterways.
Phase one of the New Zealand study is now complete, confirming that bulls with a desirably low EBV score will reliably pass this on. A second stage is underway, aimed at confirming that low-MUN cows will excrete less nitrogen in their urine than high-MUN cows. High and low animals will be included in intensive trials to measure dietary intake and excretion of nitrogen. The proposed seven-year project is being led by DairyNZ helped by AgResearch, Fonterra, CRV Ambreed and Lincoln University.
Work is also planned on MUN-associated traits, including efficiency in the uptake of nitrogen, linked with productivity and efficiency. No obvious negatives have been discovered.
Phil anticipates the day when the low MUN trait will earn credits in nitrogen measurement and management schemes like Overseer. This will be critical as pressure increases for farming to be brought inside New Zealand’s Emissions Trading Scheme.
Double benefits were likely, as farmers should eventually be able to breed LowN™ cows along with adopting other nitrate-reducing strategies such as selecting feeds which reduced urea in urea in both milk and urine.
Farmers already subscribed to CRV Ambreed’s herd-testing and recording services will automatically receive MUN values for their cows by the end of 2017.
“We are saying to farmers, consider getting on board now because breeding for this trait could make a big difference. Over generations, benefits will accrue so long as the relationship between MUN and urine nitrogen holds up.”