Unusual “Case Studies” from the Autumn of 2008

Brad Oldick, Ph.D., Dairy Nutritionist

I recently wrote an article for The Redline that discussed “Corn Silage Slump.” Since then, corn silage has been busily fermenting in silos across our trade area. In many instances, cows have been switched to a 2008 crop high-moisture or dry-corn grain, as well as 2008 crop corn silage. I have had a handful of experiences with this year’s switch to new crop feeds that are unusual enough to justify sharing them.

In general, chemical analysis of corn silage did not show anything particularly unusual about the new crop. It was generally a bit lower in starch and sugar and subsequently slightly higher in fiber and lower in energy than typical book values. However, this could all be dealt with during ration formulation by feeding slightly more corn and balancing for appropriate levels of NFC and starch…right? You could also consider adding sugars to the diet. In a handful of cases, over time, I found these assumptions to be very wrong. They became even more wrong when we switched to new crop corn grain.

The herds where I had the most trouble lost over 10 lb. of milk production per cow per day when switched to new crop corn silage. This is far in excess of the expected 3 to 5 lb/head/day drop. Each herd would typically milk in the mid 70’s (it is noteworthy that the highest producing herds that I work with (80 to 95 lb/head/day tank averages) had a much smoother transition onto new crop silages). I had increased the amount of corn grain in each of these herds until NFC was somewhere between 40 and 43% as a proactive measure to try to avoid the typical corn silage slump (all herds are TMR fed). Milk fat and protein did not decline and, in some instances, increased slightly. Cud chewing remained excellent with over 80% of the cows lying, chewing their cud. Milk urea nitrogen values increased in each case, some as high as 19 to 20 mg/dl on diets balanced to 17.5% crude protein and containing no NPN.

When we experienced these drastic drops in milk production, the first step we took was to add supplemental sugar from either liquid molasses or Rumin 8. This did not improve milk production or affect milk components in the herds that saw the most severe drops in production. Although I was very uncomfortable doing it, the next step taken was to increase corn grain in the diets. This seemed to be the “solution;” we gradually increased corn grain in the diets, replacing forages, until the NFC’s reached levels as high as 45% with forage NDF values at 20% of diet dry matter. This resulted in a steady increase in milk production across all cows to within 3 to 4 lb/head/day of the production before new crop feeds were introduced into the diet. Milk fat and protein were not compromised and MUN values declined to within a couple of points of pre new crop values.

Now begins the task of monitoring the situation in these herds very closely. If the starch in the corn silage and/or high moisture corn grain suddenly becomes more available, we could see a sudden drop in milk fat, intake, cud chewing, cow health, etc. We need to check these parameters daily so that we can react very quickly before we have a herd crisis.

The bottom line is that the cows told us what we needed to do (low milk with high butterfat and MUN indicates not enough available starch) when the rations on paper indicated we could not push any more corn to the cows. If you have herds that are experiencing these struggles, working outside the standard guidelines may be the solution; I would be glad to help any of you navigate these situations.