Feeding a total mixed ration (TMR) ideally results in rumen bacteria encountering the same mixture of ingredients and nutrients in the cow's rumen throughout the day, a consistency that helps improve fermentation. It may also result in better intake by the cow herself and improve her milk production, health, and reproductive performance. But, as with any fine-tuned machine, minor inconsistencies and improperly followed guidelines in the use of TMR can decrease milk production and increase health problems. Premature culling or even death of cows may result, depending on the severity of the response.
When feeding a TMR, it is important to monitor:
The dry matter content of silages and wet byproducts should be monitored at least twice monthly, preferably weekly. The dry matter content of feedstuffs stored in a bunker silo should also be determined, especially after half an inch of rain has fallen, because a change in the dry matter content of these feeds can greatly affect the nutrient content of the mix being fed and may result in lower milk production or increased health problems.
When nutritionists balance rations for dairy cattle, they assume that the cow will receive a certain amount of dry matter from a particular feed. As the feed becomes wetter, more of the feed needs to be included in the TMR in order to provide the same amount of dry matter to the cows and keep nutrients in their correct proportions. The reverse is also true: as feeds become drier, less of the forage or feed needs to be included. Nutritionists often include a table along with their balanced rations to help the farmer adjust the amount of forage or wet byproduct to be added to the TMR as the dry matter content of feeds changes.
In order to manage the feed bunk effectively, a daily log should be kept that shows, for each feeding, how much feed was fed and how much feed was left in the feed bunk from the previous feeding. This log becomes extremely important when more than one person is feeding the cows, as when the normal feeder is absent unexpectedly. With a daily log, each feeder can quickly and accurately determine what other people have fed and can adjust the amount of feed accordingly. The nutritionist can also use this information to make sure that the ration is as economical as possible, cows are actually consuming the expected amount of dry matter or feed, and potential problems are noted before they affect performance and the dairy operation's profitability. Table 1 shows a sample worksheet that can be used to record feed intakes and refusals.
Milking cows need quality feed available 20 hours of a day, so the TMR should be located within 100 to 300 feet of their freestalls or resting place. Feed should be pushed up in front of the cows to stimulate them to come up and eat additional feed. Cows should be fed so that 5 percent of the offered feed is left when they are fed the next time. From a practical standpoint, this means that approximately an inch of feed should be left in the feed bunk at the next feeding, and leftover feed should be removed routinely.
When increasing or decreasing the amount of TMR fed, the amounts of each forage, grain, and each of the other ingredients need to be increased in proportion to the originally formulated TMR. Do not simply feed cows more forage if they clean up feed from the previous feedings.
One of the most common misperceptions when increasing or decreasing the amount of TMR offered is to change the amount of forage offered while holding constant the amount of grains and other concentrates fed per cow. This change results in a misbalanced ration that can decrease milk production or result in health problems in the cows. One way many farmers adjust the amount of each ingredient in the TMR is to feed their cows as if the group has been expanded by two to five cows or been reduced by two to five cows.
Cows need to consume adequate amounts of long forages or fiber in their TMR so that they can regurgitate the feed, chew their cud, and secrete saliva, which helps buffer the rumen environment so that the bacteria can efficiently digest forages. Studies show that cows chewing their cud may secrete 5 to 6 pounds of saliva daily. When nutritionists balance rations for dairy cows, they try to provide adequate amounts of effective fiber, or "chew factor," so that enough longer particles are present in the rumen to stimulate cud chewing.
When a TMR mix is overmixed, the particle size of the forages decreases. This, in turn, decreases cud chewing time and saliva production, which may lead to an increased incidence of problems such as ruminal acidosis, laminitis (foot problems), displaced abomasum (twisted stomach), decreased feed intake, decreased butterfat, decreased body condition (which may decrease ability to breed), and in severe cases, death. Generally, most models of TMR mixers need only three to six minutes of mixing time.
The particle size of the TMR should be evaluated using a Penn State particle separator box (see Figure 1). This separator box consists of three separate boxes that allow the TMR mixture to be separated into three particle sizes. These results should then be compared to what is expected for a TMR. Expected percentages retained on each of the three boxes are shown in Table 2. Most nutritional consultants have particle separator boxes available, or farmers can purchase one from suppliers such as Nasco. At a minimum, particle size should be determined when forage type and crop year change, a new mixer is purchased, or augers or knives are repaired or sharpened.
|Generally, TMRs should be mixed from 3 to 6 minutes per load. Do not overmix or run the PTO for long periods of time when loading wet feeds.|
To make sure that the TMR mixer is functioning adequately and consistently, samples of newly delivered feed should be collected at several different locations in the feed bunk. For example, samples should be collected at the beginning, middle, and end of the feed delivery sequence. These results then need to be compared to one another to detect any potential problems.
Feed not consumed should also be evaluated. This evaluation helps diagnose any problems of excessive sorting behavior in cows. This diagnosis becomes extremely important when greater than 7 pounds of hay per cow is fed daily through a TMR and large amounts of cobs are left in the feed bunk. Even when a balanced ration is mixed properly, sorting of larger forage particles can lead to problems due to imbalances and lack of effective fiber for cud chewing that can result.
|Forage or Feed||Box Location|
|Corn Silage (3/8 in. TLC and unprocessed)||2-10%||> 50%||< 50%|
|Corn Silage (3/4 in. TLC and processed)||10-20%||50-60%||< 30%|
|Source:Adapted from Penn State and University of Illinois recommendations. Note:TLC is theoretical length of chop. Processed corn silage refers to corn silage chopped with a kernel processor on the chopper.|
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Donna M. Amaral-Phillips
José R. Bicudo
Larry W. Turner