There are three stages to the corn harvest in Manitoba. The first starts in September when the corn crop matures and whole plant moisture dries to about 35 per cent dry matter — it’s one of the best time to take off corn silage. The second occurs weeks later when the grain corn dries to about 75 per cent dry matter; that’s when to harvest high-moisture corn. Finally, when the same corn kernels drop below 15 per cent moisture; it should be combined.
As a dairy nutritionist, it has been my experience that even modest changes to the moisture content of corn silage compared to high-moisture or dry corn has a significant impact on the amount of nutritious feed eaten by lactating dairy cows. I strongly recommend that dairy producers test corn silage moisture content after a new bag, bunk or silo is opened.
The value of knowing the new corn silage’s moisture is easily illustrated. An early-lactating dairy herd eats 90 lbs. of a dairy diet with a total moisture content of 50 per cent, which translates into a base consumption of 45 lbs. of dry matter intake (DMI). Now, let’s assume the moisture content of new bunk of corn silage making up 40 per cent of this lactation diet is really 67 per cent moisture rather than an estimated 60 per cent moisture. The actual diet is about three per cent wetter than estimated (52.8 per cent moisture). The real DMI of the herd could drop by 2.5 lbs. with a potential loss of about five lbs. of milk per cow may result (re: one lb. DMI = 2.0-2.5 lbs. milk produced, source: University of Illinois).
Good to know
This is useful information when corn silage is excessively dry, because it will significantly decrease the final moisture content of the entire dairy diet. An excessively dry TMR has a low physical density, which allows dairy cattle to separate the finer grain and protein supplement material from coarser forage fibres.
In order to achieve this goal, dairy producers can add up to seven kilograms (15 lbs.) of water per lactating head into a TMR diet to bring its moisture content into a 50 per cent optimum moisture range. For example, adding 10 lbs. of water to a TMR of 40 per cent moisture (with very dry corn silage) and fed to lactating dairy cows at 80 lbs. per head per day can increase this dairy diet’s moisture content to a more plausible 47 per cent.
Moisture testing methods
Whether dealing with ideal, wet or dry corn silage, the dairy producer should choose the best method that works for them in determining the moisture content of post-ensiled corn silage samples. While there are many ways to test moisture content in feeds, I like the two easy-to-do approaches; namely, using a Koster tester or by microwave oven (MV).
The moisture-content procedures for both methods are virtually identical:
- Weigh out a 100 to 500 grams corn silage sample representative of harvested fields on a gram-weighing scale.
- Corn silage samples can be dried by either the Koster tester or microwave oven.
- Re-weigh dried out corn silage samples and,
- Calculate moisture results; per cent moisture content = ((Initial sample wt. – Dried sample wt.)/Initial sample wt.) x 100. If a 500-gram corn silage sample is dried to 184 grams, its moisture content would be 36.8 per cent.
The electric Koster dryer is specifically designed for drying forages and wet feeds, and determining their moisture content. This apparatus has a heating element and built-in fan to blow hot air through the feed sample placed on a built-in screen. Its drying procedure takes about 20 to 25 minutes. Sample loss tends to be a small problem in using the Koster tester.
The common microwave oven provides a quick means of also drying samples. Its greatest challenge is to avoid burning samples, when they get crispy (it’s recommended to place a small amount of water in oven). MV drying time is about five to 10 minutes for most wet feeds. Regardless of the method it sometimes takes a bit of practice to refine procedures in order to achieve the most accurate moisture results.
On occasion some dairy producers might find the tested moisture of their current corn silage is higher than expected. That’s because most whole corn plants despite looking brown and wilted when chopped often contain considerable moisture, because their numerous ears contain more water than expected.
Some dairy producers were proactive and took pre-harvest corn silage samples. They did this by a sweep of a harvester or yard-cutter, which allowed them to possibly delay harvest and allowed standing corn plants to wilt further. This corrective opportunity tends to avoid excessively wet corn silage (greater than 75-80 per cent moisture) going into the bunk; which contributes to a greater loss of nutrients during the ensiling, storage and feed-out processes.
We should still moisture test more samples of corn silage when the bunk or bags are finally opened. This is the corn silage that will be fed to the lactating dairy cows and most dairy diets. The feed value of corn silage will be impacted by its moisture content (as demonstrated above). It is important to know the actual moisture content of incorporated corn silage in order to formulate a well-balanced dairy diet.
Periodically, we should test the moisture content of the final TMR diet, so we can make further adjustments, so milk production by lactating cows is optimized.