Cattle emit less methane in the winter than in summer, a recent study has discovered.
And now that the results have been sent to the Intergovernmental Panel on Climate Change, scientists will use it to develop a more accurate picture of the true contribution of ruminants to global warming.
Previously, the IPCC had not taken into account the fact that rumen volume in cattle shrinks during cold weather, and as a result, Canadian cattle were unfairly lumped in with their counterparts in warmer climes, said Jennilee Bernier, who researched the issue during her time as a master’s student at the University of Manitoba and gave an overview of her results at the recent Manitoba Zero-Tillage Research Association’s annual general meeting.
“It’s misleading for countries like Canada or even Russia and other countries around the world that do have their cattle outdoors in cold environments, because our cattle in a year will produce less methane than currently predicted,” said Bernier, who comes from a ranching family in Fisher Branch and is now a MAFRI forage and beef specialist.
The study, the first of its kind, found that cattle emit 27 per cent less methane in the winter months for a number of reasons.
First, the process of cold acclimatization under an extended period causes physiological changes, including faster rates of rumen contraction.
This speeds up the passage of feed through the digestive tract, and reduces the time available for “methanogens,” the tiny bacteria that live in the rumen, to break down dry matter compounds into methane.
The study also looked at whether feeding DDGS as a protein supplement for cows consuming low-quality forages would increase daily dry matter intake and increase the efficiency of rumen fermentation, thus reducing methane emissions from the gut. Protein contains nitrogen, which acts as fuel for microflora.
Feed intake for the 30 mature open cows used in the study was measured with the computerized GrowSafe system of plastic feed bunks that automatically monitor individual consumption.
Methane emissions were captured and measured with vacuum suction canisters attached to each cow’s halter in an outdoor feedlot at the Glenlea Research Centre near Winnipeg.
The cattle were split into groups of 10, with all of them fed a base diet of poor- quality grass hay and straw. Onethird was fed just hay and straw for a six per cent crude protein diet, another third fed 10 per cent DDGS for a total of 8.7 per cent CP, and the rest 20 per cent DDGS for 11.5 per cent CP.
Temperatures in the fall of 2008 averaged 7 C, and -18 C during the winter months of 2009, within a total fluctuation range of 50.
Catheters captured every drop of urine during a 24-hour period, and manure was also weighed and collected for analysis. The cattle produced 1.3 litres less urine per day in winter than in fall.
The results showed a number of surprises. First, supplementing DDGS in the diet showed a slight increase in dry matter intake, but not enough to be statistically significant, said Bernier.
“Between seasons, I expected that in the cold with those faster rumen contractions that the cows would need to consume more feed, but we actually saw that it was pretty much identical between seasons,” she said.
“Those cows were full. They couldn’t eat more in the winter even if they wanted to.”
The cows fed 10 per cent DDGS produced the same amount of methane as the group fed just hay and straw, but the higher DDGS inclusion rate at 20 per cent resulted in “significantly less.”
But cold weather, rather than diet, had the greatest effect on methane emissions.
“This reduction is purely from being in cold temperatures. It has nothing to do with diet or protein,” she said.
Bernier speculated on the reasons.
In winter, fibre flow-through speed in the rumen is unchanged, but in the hindgut, it passes through 47.7 per cent faster. One clue to the cause of the reduced emissions is that fluid content of the rumen moves through 26.6 per cent faster in winter than in fall.
“With the rumen micro-organisms being washed through at a faster rate, they have less time to spend in the rumen, less opportunity to ferment fibre, and less chance to produce methane emissions,” said Bernier.
“It shows that the Canadian beef herd may produce less methane than previously predicted, and it may be at an advantage in terms of environmental sustainability.” daniel. [email protected]
– JENNILEE BERNIER