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Moisture is a worthless, confusing component of all feed ingredients. Because it is has no value, moisture has a big (but often hidden) impact on the accuracy and economics of feeding cattle. Most feedlot diets contain high moisture ingredients such as silage, therefore moisture levels need to be considered when formulating diets and making bunk calls. We are so used to working with the moisture in feeds, we often don't appreciate how it inflates value and complexity. Most feedlot nutritionists balance nutrients and ingredients with moisture removed (dry matter basis). Most additives are cleared to be fed at a specified concentration of the dry matter. Intakes of cattle are limited primarily by dry matter content of the diet.
Working with dry matter is unfamiliar to most feedlot managers. However, once accustomed, working with dry matter is actually simpler, especially since calculations are automatically done by Fusion. In the following discussion, AF = "As Fed" (what is actually fed). DM = dry matter (all moisture removed).
If we have a diet that is 50% barley (88% DM) and 50% silage (35% DM), 100 pounds of this mix contains (50*.88=) 44 pounds of barley DM and (50*.35=) 17.5 pounds of silage DM. So in 100 pounds (AF), this mix contains 44 + 17.5 = 61.5 lbs total DM (61.5% DM). The dry matter formula contains 44/61.5 = 71.5% barley and 17.5/61.5 = 28.5% silage. When the water is removed we see this ration contains a lot more grain than is evident in the as fed formula.
Most additives are to be fed as a concentration of the dry matter. For example, if a feedlot is providing monensin through a supplement and targeting 33 mg/kg of diet DM, the supplement must be included at a constant percent of the diet dry matter. Maintaining a consistent concentration of the dry matter is simple when formulas are entered on a DM basis; Fusion automatically does the math, the feed crew won’t even notice. For perfect accuracy, ration AF formulas (but not DM formulas) should change with changes in ingredient DM. Fusion automatically makes these adjustments when rations are entered on a DM basis (but not when entered on AF basis). When formulas are entered on an AF basis, feedlots typically rely on a nutritionist to do these calculations. As a result, ingredient dry matters aren’t adjusted very frequently, reducing accuracy of dry matter intakes, feed conversions, and costs of gain.
At a typical feedlot that makes bunk calls as total pounds AF, bunk calls can vary by over 2-3 fold across pens. This variance is due primarily to differences in head count and ration moisture. Obviously, if a pen has twice as many cattle in it, it will require about twice as much feed. Similarly, rations with vastly different moisture content will have large differences in pounds AF required. For example, if potatoes were introduced in a finishing diet, AF (but not DM) intake would suddenly increase due to the high moisture content of potatoes. As well, as cattle are stepped-up on feed with reducing levels of silage, AF intakes may decline. Although other variables such as animal size and energy content/digestibility influence intakes of a pen, the primary factors are animal numbers and moisture content. Making bunk calls as pounds of dry matter per animal removes these variables so bunk calls are more meaningful and consistent across pens. The value of working with dry matter is amplified when feeding high moisture products like silage and potatoes.
Again, adoption of this new way of making bunk calls will be simplified if you abandon old thinking rather than always trying to convert back to it. The following thumb rules may help adopt this new logic:
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