Fecal Starch Analysis: Finding the Hidden Profit Leaks in Your Manure

Starch is one of the most powerful and expensive energy sources in dairy and beef cattle diets. Whether you are feeding steam-flaked corn, high-moisture corn, or corn silage, your goal is simple: maximize the amount of starch the animal actually digests to fuel milk production or weight gain.

But how do you know if your cattle are actually absorbing that energy or passing it straight into the manure pit?

Enter Fecal Starch Analysis. This simple laboratory test acts as an evaluation report for your grain processing and feeding management, revealing exactly how much dietary energy is being wasted.

What is Fecal Starch Analysis?

Fecal starch analysis measures the concentration of residual starch remaining in cattle manure (expressed as a percentage of fecal dry matter).

Because starch intake and total tract starch digestibility (TTSD) are tightly linked, researchers have established a direct mathematical relationship: every 1% increase in fecal starch represents a 1.25% drop in total tract starch digestibility.

If your cows are passing too much starch, they aren't getting the net energy they need. In fact, for every 1% increase in fecal starch above the ideal threshold, dairy cows can drop roughly 0.7 pounds of milk per day. On a feedlot, higher fecal starch means you must buy significantly more grain to achieve the same growth performance.

How to Interpret Your Fecal Starch Results

Once you send your manure samples to a wet-chemistry lab, your results generally fall into two categories:

1. Optimal: Less than 3% Fecal Starch

• What it means: Your cattle have a total tract starch digestibility greater than 96%.

• Action item: Your current grain processing, moisture levels, and ration fermentations are hitting the sweet spot. Maintain your current nutritional management baseline.

2. Suboptimal: Greater than 3% to 5% Fecal Starch

• What it means: There is a clear opportunity to capture lost energy and improve feed efficiency.

• Action item: You need to investigate why the starch isn't breaking down.

Common Causes of High Fecal Starch

If your test scores come back high, it is rarely a problem with the cow's biology—it is almost always an issue with feed engineering or storage. Look closely at these four areas:

• Poor Grain Processing: If the particle size of dry or high-moisture corn is too coarse, digestive enzymes cannot penetrate the kernel effectively. For dairy cows, a grind size of 500 microns for dry grain is highly recommended.

• Inadequate Kernel Processing in Silage: If the kernel processor on the forage harvester is improperly set, whole or half kernels will pass straight through the digestive tract entirely untouched.

• Dry Ensiled Feeds: Forages and grains with low moisture levels (<35% moisture for corn silage) naturally exhibit lower starch digestibility compared to wetter feeds.

• Short Fermentation Times: Starch digestibility naturally improves the longer a feed sits in fermented storage. Transitioning to "new crop" silage that has only fermented for a short time frequently triggers a spike in fecal starch. Aim to let ensiled starch sources ferment for at least 4 to 6 months before feeding.

Best Practices for Taking a Fecal Sample

Getting accurate lab data depends heavily on your sampling protocol. Because individual cows digest feed differently, a single grab sample won't cut it.

1. Collect Pen-Based Samples: Gather fresh, undisturbed fecal piles from at least 8 to 10 different animals within the same management pen.

2. Homogenize: Combine all the samples into a clean bucket and mix them thoroughly into a single, uniform blend.

3. Package Wisely: Scoop roughly 2 cups of the mixed manure into a plastic shipment container. Do not fill the container more than 2/3 full. Fermentation generates gas, and leaving headspace prevents the container from bursting in transit.

4. Chill and Ship Fast: Cool or freeze the sample immediately to halt ongoing bacterial fermentation, which can degrade and artificially alter starch levels before the lab can analyze it.

If you adjust your ration or grain processing based on your results, wait 2 to 3 weeks for the cattle's digestive tracts to fully adapt before pulling a new sample to re-evaluate.