Wet corn gluten feed can be an excellent addition to a ration based on dry corn silage as it will bring moisture to the ration, improve intake, and can substitute for wet brewers grain or other ingredients. You could go as high as 25% of the total ration dry matter or 12 pounds of dry matter (the wet pounds would depend on the moisture content of the wet gluten) assuming the price is right. Check starch and NDF levels in the final diet to ensure that wet corn gluten feed is not included in excess. The phosphorus concentration of corn gluten feed is much higher than corn, so the total phosphorus in the ration and its impact on nutrient management must also be considered.
Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET
