SDSU research shows an overall methane emissions reduction on dairy farms

Using fewer cows that produce more milk than their historic predecessors, the modern dairy in South Dakota produces less methane despite a greater per-cow emission of the gas.

That’s according to Alvaro Garcia, a South Dakota State University dairy science researcher.

Garcia compared information from 2008 to the USDA records of 1933, and he found that today’s practices in dairy herds lead to an overall improvement in use of resources and a reduction in methane impact on the environment. He chose information from 1933 because it was then that the state saw its largest number of dairy cows.

“In 2008 South Dakota had 90,000 head of dairy cows, and each cow produced 19,956 pounds of milk, for a total of almost 1.8 billion pounds,” Garcia said. “In 1933, South Dakota had the highest number of dairy cows on record, 600,000 head, and combined, they produced a total of 2.1 billion pounds of milk.”

According to publications of the time, cows used to weigh around 1,000 pounds, but genetic improvements since then have allowed for greater milk production and larger cows that weight about 1,400 pounds

“They now eat more feed, and excrete more manure, and the dairy cow diets of the past also differed,” Garcia said. “Dairy diets consisted mostly of forages with very little grain supplementation. Cows nowadays have high grain diets, which oftentimes constitute 50 percent of their total feed intake, the rest comprised of highly digestible forages.”

Garcia and James G. Linn from the University of Minnesota presented research at the National American Dairy Association meetings last year that determined cows ate around 22 pounds of feed dry matter in 1933.

“Nowadays they consume close to 50 pounds of feed dry matter, and this is important because research shows methane production can be estimated from feed intake,” Garcia said. “Simply put, the more cows eat the more methane they produce, and as a result, cows of 1933 produced half the methane of today’s cows.”

Garcia said that the key idea to these findings was that there were 6.6 times more cows in the state in 1933 than there were in 2008.

“The overall methane contribution to the atmosphere and the methane emissions per pound of milk produced both were three times as high in 1933,” Garcia said. “Manure excretion followed a similar trend. The diet of 1933 was estimated to be 60 percent digestible, where today’s diet is close to 65 percent.”

Garcia said this means that the cows that ate 22 pounds of dry feed would have excreted nine pounds of dry weight manure and urine. Today, cows eat 50 pounds of a ration dry matter and excrete close to 18 pounds of dry waste.

“Although there was almost twice as much excretion on a per-cow basis during 2008, the total excretion amounted to 296,000 tons of dry manure,” said Garcia. “In 1933, cows produced 964,000 tons of dry manure.”

Garcia said this shows that improved dairy management practices have allowed South Dakota dairy producers to use natural resources more efficiently, allowing a reduction in cow numbers by nearly six-fold.

“Future advances in technology are expected to further improve the efficiency with which dairy cattle convert forages into dairy products in environmentally friendly systems,” Garcia said.
 

For more information, visit the South Dakota Cooperative Extension Service dairy Web site at this link: http://dairysci.sdstate.edu/extension/extension.htm.