Dairy operations can feed cows economically with high-forage diets using corn silage as the sole source of forage. Whether you are feeding a high-corn silage ration today or are considering it in the future, producers should consider several management factors when feeding high rates of corn silage.
1. Evaluate silage kernel processing
The starch in corn silage is a valuable commodity today, but the kernels have to be damaged sufficiently to allow complete starch digestion. Sending off a sample for kernel processing analysis can help a nutritionist better estimate how well starch will be digested in the rumen and small intestines. Analyzing fecal starch levels can show if poor processing is allowing starch to escape into the manure. Fecal starch levels exceeding 5 percent likely need ration evaluation and adjustment.
2. Watch the starch
High levels of starch in corn silage have often been blamed for low butterfat tests, underperformance or inconsistency in manure scores.
However, this has become a very manageable nutrient with improved lab testing. Laboratory starch analyses are helping nutritionists factor in the effect that time in fermented storage has on increasing ruminal starch availability. Nutritionists now know to reduce the amount of supplemental grain being fed in a high-corn silage diet to complement the high starch levels being delivered by today’s elite corn genetics.
From the point of ensiling until six months later, the starch digestibility in corn silage can increase by as much as 20 percent. This means that diets formulated with 26 to 28 percent starch last fall may have to be lowered to starch levels closer to 23 to 25 percent to account for increased starch availability.
Watch the use of high-moisture corn or snaplage in the diet, as they will also have elevated ruminal digestion rates this late into the storage season. Dry corn may be a better grain source in very high-level corn silage diets.
Approximately 65 percent of the energy in corn silage comes from starch, so having a high starch level is certainly beneficial to overall ration costs.
3. Watch effective fiber
If the chop length of the corn silage is short, it may be necessary to find an effective fiber source such as poor quality hay or straw to create a rumen mat matrix to help stimulate cud chewing and the production of saliva to buffer rumen acid production. Evaluating the freshly delivered TMR and the refusals after three to four hours in the feedbunk with a Penn State Particle Separator can determine if adequate effective fiber (top screen) is present and if any sorting has occurred (more than a 10 percent variance in amounts of the different screens from freshly delivered to sorted refusals).
4. Keep supplemental fat within reason
A review of tallow supplementation (2 percent of the ration) in high-corn silage rations showed some tendency to reduce intake and lower fat test, although cause and effect are not fully understood. Fat test problems can be avoided with our understanding of the trans-fatty acid theory of butterfat depression along with the ability of newer ration software to track estimates of unsaturated (especially linoleic acid) intakes.
5. Consider protein
To have success with a high-corn silage ration, both protein quantity and quality need to be taken into consideration. It is important to have ample crude protein (CP) and rumen-degradable protein (RDP) in order to stimulate microbial protein synthesis.
High-energy corn silage will grow lots of rumen bacteria, which the cow will digest as a high-quality protein source. Field success has been achieved in rations containing upwards of 25 pounds of dry matter (DM) from high-starch corn silage by targeting 16 to 17.5 percent CP levels with conservative levels (8 to 8.5 percent DM) of ruminally degraded protein to fuel bacterial needs and attend dietary lysine and methionine levels.
6. Avoid feeding high-corn silage rations to dry cows and heifers
Exclusive corn silage rations are not suitable for feeding to dry cows and heifers. These energy-rich diets often result in fat heifers and problems for dry cows. 
Dann Bolinger is a dairy specialist with DuPont Pioneer based near Lansing, Michigan.
PHOTO: Cows at South Ridge Dairy in southern Idaho are fed rations that include corn silage, hay, beet pulp and potato waste. Photo by Lynn Jaynes.
