Productivity Cuts Cow numbers, Total Methane

More productive dairy herds

– requiring fewer cows to produce more milk

– have resulted in less overall methane emissions into the atmosphere, according to a new South Dakota State University study.

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.

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

Garcia and Linn compared today’s dairy herds to those of 1924, the first year USDA dairy statistics were compiled. Modern dairy cows weigh more than those of 1924 as a result of genetic selection and a reduced number of mixed breeds, and therefore generate more methane per animal. However, in 2007, there were 9.15 million cows producing an average of 20,231 lbs. of milk per cow annually. In 1924, there were 21.42 million cows with a yearly per-cow average of 4,162 lbs. of milk.

“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% grain and 50% forage.”

Dairy cow methane production is associated with total feed intake – the more a cow eats, the more gas she will produce. Average cow feed intake 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 lbs. of milk, with a feed intake of 21.3 lbs. of dry feed. Cows produced just under 0.5 lb. of methane daily. In comparison, 2007 dairy cows produced on average five times more milk – 55.4 lbs. per day – and consumed on average 41.6 lbs. of dry feed. The dairy cow of 2007 produced almost 0.75 lb. 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% 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, Garcia concluded.