What is dry matter intake and why is it important for dairy farmers to understand?
Dry matter intake is the amount of feed a cow consumes per day on a moisture-free basis. Most producers are used to dealing with feed on an as-fed basis (Kgs of feed actually fed to animal with the water in it); however, in order to determine an accurate estimate of the nutrient intake and to compare feeds, an animal’s diet must be analyzed on a moisture-free basis. There are three major factors that can affect a ruminant animal’s dry matter intake: feed ration (the quality and availability of forage and the amount and type of supplements); the environment; and the animal itself (including size, body condition, stage of life and level of production).
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In reality, this is the level of intake that a cow must consume of a ration that contains the energy concentration recommended for her by nutrient tables.
It’s well known that consumption of less-digestible, low-energy, high-fiber diets is controlled by rumen fill and the feed passage rate through the animal. Meanwhile, consumption of highly digestible, high-energy, low-fiber feeds is controlled by the animal’s energy needs and by metabolic factors.
These concepts may seem quite simple, but the factors that regulate DMI are complex and aren’t fully understood.
How much dry matter will a cow eat? There’s no simple and exact answer, but we can predict DMI reasonably well from tables and practical experience.
Depending on the quality of the diet, a mature cow will usually consume 1-3% of her body weight (BW). Consumption of low-quality feeds may be 1-2% of BW, while green pasture may be 2-3%.
The factors that influence the amount a cow will eat include her size, body condition, stage and level of production. Other factors include the quality and availability of forage, amount and type of supplements and her environment.
With diets high in fiber, the rate and level of digestibility — and rate of passage of the feed — will have a large effect on intake. The faster the feed is digested, the faster it passes through the digestive tract and the more it allows for an increase in consumption. Poor-quality roughage such as straw, on the other hand, will have a slower rate of digestion than a high-quality feed such as alfalfa.
Feeding more dry matter than is required to meet an animal’s needs is a waste of feed. With high-quality alfalfa hay, the energy and protein requirements can be met with about 17.5 lbs. of hay. Since the rate of passage will be relatively fast, the cow may appear hungry before the next feeding, even though her nutrient requirements have been met.
With straw, the cow would have to eat about 44 lbs. to meet her energy and protein requirements. This she can’t do. We can predict that she would eat only 20 lbs. [1,000 lb. X 2% DMI (max.)].
The cow will appear full, but she won’t be meeting her nutrient requirements. It’s a scenario I see quite often in cattle on corn stalks or other poor quality roughage.
Factors affecting DMI
Implants tend to increase feed intake while Rumensin tends to decrease feed intake.
A protein deficiency (less than 6-8%) also may decrease feed intake. This often occurs when cattle are on corn stalks, straw or other low-quality roughage.
This explains why supplemental protein increases DMI, as well as the digestibility of the roughage. Protein is needed by the rumen bugs to multiply and digest fiber.
Palatability also may affect DMI. Highly palatable feeds encourage consumption, while bitter-tasting feeds, no matter the value, will limit consumption. Molasses-based supplements encourage dry matter consumption. They’re a good example of how we can manipulate DMI and, inherently dry matter digestibility, which increases rate of passage.
Not an exact science
Predicting DMI isn’t an exact science. But by understanding the factors that affect DMI and the tables to estimate levels, as well as some practical experience, we can become comfortable in using estimates.
One problem in estimating DMI from tables or published data using rumen fill or energy demand is the phenomena of large increases in DMI in certain situations. These would include during lactation, cold stress and shortly before an impending storm or low-pressure front advancing to an area.
In addition, decreases in DMI have been observed with advancing pregnancy just when there are increased nutrient demands on the cow.
5 steps to increase dairy cow dry matter intake
In dairy cattle nutrition, any possible increase in dry matter intake (nutrients) is associated with higher milk yield. In general, and assuming a well-balanced ration is offered, an increase in dry matter intake of 1 kg per day results in about 2 kg extra milk. However, increasing dry matter intake beyond daily voluntary intake is rather difficult. There are steps to be taken at the farm level, regarding animal and feed management, but there are aspects of this problem that can be addressed while designing a dairy nutrition program. Below are five steps to push dry matter intake upwards by nutrition intervention strategies during feed formulation.
1. Use forages of higher quality
Gut capacity has a physical limit, beyond which feed intake ceases. Thus, to increase nutrient intake within the limits of physical capacity, ingredients of the highest nutrient value must be used. As grains and fats cannot be used freely to increase nutrient intake (due to metabolic disorders), it is only through forage quality that we can maximize ration nutritive value. To this end, forages with a net energy value above 1.3 Mcal/Kg are essential to enhance dry matter and nutrient intake. Corn silage is rich in energy, whereas alfalfa is slightly above the required level. Other forage materials are either borderline or below the mark.
2. Avoid metabolic disorders
Cows suffering from metabolic disorders (acidosis, ketosis, milk fever, etc.) will respond to feed intake in the same manner as sick animals: they will invariably reduce their daily intake. Thus, it pays to take any and all measures to ensure lactating cows do not suffer from such disorders, which are usually prevented by proper diet design and feeding management.
3. Limit fat in fresh cows
Following calving, cows will invariably mobilize body fat to sustain milk production, regardless of feed availability and quality. This mobilized fat increases circulation of non-esterified fatty acids, the same way as adding extra fats in the feed. The physiological response of cattle to such elevated amounts of fat catabolism components is to decrease feed intake. If the ration contains added fat, then fresh cows will respond by reducing feed intake, as they cannot stop body fat mobilization. This is particularly important in first parity cows.
4. Condition cows pre-calving
Peak milk yield proceeds peak dry matter intake by at least 5 to 10 weeks. This means early lactation is supported by body fat reserves, as dry matter intake cannot match requirements. To reduce the amount of body fat mobilization and enhance dry matter intake in fresh cows, pre-calving conditioning is recommended. This is achieved by using a transition diet about three weeks before calving. Such diet should be rich in fermentable carbohydrates to stimulate rumen absorptive capacity and increase rumen volume. It also helps reduce the incidence of ketosis at calving, which also affects dry matter intake.
5. Use additives that balance rumen functioning
There are not many additives that work predictably in conditioning rumen functionality. This is because each additive depends on the conditions created by the total ration consumed by the cow and her physical and health condition. Thus, each additive must be evaluated on a farm-specific approach. In general, sodium bicarbonate, yeast and yeast derivatives are the most commonly used additives. Others, less frequently used include enzymes, probiotics, clays, algae and different salts. It should be noted that the use of additives is secondary to balancing the ration. Additives should be used to enhance dry matter intake and not fix problems created by improper ration design.
Presumably, an attending nutritionist already takes care of the above issues, but quite often, for cost saving reasons, some corners are cut. Such is the case when feedstuffs become extremely expensive. But, care should be taken to return to maximal milk yield potential when such exercise becomes again profitable. Modern dairy cows have a tremendous capacity for milk yield, and it is to our benefit to provide them with the best possible nutrition to ensure they express their full genetic potential.
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