By Rick Lundquist, Ph.D.
A small group of dairy nutritionists recently shut ourselves in a room for a day-long discussion about corn. This may sound like a pretty “dry” day (my kids think I’m geeky), but it was really a very stimulating discussion.
The discussion was led by Pat Hoffman of the University of Wisconsin. Pat is kind of the “Indiana Jones” of corn in dairy nutrition. I say this because he uncovered the “holy grail” of all that is known about corn by revealing a wealth of corn knowledge which has heretofore been kept secret from dairy scientists, buried within the Cereal Chemistry Journals (or “scrolls”, if we’re going with this analogy).
Corn is a seed, and if we understand how it functions as a seed, we can more fully understand how it functions as a feed. A corn seed is made up of the pericarp, germ and endosperm. The endosperm contains mainly starch and protein. About 60% to 70% of the protein in corn is in the endosperm. This is where distillers grains comes from (after the starch is fermented for ethanol).
Prolamins are proteins in the endosperm that encapsulate the starch granules, which is the energy source for the seed until it sprouts leaves for photosysnthesis. Prolamin protein in corn is called zein. Prolamin is like the lignin of corn grain. The higher the prolamin content, the lower the starch degradability in the rumen, because the starch granule has greater protection against bacterial attack. Fine grinding of corn disrupts the prolamin matrix and increases bacterial attachment sites, which increases starch digestibility.
Prolamin content of various cereal grains is as follows: wheat<barley<rye<oats<corn<sorghum. This is also the relative order of germination temperatures of these grains.
All corn is not 9% crude protein. Higher protein corn has lower starch degradability because it contains more prolamin; lower protein corn has greater starch degradability. If your corn grain tests 6% protein or 11% protein, don’t assume the lab is wrong. Acid detergent fiber (ADF) and neutral detergent fiber (NDF) are not related to starch digestibility in corn grain. These tests were designed for forage fiber.
Proteolysis during fermentation degrades prolamin in high moisture corn (HMC), which is why HMC starch degradability increases during fermentation. This is also why HMC feeds like corn in the fall and rocket fuel in the spring. As proteolysis proceeds during fermentation, prolamin and other proteins are converted to ammonia. The ammonia levels in HMC, along with other fermentation indicators can help us predict the functional starch-protein matrix in HMC and the relative degradability of the starch.
If this brief discussion piques the interest of any other potential "corn geeks," you can read much more about the science of corn grain on the University of Wisconsin Dairy Science Web site at www.dysci.wisc.edu. Click on “extension” and “dairy cattle nutrition.”
Hoffman and others have incorporated the cereal science knowledge into practical equations to evaluate feed grains fed to dairy cattle.
Rick Lundquist is an independent nutrition and management consultant based in Duluth, Minn. Contact him at firstname.lastname@example.org.