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Constant Ration Density: the TMR Concept

Gordon Jones and Steve Stewart

Falls Animal Health Inc.,
Box 10,
Oconto Falls, WI, U.S.A. 54154
E-mail: 0006279938@MCIMAIL.COM

A dairy cow has two types of digestive mechanisms: 1) a microbial system to digest fibrous material, and 2) a chemical system similar to humans and swine. A productive, economically efficient, healthy cow must by definition have a healthy rumen. Therefore, we must feed the rumen microbes first and the pig behind the rumen secondarily. It is of little value to feed or be concerned about post-ruminal digestion if rumen microbes are under severe stress.

Rumen microbes function most efficiently in a narrow range of pH. A minimum amount of effective fiber must be present in the rumen to maintain microbial viability and numbers and avoid sudden pH drops. Hand-fed rations have an inherent tendency to be fed in "slugs", resulting in large amounts of starch being released in a short period of time, with a severe drop in pH and drastic reduction in microbial numbers.

The whole concept of total mixed rations (TMR) is each and every bite consumed by the cow has properly balanced levels of both fiber and other nutrients to maximize rumen and post-rumen digestion and improve digestibility of all ingredients. Less expensive ingredients can also be used; coupled with better efficiency of digestion, the result should be greater profitability for the dairyman.

It is often argued that hand-fed rations allow one to feed a cow "exactly" according to her needs. I feel, in most cases, we interfere with rumen digestion in early lactation with excessive grain and improper amounts of fiber, protein, bypass protein, etc. This leads to lower milk production, laminitis, and decreased dry matter intake (DMI). At this point we feed to production needs and at best maintain current levels and too seldom replace body condition for next lactation. These production losses are "hidden" and not immediately apparent. However, most people do know of someone who has achieved high milk production on hand-fed rations. These people have learned the art of feeding cows and observing cow behavior. Much effort must be expended in feeding multiple times per day and in feeding cows to their limits on grain without crossing a certain line.

This "art" is difficult to teach and difficult to learn. Worse, it is extremely labour-intensive, and as we move towards larger farms it becomes very cumbersome to give this individualized attention to each cow. Hence, we need systems where science can replace part of the art and where machines can replace part of the labour.

At one time computer feeders were gaining in popularity. At present, however, I feel this technology has a limited future for these reasons:

Feeds are limited to those of high palatability and easy handling. This severely limits feeding of economically and nutritionally superior commodity feeds such as whole cottonseed, wet brewers grains, meat and bone meal, etc. This usually results in rations of lower nutrient value at higher costs.
There is no built-in mechanism to weigh forages and no method to monitor forage intakes. Cows can still easily opt for excessive grain over forage resulting in health problems, or choose excessive forage over grain, limiting production.
Much management time and ability is required to adjust amounts of feed to individual animals.
The tendency is to improperly challenge early lactation cows and to underfeed late lactation cows for proper body condition.
The technology itself is expensive and subject to being quickly outdated, with replacement parts difficult to find.

The following tables illustrates the concept behind a TMR. Note in Table 1 that a cow who consumes 70% of the average total as fed intake also eats 70% of the average as fed intake of any single ingredient. See also Figure 1. Keep this figure in mind as it will be re-appearing many times under different guises.

In Table 2 a few nutrient parameters and costs are listed at various percentages of average intakes. Examine Figure 2. Note that Figures 1 and 2 are identical in nature. The point here is the same as that stressed in paper "Dry Matter Intake and Milk Production" in that one must define DMI before one can discuss absolute amounts of nutrients or costs in rations.

Next examine the numbers in Table 3. Note the following:

As production increases, energy levels with a TMR more nearly matches protein levels to maintain a given level of production. This is true due to the ability to make a ration more energy dense and avoid a negative energy balance at higher production levels. See Figure 3 for a pictorial representation.

In top-dressed rations the tendency is to feed the same amounts of forages across all levels of production. This leads to fiber levels becoming dangerously low at higher grain levels and a tendency to over feed protein, leading to both health and economic problems. At lower production levels, grain and protein levels are often reduced to levels where production and replenishment of body condition suffer.

Total mixed rations help avoid this by increasing forage at the same rate as other ingredients, thus preserving a minimum level of fiber in the diet. Digestibility should also be improved by avoiding the cyclic severe pH drop associated with grain feeding

Higher production - feed costs per litre of milk drops as production rises and percent return on investment also rises. With absolute amount of income and percent return rising with increased production, this situation is similar to asking whether one wants 5% interest on $100 or 6% interest on $110. See figures on following pages.

Higher production is more efficient because less of the total feed costs are directed to maintenance. Although the rate of change does slow, it still is a trend to greater efficiency no matter how high production rises. However, income is greatly increased due to increased volume. The conclusion I would draw is increased profitability can best be achieved by first maximizing efficiency through increased production/decreased feed cost per cow and then by increased numbers of cows.

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