Balancing Animal Rations for Nutrient Management

by Victoria Mundy, Extension Educator

For once, it might be possible to please everyone. Good animal production and environmental protection can both be achieved with ration balancing for nutrient management.

When an animal of any species takes in nitrogen (N) and phosphorus (P), only a portion of the nutrients is used within the animal's body for growth and maintenance. Some N and P go into milk, wool, or other products.

Much N and P ends up in manure. Sometimes crop fields can become overloaded with N and P when large amounts of manure are applied to land.

Fortunately, you can control the amount of N and P that animals excrete by balancing their rations. And in many cases, rations that precisely meet animal requirements for production will also minimize N and P excretion. In other words, it is not necessary to trade production for the sake of reducing N and P in the environment!

There are two major strategies for reducing N and P excretion: To help animals use N and P in feed more efficiently, and to reduce the amount of N and P fed.

The first step in these strategies is to set reasonable production goals. If animals are fed for higher production levels than they can reach, extra nutrients will simply be excreted. This is expensive as well as environmentally hazardous. Grouping animals according to their production levels will allow more precise matching of rations to production potential.

The next step is to know the animals and to know the feeds. Nutritionists at the university or feed dealers will be able to supply much more in-depth information about feeds and animals than this article can.

Phosphorus. Animals are able to extract only part of the P from the feeds and supplements they eat. The amount they extract is "biologically available." Of course, the amount they do not extract is "unavailable" - and will be excreted without being used.

Providing feedstuffs which are high in available P helps animals make more efficient use of P in the feeds. So, less total P can be fed than if animals are given feedstuffs low in available P.

Test feedstuffs, including forages, for their nutrient content and find out which feed sources will provide readily-available nutrients to your animals. You may be able to cut back on some supplements - which will reduce nutrient excretion and also expense.

Nitrogen. Avoid excessive protein feeding; it is expensive and causes high N excretion. Setting reasonable production goals and knowing animal protein requirements at different production levels is critical in feeding appropriate protein levels.

Know animal requirements for different amino acids. Feeding high-quality protein supplements which are well-balanced in amino acids will lower the total amount of protein required in a diet, particularly for swine. The use of poorly-balanced protein supplements can cause overfeeding of several amino acids in an attempt to meet animal requirements for one or two amino acids.

For ruminants, particularly dairy cows, consider protein "fractions" in feeds - some feeds contain protein which bacteria break down in the rumen. Cows also need protein which bacteria cannot degrade. If cows do not have sufficient non-degradable protein, they need more total protein.

To reduce total crude protein in the diet and improve milk production, supplement highly degradable protein sources with ones that are not so degradable.

Ration balancing for nutrient management requires a great deal of thought. But keeping high production and profits while maintaining a clean environment is well worth the trouble!

Cromwell, G.L. 1995. Nutrient Management from Feed to Field. Presented at the World Pork Expo, Des Moines, Iowa, June 9-10, 1995.

Grant, R.J. 1996. Feeding Dairy Cows to Reduce N, P, and K Excretion into the Environment. Presented at Area Dairy Days, Nebraska, March 4-8, 1996.

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