Animal nutrition will have a strategic responsibility in the forthcoming regulatory process related to environmental stewardship. At the farm level, the two areas to work with dairy cow nutrition will be:

•feeding management to minimize nutrient excretion while maintaining economical efficiency
•estimation of nutrient excretion and manure chemical composition

A recently published paper in the Journal of Dairy Science discussed the advances in animal nutrition and sustainability. The authors point out that over the past 100 years, numerous studies have demonstrated a dairy cow’s nutrition has a major impact on productivity. Unfortunately, the dietary intake or density of a nutrient at which efficiency is maximized is different than that which maximizes profits.

For example, one of the researchers extensively studied the efficiency of dietary protein content for milk yield. One of the main conclusions was that for a herd with an average potential of 35 kilograms (77.2 pounds) of milk per day, the maximum physical efficiency of a diet is achieved at a crude protein content of 14.9 percent, whereas maximum economical efficiency is achieved at a crude protein of 18 percent. More protein in the diet generates more net income, but it also leads to more nitrogen being excreted.

According to the authors, one possible solution is to assign an economic cost to nitrogen excretion, and the maximum economic efficiency likely will occur closer to the point of maximum physical efficiency. For the previous example, the U.S. official system predicts a requirement of 15.2 percent of crude protein content in the diet, which is the result of rumen (9.7 percent) and intestine (5.5 percent) requirements. But these two are equivalent to the U.S. crude protein requirement only if the rumen and the intestine requirements are perfectly balanced, which is difficult managing different feedstuffs, byproducts, prices and crude protein contents in feeds.

Other researchers working under controlled conditions suggest no increase of milk yield or milk protein can be expected for dairy cows with more than 16.5 percent crude protein in the diet. The complexities of protein nutrition and limitations in measuring nitrogen fractions in feed make accurate specifications for feed protein fractions difficult.

For commercial dairy farms trying to maintain a positive cost/benefit relationship, a safety margin of crude protein content in the diet should be considered. In terms of animal performance, VanderHaar and St-Pierre indicate the economic risk of underfeeding protein in dairy cows is greater than the risk of overfeeding protein, so protein efficiency has not been maximized in the past, nor is it likely to be maximized in the near future.

In respect to the second point (manure composition), important data was recently published by the American Society of Agricultural Engineers. Nevertheless, more information is needed.

The question is, “Is animal nutrition a very important tool to estimate manure nutrient composition?” Some of the answers may be:

1. It is difficult to control all the input in a typical (California) dairy farm; they are highly intensive to manage and interact with other systems.

2. Because more than 80 percent of the total inputs in a typical dairy farm are feeds, and because fertilizers (5 to 15 percent of the inputs) can be reduced with good manure management, it should be possible to estimate a feed’s inputs through nutrient intake, as well as manure production and composition, with the software used to balance diets.  PD

References omitted due to space but are available upon request.

—From University of California Dairy Notes, April 2006

Alejandro R. Castillo, Extension Dairy Farm Adviser, University of California