This could be related to low rumen pH. Check your DHI records to see how many cows are below 2.8% milk fat. Possibilities include: • increasing the NDF (if it is below 28%), • checking total ration dry matter (is it between 35-50% moisture?), • considering adding sodium bicarb (half a pound per cow per day), • lowering starch levels using a by-product feed or more forage, and • checking the physical form of the ration. Also determine if the cows are sorting the balage out of the diet and effectively consuming a low forage diet. This assessment can be completed using the Penn State particle separator. The balage should be over 170 RFV. Also, it can be related to fat source and amount being fed, so check the amount of ruminally unprotected fat in the diet. Current research suggests polyunsaturated fats (vegetable fats) in the diet can be converted to compounds in the rumen that act on the udder to inhibit milk synthesis and reduce milk fat production. Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET Robert Van Saun, Extension Veterinarian, Penn State University

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