The following answer is provided by Mike Hutjens, extension dairy specialist at the University of Illinois.

Q: As corn prices have increased, the need to optimize the starch digestibility in the dairy cow continues to be important. Is fecal starch a tool to evaluate starch utilization in dairy cows?

A: University of Pennsylvania veterinarians published a formula to predict total tract starch digestibility using fecal starch and fecal lignin along with ration starch and lignin. Lignin was used as a marker to estimate starch utilization. This approach could be useful to evaluate starch utilization on farms.

With a baseline in hand, a nutritionist can tell if the farm is making improvements in processing grain and corn silage.

With well-processed grain and corn silage, fecal starch should be less than 5 percent. Yet, actual lab results presented below show that the averages are often more than that.

For each percentage point increase in fecal starch, the potential loss in milk yield is 0.7 pound per day because cows aren’t utilizing the nutrients as efficiently as they should.

The cost of a fecal starch analysis varies from $15 to $20 per sample. The recommendation is to pool fecal samples from 10 to 15 cows and submit a mixed sample requesting fecal starch.


Variation in fecal starch values reported in the field (June 2010)

No. of samples
-- Fecal starch (% DM) --
    Average Range
Dairyland Lab 379 4.7 0.2 to 40.2
Rock River Lab 52 7.9 not available
Cumberland Valley 1420 7.3 0.2 to 38.9
Pa. Vet College 515 4.6 1.0 to 11.6
University of Illinois 19 6.0 3.9 to 9.9