The dollars and sense of pretty manure

Fecal starch is a major quantifier of a TMR’s starch digestibility, which can make or break a dairy’s feeding program.  The key to determining the cause of a suboptimal fecal starch percentage is to examine the individual starch sources in the diet.

Fecal starch should be evaluated at least once per year and at least three months after putting fermented starch feeds – including corn silage, high moisture corn and snaplage – into storage. Significant changes in corn grain particle size, feed moisture and feed maturity also warrant fecal starch analysis.

Fecal starch samples should be taken from healthy high-producing or early-lactation cows. Take 10 to 12 samples from fresh, undisturbed manure piles. Samples are best collected in a jar supplied by your laboratory, with room for air between the jar and the cover.

We target fecal starch values less than 3% and total tract starch digestibility greater than 96%.  If fecal starch is greater than 3%, check the kernel processing score (KPS) of your corn silage.  If KPS is not ideal, discuss it with your team in a pre-corn silage harvest meeting, adjust rolls, and frequently monitor processing during the upcoming harvest.

Fecal starch can also be elevated in part because of coarse particles in dry corn or high moisture corn.  In this case, farms can regrind and process more aggressively, depending on the storage structure currently in use.

The economics

Research has shown milk yield is reduced by 0.7 pounds per cow with every percentage point increase above 3% (Ferguson, 2003).  Luiz Ferraretto, Ph.D., and his team at the University of Wisconsin-Madison calculated the value of lost starch in manure based on an equivalent amount of digestible starch in ground dry corn. This calculator accounts for fecal starch content, dollars per bushel of corn grain, dry matter intake (DMI), dietary starch concentration (on a dry matter percentage basis), corn grain starch concentration (dry matter percentage basis), and in vitro or in situ ruminal starch digestibility of grain corn (as a percentage of starch).

For example, consider a herd with an average DMI of 56 pounds consuming a ration that is 26% starch on a dry matter basis.  The farm’s high moisture corn is 72% starch with 78% starch digestibility.  Dry corn is valued at $4.45 per bushel.  The equivalent loss of corn grain is 1.07 pounds per cow and the cost is $0.08 per cow per day.

Reality check
From January 2023 through April 2024, we conducted a fecal starch survey on 35 herds. The data revealed room for improvement.  The fecal starch average across the herds was 3.78%. Total tract starch digestibility averaged 95.28%. The lower the number the more efficient starch can work for the cow.

Four of the farms had less than 1% fecal starch and 13 farms achieved less than 2% fecal starch.  The average corn silage kernel processing score was 72.93, the average dry corn micron size was 372, and the average high moisture corn micron size was 841.

Much variation in fecal starch exists across herds due to differences in grain and corn silage management. One of the herds surveyed is a great example. The herd started with 12.68% fecal starch. The high moisture corn was harvested at 75.41% DM and stored in a bottom-unloading upright silo. This corn was processed at feedout with an older roller mill that produced a 1,310 micron size. The herd’s average daily milk production was 90 pounds per cow, but some cows experienced digestive upsets from hindgut fermentation challenges as a significant amount of starch was passing through the rumen to the hindgut.

This farm went on to purchase a newer hammermill and processed the corn to 322 microns. Fecal starch retested at 0.31%, average milk production improved by 5 pounds per cow per day, and digestive upsets were significantly reduced.

Manure may not be a pretty thing to look at or speak about, but its significance in determining how well dietary starch is utilized by the cows is priceless. Regular starch digestibility analysis can help you identify opportunities to improve and bolster the bottom line in a marketplace where efficiencies are not a want, they are a need.