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(Â鶹ÒùÔº) —The carbon hoofprint of dairy cows may be smaller than previously thought, report Cornell researchers.

Cows and other ruminants are the ultimate recyclers, and they deserve some credit for helping the environment while providing high-quality nutrients through their dairy products, says Michael Van Amburgh, professor of animal science.

Addressing a Sept. 12 food policy symposium hosted by International Programs in the College of Agriculture and Life Sciences, Van Amburgh explained that cows are often fed byproducts from human food and biofuel production processes that would be costly to dispose of otherwise.

In fact, the alternative – incineration – directly contributes to environmental degradation, so cows actually help reduce the impact of the human food supply and make that food supply affordable.

An example, he said, is the California almond industry that relies on cattle to consume four billion pounds of shelled almond hulls each year.

In addition, cows make use of land not suitable for food crops. And thanks to complex modeling – some of which was developed at Cornell – dairy farmers can precisely calculate the carbon output of their cows and adjust their diets accordingly.

"We can't change the cow's methane production by much, but we can change efficiencies, milk per unit of gas," Van Amburgh said.

Animal products provide an important source of nutrients, especially for children and older adults, that should not be discounted, he said. Even if we switch to a more plant-based diet, we would need an environmentally sound system of disposal for matter not consumed.

Van Amburgh pointed out that every food has an environmental impact, and that we should consider how many nutrients we get in return for the greenhouse gas emissions generated in its production.

For example, a 2010 Swedish study calculated the nutrient density – the nutrient content and number of nutrients per serving – of several beverages in relation to the greenhouse gas emissions associated with their production, manufacturing, packaging and transportation. Milk rated very highly, with a high nutrient density index per equivalent carbon emission of 53.8 per 99 grams greenhouse gas emission. Soy drinks and red wine, by comparison, have a nutrient density index of 7.6 per 30 grams and 1.2 per 204 grams of emissions, respectively.

Van Amburgh has also found in a study (not yet published) that carbon dioxide and methane emissions from byproducts included in animal feed are considerably lower when fed to dairy cattle than when incinerated.

Byproducts most often used in the American dairy industry include distillers' grains from ethanol production, citrus pulp from juice production, almond and soybean hulls, soybean meal, cottonseed, extracted canola meal and even baked goods and candy.

Their inclusion in animal feed not only helps the environment, but can boost nutrients and enhance yield and provide an economic opportunity for the byproducts that in many cases greatly reduces the cost of food to the consumer, Van Amburgh said.

"Because of the microbial fermentation digestion process that occurs in the cow's rumen, the byproducts are digested in a manner that can positively enhance the nutrient supply," he said. "For example, candy byproduct provides sugar and the end product of the fermentation produces the substrate necessary for milk sugar production, so fed in moderation, candy can enhance milk yield with no ill effects on the milk composition or quality."