Dairy producers faced with dwindling supplies of forage and delayed planting and harvest situations may decide to increase the level of corn silage forage fed to lactating dairy cows.

Dairy Specialist / DuPont Pioneer Quebec

Feeding high-forage diets is an economical way to feed dairy cows and can be accomplished using corn silage exclusively as the forage source. There are several management concerns dairy producers should be aware of when feeding high corn silage inclusion rates in the ration.

Tips for high corn silage rations

1. Evaluate silage kernel processing. The starch in corn silage is a valuable commodity, 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. Don’t overdo the starch. Starch in corn silage is often considered the “villain” when cows fed high levels of silage do not respond as expected, experience low butterfat tests or display inconsistency in manure scores.


However, the villain image has lessened as laboratory starch analyses are helping nutritionists factor in the effect time in fermented storage has on increasing ruminal starch availability. From the point of ensiling until six months later, starch digestibility in corn silage can increase by as much as 20 percent.

This means 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 late into the storage season. Dry corn may be a better grain source in very high-level corn silage diets.

3. Watch effective fibre. If the chop length of the corn silage is short, it may be necessary to find an effective fibre 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 fibre (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 rations high in corn silage 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. Rumen bacteria will provide a lot of protein. 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 upward of 25 pounds of dry matter from high-starch corn silage by targeting 16 to 17.5 percent crude protein levels with conservative levels (8 to 8.5 percent dry matter) of ruminally degraded protein to fuel bacterial needs and attention dietary lysine and methionine levels.

6. Avoid feeding rations high in corn silage 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.