Farming Magazine - August, 2009


Dairy Nutrition: The Nitrogen Footprint

By John S. Hibma

Many years ago in a college biology class, I recall the professor saying that in any bio-system enough waste will eventually be produced to destroy the life in that system. From the bacteria growing in a laboratory culture dish to the Earth itself, the waste products generated by all living organisms will eventually overwhelm the organisms’ environment and their ability to survive. In the case of a petri dish it may take only weeks; in the case of our planet it will take many millennia.

While I was still in high school in 1969, the Cuyahoga River in Cleveland, Ohio, caught fire, drawing some of the first serious national attention to the extent that mankind was irresponsibly polluting the world around him. Forty years later, with an exponentially larger population and a greater awareness of how fragile our world is, we have, perhaps, won a few of the “smaller battles,” resulting in cleaner rivers, and we’ve managed to slow some aspects of pollution. But, in reality, we’re losing the “war against pollution” as we continue to poison our world.

Carbon and the associated reduction of CO2 emissions has inadvertently garnered about 99 percent of the media’s recent attention as the most imminent and primary threat to the human race’s survival on the planet. Lying just under the radar these days is nitrogen, the other “most important building block of life.” While it appears that anyone who drives a car, flies in an airplane or heats their home gets to share the blame over our carbon footprint, it will be agriculture, agribusiness and the poor farmer who are going to shoulder the responsibility of managing the nitrogen footprint after Al Gore writes a book about it.

Dairy farmers, beware!

If you’re not already aware of it, you’re standing right in the path of the nutrient management regulatory steamroller that’s mandated to control nitrogen pollution. Whether you like it or not—even if you’re milking only a few cows—eventually you’re going to have to keep track of and manage how much nitrogen comes onto your property and how much leaves.

Nitrogen is an essential element for all living organisms—plants and animals—and is found mostly in the amino acids that make up proteins and peptides. In order for any plant and animal to grow and propagate, nitrogen must be present in the soil or growth medium. The proteins found in feedstuffs are converted to different proteins that are then utilized by animals. All dairy cow, heifer and calf diets must contain protein.

Nitrogen exists primarily in an inactive form in nature. It makes up almost 80 percent of the air we breathe. Before it can be used by animals it must combine with oxygen or hydrogen and become part of a protein complex in plants. Unfortunately, metabolization of protein in animal diets is not very efficient, and a great deal of reactive nitrogen is excreted in urine and feces as nitrates and ammonia. Therein lies the potential for too much nitrogen finding its way into the environment.

Attempting to balance dairy cow diets for the most efficient use of nitrogen is complicated by a number of things. First, the protein in forages is highly variable, making it difficult to keep dietary protein at proper levels. Milk production varies over the course of a lactation, making the balancing of protein a moving target and often resulting in its overfeeding. Finally, on-farm herd management is often counter-productive in minimizing excessive nitrogen releases into the environment.

What makes dairy cow nutrition so complicated is the fact that the rumen also has a protein requirement that is still poorly understood. It has taken researchers many years to determine a cow’s protein requirement as it relates to the rumen. Crude protein (CP) has long been the measure by which protein has been supplied in a diet, with little understanding of how individual amino acids (AA) are involved. Only in the last decade has our industry begun to recognize that dairy cow diets should be balanced according to AA levels and rates of protein degradation (RDP and RUP) in the rumen. Paying proper attention to those AA and RDP/RUP levels, rather than just CP, diets can actually be balanced with lower total nitrogen levels that will often support even more milk production or heifer growth rates.

Many things happen in the rumen that make it difficult to know which AAs are being degraded or being allowed to escape to the lower gut. We now have commercially prepared rumen-protected methionine and lysine products that enable nutritionists to balance diets for lower CP levels. While the use of these products only touches the surface of protein and nitrogen efficiencies in ruminant diets, it’s a good start in the right direction.

Over the years, milk cow diets have routinely been balanced for CP levels of 19 percent to 20 percent or more in an effort to support high milk production. Reducing a milk cow diet from 19 percent CP to 17 percent CP with the aid of rumen-protected AA can reduce nitrogen loss into the environment by about 70 grams per cow per day for a high-producing milk cow. That amounts to well over 2 tons of nitrogen per year for a 100-cow herd.

As both water quality and riparian habitat continue to become a valuable commodity, nutrient management plans, of which nitrogen is the largest component, will eventually be required in all regions of the country with dairy farms. While commercial fertilizer application still receives the most attention when it comes to the nitrogen footprint, the focus on dairy farming will continue to increase.

Work with your nutritionist or feed company professional to reformulate feed rations that effectively reduce the nitrogen output on your dairy. For larger herds, grouping your cows by production allows you to focus protein needs more accurately while not overfeeding cows with lower milk production. Dairy farms that are close to major waterways will receive greater scrutiny than those that are not. If our industry works proactively to manage its nitrogen footprint, it will be regarded in a positive light and as an important and necessary component of our food system rather than a contributor to the planet’s pollution.

The author is a dairy nutritional consultant and works for Central Connecticut Farmer’s Cooperative in Manchester, Conn.