A History of Methane Emissions

US - Modern dairy cows produce more methane than their predecessors, but fewer dairy herds and a smaller dairy cow population has resulted in less overall methane emission.
calendar icon 11 July 2008
clock icon 3 minute read

South Dakota State University Extension Dairy Specialist Alvaro Garcia, along with James Linn, head of the University of Minnesota Department of Animal Science, looked at the role cattle and dairy cows play in methane emission.

Garcia and Linn presented their findings at the 2008 American Dairy Science Association meeting in Indianapolis.

They compared today's dairy herds to those of 1924, the first year U.S. Department of Agriculture cattle and dairy statistics were compiled.

"In 1924, more than half of U.S. dairies grazed their cows nearly six months of the year with diets that consisted almost exclusively of supplemental forages"
South Dakota State University Extension Dairy Specialist Alvaro Garcia

According to the Environmental Protection Agency, agriculture is responsible for roughly 30 percent of the total methane emissions in the United States. A majority comes from gastro-intestinal fermentation and manure management.

Modern dairy cows weigh more than those of 1924 as a result of genetic selection and a reduced number of mixed breeds.

In 2007, there were 9.15 million cows producing on average 20,231 pounds of milk per cow yearly. In 1924, there were 21.42 million cows with a yearly per-cow average of 4,162 pounds of milk.

Garcia said other comparisons were also striking.

"There were also drastic differences in the production systems. In 1924, more than half of U.S. dairies grazed their cows nearly six months of the year with diets that consisted almost exclusively of supplemental forages," Garcia said. "The majority of today's dairy operations confine their animals and feed a diet of roughly 50 percent grain and 50 percent forage."

Dairy cow methane production is associated with total feed intake, thus the more a cow eats, the more gas she will produce. The average feed intake of dairy cows is determined by their production, and their genetic drive to produce more milk stimulates them to eat more feed.

In 1924, the average daily production was 11.4 pounds with a feed intake of 21.3 pounds of dry feed. Cows produced just under one-half pound of methane daily.

In comparison, 2007 dairy cows produced on average five times more milk - 55.4 pounds per day - and consumed on average 41.6 pounds of dry feed. The dairy cow of 2007 produced almost three-quarters of a pound of methane per day.

Although the results show modern cows produce more methane daily, in 1924 there were 12.3 million more dairy cows in the United States.

"This large number of cows resulted in 40 percent more total methane emissions when compared to 2007," said Garcia. "If we look at the ratio, three times more methane was produced per pound of milk in 1924 compared to 2007."

This research also showed that production efficiency started to change drastically during the mid-1950s, with fewer cows needed to produce more milk.

These changes resulted in less total methane production in spite of the increased gas production on a per-cow basis. Garcia said there are opportunities to reduce methane emissions from dairy cows.

"Feeding grains and their byproducts will continue to be a important practices to reduce methane emissions," he said. "Regrettably, high grain prices might challenge our ability to economically feed cows for reduced methane emissions. We must stress the importance of high quality forages to increase the efficiency of feed utilization and thus reduce the emission of methane."

Similarly, the use of production enhancers such as ionophores and growth hormone result in improvements in efficiency.

All these measures should be accompanied by an adequate ration balance according to the nutrient requirements of the different physiological states of the cow.

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