Watch Corn Silage Moisture, Not Just Milkline

Nutrition Update
Volume 8 No.2, August 1997

Recent research and on-farm experiences suggest that we haven't been getting as much "milk" out of corn silage as we might. The problem is that we have been determining when to chop corn based on milkline rather than moisture content.

Moisture levels at one-half to two-thirds milkline, the standard recommendation, can vary significantly. With the variation in moisture at similar milklines comes significant differences in milk production (Table 1). As the plant matures ie. dries down, the digestibility of both the starch and fiber components decreases. Moisture content is a much better gauge of how digestible corn silage will be than milkline.

Randy Shaver, extension dairy specialist at the University of Wisconsin, recommends that corn silage be chopped at about 70% moisture for the highest possible milk production. In essence, this means most people using bunker silos or bags will want to start chopping at 70% and hope they can finish before the corn gets below 65% moisture. Shaver recommends that people wait until their silage corn appears to be at one-fourth milkline and then start checking moisture and chop accordingly.

Shaver suggests an average moisture of 62 to 65 % for top-unloading silos and not less than 60% moisture for corn going into sealed uprights. Any time corn silage is drier than 60% moisture, regardless of how it's stored, we should question how good a source of nutrients it's going to be for high-producing cows. Perhaps we should keep dry corn silage separate, if at all possible, to feed to heifers and dry cows.

Table 1. Effect of corn silage moisture on how cows milk