Saturday, April 20, 2024

Research producing cleaner cows

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Two separate pieces of research could help farmers breed more environmentally friendly dairy cows that excrete less nitrogen and methane. The first, at Lincoln University, shows cows with low milk urea nitrogen breeding values (MUNBV) produce less nitrogen in urine.
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The second, by dairy improvement companies LIC and CRV Ambreed, will determine if the methane produced by cows and their genetics are linked.

Research by Lincoln doctoral student Cameron Marshall shows dairy cows with low MUNBV have 28% less urinary urea nitrogen loading per urine patch than cows with higher MUNBV.

The lowest MUNBV animals in the study excreted 165.5g less urinary urea nitrogen a day than the highest MUNBV animals.

Lincoln livestock production experet Professor Pablo Gregorini said the findings are very significant for farmers and the entire agriculture sector.

“Cameron’s work shows that the cows themselves are an important tool in helping to cut nitrate leaching and nitrous oxide emissions and in helping farmers meet their regulatory reductions.”

To to do that while increasing milk protein is a huge win-win for the sector, he said.

“Most farmers’ herds will naturally comprise a mixture of low MUNBV cows and higher MUNBV cows with the trait being identified through testing the milk. 

“Simply identifying the animals with low MUNBV will enable famers to breed from their existing stock and change the make-up of their herd over time.”

Typically, 25-30% of the protein eaten by cows on a pasture diet is converted to milk. The rest is excreted as concentrated nitrogen in urine.

The research looked at whether there is a relationship between animals with MUNBV and what the animals urinate.

Cows from Lincoln University Dairy Farm’s herd were taken and split into two groups based on their MUNBV.

One group grazed a ryegrass/clover mix and the second, a ryegrass/clover/plantain mix. The cows did two grazings in May and November-December of the 2018-19 milking season equipped with urine sensors to measure the nitrogen excreted and recorders to measure grazing frequency.

“If you compare the lowest urea nitrogen cow and the highest, the lowest excretes 163.5g less of urinary urea nitrogen compared to the highest.

“If you assume that cows in general excrete between 300-400g of nitrogen a day this is 30-40% of the nitrogen excreted as urea in the urine – a massive reduction,” Gregorini said.

The low nitrogeno-emitting cows were typical-looking Kiwicross dairy cows. The cow that had the lowest MUNBV was also the most efficient producer of milksolids and higher protein levels.


The research will now look at how the nitrogen excretion levels react to supplementary feeds including 100% plantain.

“These are parts of the tools farmers can use. This is no silver bullet but it is an important tool.

“We are now able to look at the animal as a solution rather than a problem,” he said.

In Waikato LIC and CRV are investigating the possible link between the methane cows produce and their genetics.

Stage one of the trial involves measuring the methane a small number of bulls produce. Once the systems have been fully tested a full trial will get begin in February to identify individual bulls that produce less methane and potentially breed a lower-methane-emitting cow.

LIC chief scientist Richard Spelman said research in other ruminating animals such as sheep identified genetic variation for methane production.

“We’re undertaking research to see if there are similar results in NZ dairy cattle.

“If we’re successful and establish that the variability of methane emissions between NZ dairy bulls can be linked back to their genetics the opportunity is to utilise this variability to breed cows from lower methane-emitting bulls.

“This type of science doesn’t happen overnight but we have real potential to help farmers meet the 2050 methane target under the Climate Change Response Act.”

The daily feed intake and methane output of 12 young bulls is being closely monitored at LIC’s Chudleigh Farm with another seven being assessed under similar conditions by CRV.

LIC’s bulls are in a purpose-built barn and fed lucerne hay cubes imported from Australia in feed bins that measure how much each bull eats. 

The bulls are enticed to visit a methane measuring device, called a Greenfeed, using a small feed of pellets to keep them in the machine for three to five minutes.

Methane is measured each time the bulls visit the Greenfeed machine giving about three readings an animal a day.

If the trial is successful the same method will be used on about 300 bulls in a full trial scheduled for February.

“By 2023 we also hope to validate the methane measurements we captured in young bulls during the initial trial stages were representative of the methane output in lactating cows,” Spelman said.

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