Grape by-product cuts dairy emissions by 20 per cent

Cow in feeding stall

At a glance

• Study at DPI Ellinbank found cows fed wine grape by-product decreased methane (CH4) emissions by 20 per cent.
• Grape marc also substantially increased healthy fatty acids in milk.
• 200,000 tonnes of wine grape by-product is produced in Australia every year, most of which goes to waste.

Feeding by-products from the wine making process to dairy cows can reduce methane emissions by 20 per cent, according to a new study.

Researchers fed cattle the stems, seeds and skins from wine grapes — known as grape marc — for just over a month and found that as well as slashing emissions the diet also improved the nutritional value of milk.

DPI scientist Peter Moate said this type of study had never been done before.

“This is the first experiment that I’m aware of in the world where people have fed grape marc to cattle and measured the methane response.”

The background

A cow consuming ensiled grape marc

Dr Moate said the experiment culminates a three-year project into reducing methane emissions from dairy cows.

Methane is a potent greenhouse gas, 21 times more powerful than carbon dioxide in terms of its global warming potential.

“We’ve been investigating nutritional ways to reduce methane emissions from dairy cows. To date we’ve examined a number of feed supplements, including whole cotton seeds. Feeding whole cottonseed can reduce methane emissions by about 15 per cent,” Dr Moate said.

From a review of the scientific literature worldwide, Dr Moate has calculated that each one per cent increase in dietary fat consumption delivers methane emission reductions of 3.5 per cent.

Therefore, an increase in the dietary fat concentration of four per cent can result in a 14 per cent reduction in methane emissions, particularly in summer months when the fat concentration in pastures is lower than at other times of the year.

Introducing grape marc

Ensiled grape marc up close

Currently, 200,000 tonnes of grape marc are produced in Australia each year, mostly along the Murray irrigation areas.

The bulk of it is ploughed into the soil although a small amount is being used in feedlots.

As well as its plentiful supply, Dr Moate said grape marc appealed as a potentially useful dietary methane mitigant because it has a high concentration of fat and also a high concentration of tannins, both of which are known to reduce methane production in cattle.

Most people are familiar with tannins. They are the chemicals in red wine that give it an astringent taste.

The study, carried out at DPI Ellinbank, saw 32 cattle divided into three groups and fed different diets over 37 days.

The first was a control group and each cow in this group was fed a diet containing crushed wheat grain and lucerne hay, while the second group was fed a diet containing crushed wheat grain, lucerne hay and 5kg of dry matter (DM) of pelleted dried grape marc.

The cows in the third group were fed the control diet and 5kg/DM of ensiled grape marc. The dietary composition of the ingredients are shown in Table 1.

The ensiled grape marc was stored in sealed plastic bags to prevent it from rotting.

The cattle were milked twice a day over the 37 day study period.

The results

Dr Moate said the results were amazing, with both groups fed grape marc achieving a 20 per cent reduction in methane emissions expressed in grams per day, with the same reduction in grams emitted per kilogram eaten (see Table 2).

And he said the benefits didn’t stop there.

“Grape marc contains a lot of unsaturated fatty acids, especially linoleic acid. By feeding grape marc to the cows we increased the concentration of unsaturated acid, polyunsaturated acid and reduced the concentrations of saturated acids in milk.” This is shown in Table 3.

Dr Moate said the grape marc also substantially increased the concentrations of conjugated linoleic acid in milk, a fatty acid known to combat cancer, diabetes and arthritis.

This experiment was conducted with cows in late lactation. Dr Moate hopes to repeat the trial with cows in early lactation.

Who benefits?

Dr Peter Moate with a cow involved in the study

As well as providing winemakers with a ready outlet for their waste product, Dr Moate said grape marc represented a cost effective way for neighbouring farmers to improve their milk quality and help the environment.

Those further afield may struggle, however, as ensiled grape marc is bulky and expensive to transport and there are some transportation restrictions on ensiled forms of grape marc to prevent the spread of the grape disease phylloxera.

The big picture

Previously, researchers had looked at black wattle for its tannins, which in overseas research was found to reduce methane emissions by 15 per cent.

While DPI researchers were able to replicate these results, the cows were less impressed.

“It’s very bitter and cows don’t like to eat it, so it had to be drenched,” Dr Moate explained.

Feeding cattle a combination of black wattle tannin and cotton-seed oil was expected to provide an added decrease in emissions, but this failed to happen.

Meanwhile, algae meal being grown by Australian power plants as a way of using their captured emissions was also trialled.

In the DPI study, however, no difference to emissions was achieved, although omega 3 levels in milk were enhanced.

Dr Moate said there was much scope to reduce emissions from cattle.

“I don’t think there will be a silver bullet that will reduce them completely. What we’re thinking is that there will be a number of approaches that when combined will substantially reduce emissions of methane,” he said.