Even though it may be a least-cost ration, don’t go overboard on corn. Studies show that cows need a sizeable percentage of crude protein from non-corn sources for maximum milk output.
Everything seems to be made from corn, including most of our feed ingredients and byproducts. But cows will not perform as well when too much of the diet is made up of corn products.
We feed corn silage, corn grain, corn hominy, corn distillers grain, corn gluten feed, corn gluten meal, corn germ meal . . . corn, corn and more corn. But the protein in corn and corn byproducts is all basically the same. Some are more rumen degradable; some have more bypass protein, but the amino acid composition is similar.
Corn protein doesn’t supply all the essential amino acids needed for optimum milk yield and milk protein. Corn protein usually doesn’t supply adequate lysine. So, we end up feeding more crude protein than is needed to attempt to satisfy the amino acid requirements of the high producing cow. This wastes protein, limits other essential nutrients and results in excess environmental nitrogen excretion.
We have nutritional modeling programs that help us predict the amino acids provided by the rations and required by cows. A study reported in the April issue of the Journal of Dairy Science helps to quantify what most nutritionists inherently know and models predict. The researchers did a meta-analysis of milk and milk protein production on diets with varying amounts of corn protein. A meta-analysis is a statistical combination of many different studies to look at specific variables, e.g. milk vs. level of corn protein.
The study concluded that diets should contain at least 6.5% crude protein (% of dry matter) from non- corn sources (soybean meal, alfalfa hay, whole cottonseed, canola meal or others). Maximum milk production and milk protein was achieved when non-corn crude protein was 8.5% of dry matter.
So, feeding too much corn or corn byproducts reduces milk revenue even though it may be a least-cost ration. Don’t go overboard on corn. Balance corn protein with adequate protein from other sources, especially those that supply lysine.
Reference: Hollman,M., M.S. Allen, and D.K. Beede. Dietary protein quality and quantity affect lactational responses to corn distillers grain: A meta-analysis. Journal of Dairy Science. 2011; 94:2022-2030.