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Dry Matter Intake and Milk Production

Gordon Jones and Steve Stewart

Falls Animal Health Inc.,
Box 10,
Oconto Falls, WI, U.S.A. 54154
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Central to any discussion of dairy nutrition is a full grasp of the concept of dry matter intake (DMI). Dry matter intake is calculated by measuring the quantity of total feed intake per animal per day on a moisture-free basis. Several physiologic and management factors impact level of DMI and will be discussed later in more detail. However, one must be aware that DMI both drives milk production and is driven by milk production; i.e., the higher the DMI the higher the milk production and the higher the milk production the higher the DMI.

How is DMI determined? One method is to use prediction equations based on several factors including size of animals, level of production of milk and solids, breed, etc. There are many such equations available. The output from one program (University of Wisconsin Extension) is shown in Figure 1. The major problem, however, with these predictive equations is that one cannot automatically assume these DMI's are actually occurring on the farm.

Therefore, although these prediction equations can be useful as a starting place for ration calculation, ultimately rations succeed or fail on the basis of actual DMI consumed, not on what DMI is assumed to be. All quantities of all feedstuffs consumed, not just presented, must be measured. This is difficult if not impossible to do when rations are hand-fed ("top-dressed") where the cows are able to pick one feedstuff over another or otherwise sort ingredients. Seldom also are quantities of feedstuffs weighed with any regularity or accuracy. Hence, total mixed rations (TMRs) offer advantages here in not allowing sorting or preferential consumption of feedstuffs and in allowing regular weighing of all ingredients.

Daily Requirements

Once the idea of DMI is understood, the next concept is nutrient requirements of dairy cattle. The authoritative source of requirements is the NRC publication. The levels listed in this book, modified by experience and university research results, serve as an excellent starting place. The main idea here is to remember animals do not have a density (percentage or ppm) requirement; they have an absolute requirement of kilograms, grams, milligrams, etc. Many errors in ration formulation occur at this level. Note Tables 1 and 2.

Table 1 illustrates very well the importance of DMI. At a ration CP density of 19.0% of DMI at 25 kg will support 49 kg of milk while a DMI of 20 kg will support 39 kg of milk per day. It is meaningless to ask "what level of milk production is a ration balanced for?" without also defining level of DMI. Errors occur here when DMI is assumed to be higher than actual. Ration is called "balanced", but performance is lower than expected, often tempting one to try "secret" or special" ingredients at great costs and little results. Here the actual DMI must be measured and either increased (ideal) or, as is illustrated in Table 2, density of nutrients increased.

However, there are upper limits on nutrient densities above which performance starts to decrease rather than increase. Therefore, often one must try to increase DMI if one wants to increase performance. However, again, do not simply plug in a higher number for DMI into the computer and be pleased how easily the ration "balances"; the cows have to actually eat the higher DMI.

My personal approach however is a little different: I try to balance a high group ration for approximately 19% CP, 40% non-fibrous carbohydrates, 6 to 7% total fat and neutral detergent fiber from forage (NDF-F) at 21 to 23% (depend on forage source and "effective" fiber). Therefore, I tend not to change ration densities from one high group to another based on production, but rely instead on proper selection of cows to go into the group. At this point, I then attempt to maximize DMI. Attached is a copy of what I personally use do not accept these verbatim, but instead use them to help develop your own.

Methods to Increase DMI with Total Mixed Rations
Feed only highly palatable forages of optimal ADF and NDF levels. Alfalfa hays and haylages probably should test 28 to 32% ADF and 38 to 42% NDF for highest intake potential, digestibility, and palatability.
Feed TMR at least twice daily in winter and three to four times in the summer. Fresh feed should be available 20 hours a day.
Keep cows healthy, cool, and comfortable.
Allow unlimited access to cool, clean water.
Be sure bunk space is not limited so intake is ad lib.
Clean bunks to measure weigh-back and also to decrease secondary fermentation from occurring.
Be sure TMR is thoroughly mixed so no sorting can occur.
Separate the first calf heifers from the older cows.

Higher milk production must be compensated over the long run by higher DMI. There is no such thing as a free lunch. The goal of every dairyman should be to maximize DMI in all production groups.

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