The ratio of alfalfa silage to corn silage and the amount of crude protein in diets fed to late-lactation cows influences the potential for nitrogen loss to the environment.

Researchers at the University of Wisconsin fed 24 late-lactation cows one of six diets consisting of either an alfalfa-to-corn-silage ratio of 70:30 or 30:70, plus one of three levels of crude protein — 15 percent, 16.5 percent or 18 percent.

Cows fed a diet containing the 30:70 alfalfa-to-corn-silage ratio, plus 18 percent crude protein, excreted 76 grams more nitrogen in their urine than cows fed a diet consisting of the same forage ratio, but only 15 percent crude protein. The table below summarizes nitrogen levels in the cows’ manure and urine for each of the six diets.

The results suggest the ratio of alfalfa silage to corn silage and the crude protein percent of late-lactation diets strongly influences the potential for nitrogen loss to the environment.