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Role of dry matter determination in management of TMRs

Steven Stewart Published on 06 February 2014

The modern dairy cow has an unparalleled ability to consume materials of little to no value for human consumption and transform those materials to food of the highest nutritional value and flavor for humans.

This ability must be supported by supplying the cow not only sufficient water but also a wide range of non-water nutrients, including protein, fiber, non-fibrous carbohydrates, fats, minerals and vitamins.

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Proper diet formulation involves providing the proper level and balance of these non-water nutrients in the “dry matter” portion of the diet. Proper feeding management involves accounting for the water present in the ingredients so that the actual (“as-fed”) amounts presented to the cows supply the required level and balance of nutrients in addition to water.

Impact of dry matter on diet formulation and feeding management
In most dairy diets, there are several ingredients (e.g., silages) that contain a large percentage of water. Often the dry matter percentages of these ingredients vary from location to location within storage sites (such as a silo or pile) and can be affected by exposure to precipitation.

For excellent feeding management, an accurate measurement of the current dry matter percentage of each ingredient is required for determining the correct actual (“as-fed”) amounts to mix and present to the cows. These feeding adjustments are especially crucial for ingredients that contain a lower percentage of dry matter.

Figure 1 and Table 1 show the pounds as-fed required to deliver 1 pound of dry matter over a range of dry matter percentages. Notice that the rate of change accelerates as the dry matter percentage drops below 40 percent.

pounds as-fed required to deliver 1 pound of dry matter over a range of dry matter percentages

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pounds as-fed required to deliver 1 pound of dry matter over a range of dry matter percentages

Small changes in dry matter percentages within wetter ingredients can have a major impact on the required as-fed amounts for these ingredients. If not properly recognized and accounted for, the overall diet can quickly become unbalanced. The result can be suboptimal production, poorer health and decreased reproductive fertility.

Limitations of methods of determining dry matter
The methods for determining dry matter percentages on dairies have typically been either cumbersome or time-consuming. These limitations have often led dairymen and their feeding crews to perform dry matter testing much less frequently than would be advantageous for excellent feeding management.

Devices using newer technology are becoming available and affordable to easily and accurately measure dry matter at a dairy’s feed center in less than a minute. Most of these devices utilize near-infrared (NIR). These devices have much promise to improve feeding management.

Economic considerations involving dry matter
Feed is typically priced and purchased on an as-fed basis. Water is usually much less expensive than the nutrients contained in the dry matter. Therefore, if there are two sources of the same ingredient at the same price that differ only on dry matter percentage (assuming the same quality and palatability otherwise), the source with the higher dry matter percentage has greater economic value.

While the adjustments required for feeding ingredients that are very dry (85-plus percent dry matter) are usually relatively minor, in many cases these ingredients are higher in price. Therefore, even though there may be little to no impact on supplying the nutrients required, there can be economic impact.

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As Table 2 illustrates, a drier ingredient priced at $400 per ton as-fed costs about $27 more per ton of dry matter as the dry matter percent decreases from 90 percent to 85 percent. At a feeding rate of 5 pounds per cow per day, this 5 percent difference is $0.07 per cow per day.

illustrates, a drier ingredient priced at $400 per ton as-fed costs about $27 more per ton of dry matter as the dry matter percent decreases from 90 percent to 85 percent

For wetter ingredients, as noted above, the rate of change accelerates as the ingredient becomes wetter. As an example, Table 3 shows a $29 difference per ton of dry matter for a feed purchased at $60 per ton as-fed. At a feeding rate of 10 pounds per cow per day, this 5 percent difference is $0.14 per cow per day.

shows a $29 difference per ton of dry matter for a feed purchased at $60 per ton as-fed.

Summary
Accurate determination of the current dry matter for all ingredients allows proper adjustment of the amounts presented to animals and has significant economic impact. Newer technology has the promise of allowing dry matter to be measured quickly, easily, accurately and affordably in a timely manner. PD

Steven Stewart is a veterinarian with Valley Ag Software, Tulare, California. His experience includes private dairy veterinary practice and teaching of continuing education to dairy consultants in a variety of topics.

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