Should Major Diet Adjustments be Made Because of High Corn Prices?

Dr. Bill Weiss, Extension Dairy Specialist, Department of Animal Sciences, The Ohio State University

With the end of the cheap corn era (probably forever), diet formulation strategies are being re-evaluated.  When dry corn was $120/ton ($3.35/bu), diets that contained more than 30% starch (dry basis) were not uncommon.  The price of dry corn is currently in the $250/ton range, and dietary starch concentrations are now typically 24 to 27% of dry matter (DM).

The case for maintaining the status quo (i.e., rely heavily on corn grain to obtain diets with about 25% starch)

1. Corn grain (approximately 70% starch) is a relatively inexpensive source of net energy.  Corn may be expensive, but compared with the alternatives, it often is a bargain. Because starch is the predominant source of net energy in corn, lower starch diets can be more expensive than diets with 25% starch.

2.  Compared with other energy sources, starch often results in the greatest amount of rumen microbial protein synthesis.  Adequate dietary starch concentrations could reduce the need for expensive rumen undegradable protein.

3. On average, starch is about twice as digestible as NDF; therefore, increasing dietary starch concentrations (within limits) reduce manure output and increases feed efficiency (fat-corrected milk/DM intake).

In many situations, not changing the inclusion rate for corn grain or dietary starch concentrations is the correct decision; however, the high price of corn increases the importance of starch digestibility.  When corn was inexpensive, it was often more cost-effective to simply feed more starch than to increase the digestibility of the starch (e.g., by fine grinding or steam-flaking).  Based on a large number of experiments conducted at OARDC in which corn (grain and silage) was the predominant starch source, digestibility of starch by dairy cows fed typical diets ranges from about 88 to 96%. Increasing starch digestibility from 88 to 96% is equivalent to reducing the dietary starch concentration by 2 percentage units.   That is, a diet with 24% starch that is 96% digestible provides the same concentration of digestible starch as a diet with 26% starch that is 88% digestible.  Fine-grinding (mean particle size less than about 750 microns), steam-flaking, or replacing dry corn with high moisture corn usually increases starch digestibility.  Starch from corn hybrids with less vitreous kernels (softer or more floury) is more digestible than starch from flinty or very hard hybrids.  If you are purchasing corn grain, you will probably not know the hybrid, so this is not an option, but if you grow your corn grain, this should be one factor to consider (the effect of vitreousness is generally less for high moisture corn compared with dry ground corn).

Option 1.  Feed diets with about 25% starch but reduce the corn grain

Historically corn grain has been the cheapest source of starch in the Midwest; however, in the era of high corn prices, other starch sources should be evaluated.  Wheat and barley contain 65 to 75% starch, and their starch is usually more digestible than starch from corn grain.  Usually, but not always, they are more expensive sources of starch and energy than corn.  Because starch from wheat and barley is more digestible than corn starch, wheat and barley-based diets should be lower in starch than corn grain-based diets, which could also result in some feed costs savings.  Hominy contains about 50 to 55% starch and can be a major starch source if the price is competitive.  Hominy is higher in fat than corn grain which should limit its inclusion rate to a maximum of about 20% of dietary DM (this would provide 12 percentage units of starch).  Corn silage, depending on hybrid and maturity, contains 20 to 40% starch.  To obtain a diet with 25% starch and using average corn silage, an average Holstein cow would need to be fed about 5 lb more corn per day when fed a diet with 55% forage comprised of 70:30 alfalfa:corn silage than if she was fed a diet with 30:70 alfalfa:corn silage. 

Option 2. Feed diets with less starch (and less corn grain)

Diets with about 20% starch can support high milk yields when starch (i.e., corn grain) is replaced with non-forage NDF (e.g., soyhulls, corn gluten feed, beet pulp, etc.). A recent study from the Miner Institute (NY) found that cows fed diets with 21% starch during the first 13 weeks of lactation had similar milk yields (average 101 lb/day) and milk composition as cows fed a diet with 25.5% starch (soyhulls and wheat midds replaced corn grain).  Cows on the lower starch diet consumed more feed, resulting in lower feed efficiency.  On average, if diets are formulated correctly, cows fed lower starch diets (~20%) vs. normal starch diets (~25%) have similar milk yields and milk composition but because NDF is less digestible than starch, feed intake usually is higher, resulting in lower feed efficiency.  An increase DM intake of 3 to 4 lb/day can be expected with lower starch diets. When evaluating the use of lower starch diets, the cost of increased feed intake (without increased milk yields) must be considered in addition to changes in cost per pound of diet.