It’s that time of year when harvested forages are tested for their nutrient content and an emailed back analysis sheet can list up to 80 laboratory results for each forage sample submitted.
Much of this data can be inputted into dairy ration balancing software to develop on-the-farm TMRs that supply essential nutrients in the right amounts required by high-milk performing dairy cows. However, much of these analytical results are secondary without a respective and simple moisture analysis taken on each collected forage samples in the first place.
The moisture content of forages and other feedstuffs has the greatest impact upon feed consumption and thus nutrient intake by dairy cows. Rations containing more than 50 per cent moisture are often associated with reduced dry matter intakes by dairy cattle. As their diet becomes increasingly wet, the essential nutrients locked in the “dry” feed become less concentrated. The animal must eat more total ration in order to consume the same amount of nutrients or dry matter feed as before. Given that moisture also adds bulk to the ration, there is a point where a dairy cow can consume only so much “as fed” ration (dry matter feed + moisture) because of gut fill.
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It is estimated most mature dairy cows can consume up to 45 kg (100 lbs.) of “as fed” feed while first-calf heifers consume between five to 20 per cent less feed. With these feeding boundaries in mind, we should target 45 to 55 per cent moisture in the overall dairy diet to accommodate sufficient dry matter intakes of between 22 and 25 kg of dry feed, particularly in early lactation cows that parallels another rule of thumb: one kg of dry matter intake yields two kg of milk production.
Modest changes matter
Since forages make up the majority of most dairy TMRs, we should also be aware that even modest changes to the moisture content of the “wet forages” such as corn/barley silages and alfalfa/grass haylages can significantly increase or reduce the amount of nutritious feed eaten by the cows, and be turned into milk. Other “wet” feeds such as brewer’s mash (20 per cent DM), liquid whey (10 to 15 per cent DM) and molasses (75 per cent DM) also have secondary moisture content effects upon the final dairy diet. Last, moisture content of well-cured hay is less variable and tends to have smaller influences, respectively.
For example let’s examine the impact of a five per cent moisture content increase of forages formulated in a dairy diet designed for early lactation dairy cows.
Whether we fail to analyze moisture content of our forages, or there is an actual absolute five per cent increase in moisture content of our dietary forages, the following impact upon our virtual dairy feeding program results.
“As-fed” intake does not change at 41.5 kg per lactating dairy cow.
Total dry matter intake drops from 23.6 kg to 22.0 kg per head or a seven per cent decrease.
DMI per cow of corn silage and alfalfa hay drops by 1.2 kg and 0.4 kg, respectively.
Overall dietary moisture content increases by only 3.7 per cent.
Forage: Concentrate ratio (dm, basis) falls slightly from 62.7 per cent to 60 per cent.
From above points, the most significant moisture content impact — is a “total dry matter intake of drops by seven per cent,” which leads to a probable decrease in milk production of 3.2 kg per early lactation cow (re: 1.6 kg x 2). Therefore, it is a strong recommendation that dairy producers test forages for moisture content before feeding them in a TMR to their dairy herd.
How to test
Given such a major impact upon feed and management in the dairy barn, producers should choose an actual method that works best for them in determining the moisture content of dairy forages, particularly their wet forages. While there are many ways to test moisture content in feeds, there are presently two popular “old school” approaches; namely, using a Koster tester or by Micro-wave oven (MV).
The moisture content procedures for both methods are virtually identical: (1) Weigh out a 100 – 500 gram silage/haylage sample that is representative of harvested fields on a gram-weighing scale. (2) Samples can be dried down by either the Koster tester or Micro-wave oven. (3) Re-weigh dried out silage/haylage samples and (4) Calculate moisture results; per cent moisture content = (initial sample wt. – dried sample wt.)/initial sample wt.) x 100. Therefore if a 500-gram corn silage is dried down to 184 grams, its per cent moisture content would be 36.8 per cent.
Interestingly, the Koster tester is an electrical dryer that is specifically designed for drying forages and wet feeds, and determining their moisture content. This apparatus has a heating element and fan built in its base by which hot air is blown through the feed sample placed on a built-in screen for moisture determination. Its drying procedure takes about 20 to 25 minutes.
Sample loss tends to be a small problem in using the Koster tester. Likewise, the common micro-wave oven provides a quick means of also drying samples. Its greatest challenge is to avoid burning samples, when they get crispy (re: 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 which methods is preferred in determining the moisture content of one’s silage, haylage and other forage, it sometimes takes a bit of practice to refine their similar procedures to achieve the most accurate moisture results.
Accurate moisture results of the forages are primary to targeting dry matter feed consumption of a well-balanced dairy diet and subsequent milk production in the lactating dairy herd. Producers should routinely test and take the necessary corrective action to maintain the optimum level in their dairy diets for primary milk performance and revenue.