Editor's note: The following Practice Builder is excerpted from a presentation at the Western Canadian Dairy Seminar in March by Normand St. Pierre and Bill Weiss, dairy scientists at The Ohio State University.

The composition of all feeds varies. However, the probability that all feeds in a diet will have a lower- than-expected concentration of a given nutrient on a given day is low. Some feeds will have higher-than-expected concentrations; others will have lower-than-expected concentrations. Therefore, the variation in nutrient composition of feedstuffs is usually greater than variation in nutrient composition of the TMR (assuming good, standard feeding practices are in place). The impact of variation in the composition of feedstuffs is reduced as more feeds are included in the diets. Relying on a particular feedstuff that is highly variable in crude protein concentration to provide a large proportion of dietary crude protein increases the risk of being wrong. (In example shown in the proceedings of the Western Canadian Dairy Seminar), the concentration of crude protein in 10 different loads of corn gluten feed varies from 19.4 percent to 33.4 percent, with a mean of 22.9 percent. The load-to-load variation appears quite high. However, if the TMR was balanced for 17 percent crude protein, using the mean value for corn gluten feed, and the diet contained 10 percent corn gluten (DM basis), the variation in the concentration of crude protein in the TMR is much smaller and ranged from 16.6 percent to 18 percent. Using a wide variety of ingredients in a TMR and not relying too heavily on a single ingredient is probably the best way to reduce the visible and hidden costs associated with variation.