With all the hubbub over dairy cows' contribution to greenhouse gases, one fact is often forgotten.
Today's U.S. dairy herd emits 30% less methane while producing twice as much milk with 57% fewer cows than our great-grandparents' herds did in 1924. In the end, each gallon of milk produced today results in just a third of the methane emitted for milk produced back in 1924.
Alvaro Garcia, dairy nutritionist with South Dakota State University, and Jim Linn, dairy nutritionist with the University of Minnesota, selected 1924 as their basis for comparison since that was the year national estimates of cow numbers and milk production became available.
In 1924, more than 21.4 million cows were being milked, but they only produced just a little more than 4,000 lb./cow/year. In 2007, the U.S. dairy herd numbered 9.15 million cows, with average production exceeding 20,000 lb./cow/year. Garcia and Linn estimate that a 1924 herd emitted 237.7 terajoules of methane compared with 169.3 terajoules today.
"Efficiency is key,” Garcia says. "Anything we can do to increase the utilization of feed to produce more milk will reduce greenhouse gases.”