A study by USDA scientists finds that raising cows on grass, instead of in factory farms, produces fewer greenhouse-gas emissions and other pollutants.
by Marian Burros
Buy milk that comes from grassfed cows to support a system that reduces greenhouse gases and produces better-quality milk.
C. Alan Rotz, PhD, an agricultural engineer for the USDA’s Agricultural Research Service at University Park, Pennsylvania, and an adjunct professor at Penn State, was the lead researcher for the dairy cows study. And he says he is “tired of all the criticism” about cows raised on pasture. “There’s a place for grass-fed cows. There’s nothing wrong with grass-based systems, and from an environmental point of view there are a lot of benefits,” he says.
According to the USDA’s Agricultural Research magazine for May/June 2011, Rotz’s peer-reviewed study, first published in a research journal in 2009, concludes that “a dairy cow living year-round in the great outdoors may leave a markedly smaller ecological hoofprint than her more sheltered sisters.”
To find out which system was best from a sustainable point of view, the researchers compared four methods of milk production: two with confined cattle, one producing 22,000 pounds of milk a year, another, 18,500 pounds, and a third in which the cows were on pasture for seven months a year, each cow producing 18,500 pounds of milk a year. The fourth group of cows was fed on pasture all year long, and produced almost 9,000 pounds less milk.
The study looked at the environmental problems each group of cows produced: ammonia emissions from manure, soil denitrification rates, nitrate leaching losses, soil erosion, and phosphorous losses from field runoff. Estimates for emission of carbon dioxide, methane, and nitrous oxide were also taken.
Total emissions for greenhouse gases were 8 percent lower in the year-round outdoor systems than in either of the confined systems. Ammonia emissions were reduced by 30 percent.
Keeping cows outdoors reduced fuel use, as well as the carbon dioxide emissions from farm equipment. And one very important point: “When farmland is transitioned from rotated crops to perennial grassland, you can build up lots of carbon in the soil and substantially reduce your carbon footprint for 20 to 30 years,” said Rotz.
Raising cows in pasture is also good for water quality because of a huge drop in sediment erosion. The runoff of phosphorous also drops significantly.
Grass-fed cows aren’t as efficient in producing milk, at least in terms of volume. Each confined cow produces 22,000 pounds of milk a year, while the pasture-raised cow produces only 13,000 pounds. However, the total amount of milk protein and fat in the milk produced was essentially the same, because “the foraging cows produced milk with far more fat and protein,” explains Rotz. Even more important in the argument, Rotz says, is that 130 grass-fed cows can produce the same amount of milk as 80 confined cows on the same amount of land. That’s because amount of land needed to raise feed (grain) for the 80 confined cows is the same as the amount of land needed for grazing 130 cows.
The study did not address the composition of the milk. Milk from grass-fed animals has much more of a type of unsaturated fat, called conjugated linoleic acid (CLA). Evidence is increasing that CLA can protect the heart. Milk from grass-fed cows also produces more omega-3 fatty acids (the reason people tell you to eat a lot of salmon) than that from cows fed grains.