There has been a lot written and discussed about increasing the digestibility of starch in dairy diets, and for good reason. Starch comprises, on the average 25% of most dairy rations. Increasing the amount of starch digested in the rumen and available to produce microbial protein can bring big dividends to the bottom line.
Because of corn being grown for livestock feed is such a small percentage of the total crop, and corn grown for ethanol production has increased dramatically, the genetics of the plant have changed. This change to enhance ethanol production has resulted in corn grain that is lower is digestibility. Therefore everything we can do to enhance digestibility has that much of a greater impact.
When I speak about increasing digestibility, I am referring to digestibility in the rumen. Even our less digestible corn is digested over 95% by the time it passes through the digestive tract. Cows can still get energy from corn in the intestine, but our goal is to produce as much microbial protein in the rumen and for this we need digestible starch. Too much starch digesting or fermenting in the intestine can cause health problems.
There are three main ways to ensure we increase starch digestion in the rumen. We must pick the right genetics. Make sure the corn in both grain and silage is processed correctly. We also must add additives that help with starch digestion, such as enzymes.
As mentioned before, genetics can play a big role in starch digestion. Unfortunately, especially for corn grain, most dairies don’t have an option as to the varieties grown. For those that do there are still companies producing some older genetics that would be worth checking into. Silage is a different matter. Searching for varieties with starch digestibility numbers is a very worthwhile project. All feed labs now have the ability to test for digestible starch. Using these numbers to rank your current varieties and pick the best ones for next year can help.
The area where we can have the most immediate impact is the processing side of the equation. I think most dairies realize the importance of kernel processing in silage. But I find far less that scrutinize their corn grain as much. Currently most dairies use either steam flaked or ground corn. Let’s start with flaked corn; the digestibility of the flake is directly correlated to the flake weight. The lighter the weight the more digestible the flake. Unfortunately, a lot of mills don’t make the kind of flakes we need because of time constraints. In order to increase throughput, the flakes don’t stay in the steam cabinet long enough and therefore can’t be flattened enough to make high quality flakes. It is very easy to test flake weight on the farm. Using a very inexpensive bushel weight tester (Nasco carries them), you can determine flake weights in about a minute. Anything at or under 28 lbs. per bushel is a good flake. Above that and they become steam rolled, not flaked. The higher the number, the lower the digestibility.
Ground corn digestibility is determined by particle, or micron size. The smaller the particle the more surface area there is for the rumen bacteria to attack and digest. Going from 600 microns to 400 microns will yield about 2 lbs. of milk. The lower the micron size the longer it takes to process, so mills again are constrained by time. But we have had good luck either working with the mills to lower particle size or finding a new mill to work with.
Enzymes have a bright future in dairy feeds to increase both starch and fiber digestion. Unfortunately right now it has been hit and miss as to which enzymes work and when. There is a lot of work being done by a few companies to try to identify which enzymes work best in each situation. Shotgun feeding of enzyme cocktails is a very hit and miss proposition. But enzymes show extreme promise for taking dairy nutrition to the next level.
Bottom line is starch digestibility has a huge impact on cow performance and efficiency, and therefore profitability. There are steps that can be taken to maximize starch digestibility in your herd.