Environmental Efficiency More milk, less methane production

June 10, 2009 07:00 PM
 

If you don't think efficient milk production aids the environment, think again, says David Galligan, a professor of animal health economics with the University of Pennsylvania School of Veterinary Medicine.

Galligan has pulled together what he calls a "visual analytic” on his Web site that demonstrates the connection between dairy cow numbers, milk per cow and nutrient excretion. (Follow the link at DairyToday.com.) The analytic looks at these factors from 1950 through 2006.

In 1958, for example, U.S. dairy producers reportedly milked 18.8 million cows but produced just 6,585 lb. of milk per cow and 124 billion pounds of milk annually.

That amount of milk production resulted in 264 lb. of methane, 110 lb. of nitrogen and 48 lb. of phosphorus per cow. The total amount of methane produced from dairy cows in 1958 was 4.96 billion pounds. Nitrogen excretion was 2.1 billion pounds and phosphorus excretion was 902 million pounds.

So, for every pound of milk produced, 0.04 lb. of methane was also produced, along with 0.017 lb. of nitrogen and 0.007 lb. of phosphorus.

Fast-forward to 2006, when 9 million U.S. cows produced 19,576 lb. of milk per cow and 176 billion pounds of milk nationally. In other words, milk production per cow tripled during those fifty years while cow numbers fell 52% and total milk production climbed 40%.

During the same period, the amount of methane produced per cow jumped 25% to 330 lb., nitrogen excretion nearly doubled to 215 lb./cow and phosphorus jumped slightly, to 51 lb./cow.

On a total basis, however, methane production actually dropped 60% to 2.8 billion pounds. Nitrogen excretion dropped 6% to 1.9 billion pounds and phosphorus excretion dropped in half, to 459 million pounds.

Because of improvements in efficiency, methane output per pound of milk dropped 58% to 0.017 lb. Nitrogen excretion dropped by a third, to 0.01 lb., and phosphorus excretion dropped nearly two-thirds, to 0.0026 lb.

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