April 6, 2010

Greenhouse Gas & Dairy

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Using recycled paper and carpooling represent ways to decrease environmental impact. “Carbon footprints” quantify environmental impacts. However, a much more potent fuel for global warming, methane gas, frequently remains overlooked.

A Dec. 2009 article, “Livestock and Climate Change” by Robert Goodland and Jeff Anhang, reported that, “37 percent of human-induced methane comes from livestock.”

Methane’s global warming potential (GWP) is 25 times greater than the GWP of carbon dioxide on a hundred year basis. The article argues that global efforts should consider methane because a greater opportunity exists to reduce methane levels. Farmers may reduce methane levels by managing the diet of livestock.

Livestock primarily include “ruminants,” like cows, goats and sheep. The key characteristic of ruminants is the “rumen,” a specialized segment of the animal’s stomach that accommodates a community of microbes. These microbes form a symbiotic relationship with the cow.

Feeding the Dairy Herd describes two categories of carbohydrate digesting microbes that live in the rumen. The starch-digesting microbes tend to live shorter spans and produce higher levels of propionic acid.

The cow’s metabolic pathways convert propionic acid into glucose and lactose. Lactose, the sugar found in milk, drives the volume of milk output.

The other type includes fiber-digesting microbes. They live for longer intervals, and produce mostly acetic acid. Metabolic pathways convert acetate to milk fat. According to Prof. Larry Chase, animal science, this type of fermentation also results in methane production.

Various feeds contain different fractions of fiber with differing levels of digestibility. The digestibility of various forms of feed both depends upon the component fibers and the maturity of the plant at harvest.

Generally, farmers utilize two types of feeds. “Roughages” contain straws, hays and “silages,” which are fermented grass or legume crops. “Concentrates” contain grain, molasses or soy bean meal, and consequently, they are highly dense in energy and protein. Concentrates often provide supplemental nutrients that the roughage ration may lack.

Methane production is influenced by the type of digestion that occurs. By maximizing the quality of forage in a ration, farmers can decrease methane emissions.

As Chase explained, “You usually get more methane per unit of forage than you do per unit of corn. High quality forage gives you less methane than low quality forage.”

The U.S. dairy industry introduced “greener” milk. According to Chase, “The amount of methane produced by dairy cows now versus 1944 is about half in total.”

However, according to Chase, the amount of methane produced per cow has actually increased. A decrease in the cumulative size of the US herd and an increase in milk production per head caused this trend.

“In 1944,” Chase said, “the average cow produced something like 4,000-5,000 lb per year. Today, she produces somewhere around 20,000 per year.”

In the class, “Dairy Cattle Nutrition,” Chase teaches practices that maximize forage quality and increase feed efficiency. For instance, one type of mower, known as a “wide swath mower,” dries hay crops faster and more efficiently than previous mowers. The mower spreads the cut grass in a wider swath, allowing it to dry faster. Consequently, this limits the loss of sugar from the crop via cellular respiration, resulting in more digestible feed.

In addition, farmers may apply food additives. For instance, Rumensin is an antibiotic that improves feed efficiency. It inhibits fiber-digesting bacteria activity, allowing starch-digesting bacteria to populate the rumen. In the absence of fiber-digesting bacteria, these starch-digesting microbes rapidly ferment carbohydrates and produce more microbial protein. Consequently, they produce more propionic acid, increasing milk yields and decreasing methane production.

Confined Animal Feeding Operations (CAFO’s) represent some of the nation’s biggest recyclers. They utilize many byproducts of human food manufacturing in dairy cow rations.

Chase stated that, “The dairy industry and beef [industry] use a lot of byproduct feeds that are a result of processing food for human consumption.”

Original Author: Zachary Mason