Dairy cows require amounts (pounds or kilograms) of nutrients, not percentages. We usually talk about and balance rations for percentages of nutrients (i.e. 17% CP and 0.90% Calcium). But, we must recognize that dairy cows require certain amounts of protein, energy, and minerals to support different levels of milk production. To determine if the diet will support the desired milk production, the percentages must be converted to actual amounts (pounds or kilograms). One researcher estimated that 50-70% of the variation in nutrient absorption between cows is accounted for by differences in dry matter intake.
Required nutrients must be provided within an amount of dry matter that the cow can really eat. Normally, when we balance rations for percentages, we make an assumption as to what the dry matter intake will be. This assumption is based on an understanding of appetite controls (feeds, animal, management, and environment). Usually computerized feeding programs will use equations based on a number of appetite control factors to make intake predictions for various levels of milk production. It is always a good idea to verify intake assumptions for groups of animals on a farm.
Example: A cow weighing 1300 pounds (590 kg) and producing 80 pounds (36 kg) of milk per day containing 3.5% milk fat requires 7.6 pounds (3.45 kg) of protein, 34.4 Mcal of NEl, and 150 grams of calcium.
| Expected Dry Matter Intake (pounds) |
43 |
45 |
47 |
| Crude Protein (%) |
17.7 |
16.9 |
16.2 |
| NEl (Mcal/lb) |
0.80 |
0.76 |
0.73 |
| Calcium (%) |
0.77 |
0.73 |
0.70 |
* Adapted from Chase and Sniffen
Maximizing dry matter intake permits high levels of production to be supported at a lower feed cost per unit of milk produced. The more nutrient dense a feed or ration is, the more expensive it is. As the above example shows, increasing dry matter intake reduces required ration nutrient density, allowing one to include more inexpensive forage and fibrous byproducts and less grain (normally expensive) in a ration.
Less nutrient dense rations consumed at high levels of intake normally promote greater rumen health and productivity. Dairy cows were designed to ferment forage, chew their cud, and maintain a healthy rumen microbial population. As we raise the amount of grain increasing ration NFC levels, there is greater risk of sub-clinical acidosis. This reduces the growth of the rumen bacteria, especially the fiber-fermenters, reduces digestibility of the ration, and further reduces intake.
What Controls Dry Matter Intake?
1. Physical Capacity of the Digestive Tract
There is a limit to how much material can be stuffed into a cow’s rumen. Cows will stop eating when they feel full. Rumen size is a function of total body weight, body size, body shape, internal body fat, and whether or not the cow is carrying a calf. Mature cows are usually expected to eat more than first-calf heifers. Physical capacity is generally thought to primarily limit intake in early lactation high-producing cows having high nutrient requirements.
Often, dairy farmers become frustrated when cows consume less forage than they think they should. Usually this problem is most apparent after a good growing season that has yielded a lot of high fiber, low digestibility forage. High-producing cows with a well-functioning rumen are limited in forage intake by the bulkiness of the fiber that fills up the rumen. High fiber forages, especially those with a slow rate of digestion, pass out of the rumen slowly. The longer particles sit in the rumen, the longer the cow feels full, and intake is reduced. Ration bulk is normally estimated based on NDF content and NDF digestibility.
The NDF Content of a feed or forage is the cell wall or fiber content. This is the bulky portion which is broken down by the rumen microbes and which cannot be broken down by the cow’s own enzymes. Researchers at Cornell in the 1970’s (Mertens and Van Soest) compared the forage intake of sheep with the forage’s cell wall content. They found that as the cell wall content of the forages increased, intake declined. The correlation between cell wall content and intake was –0.76. Mertens later developed the NDF-Energy Intake System using NDF as an estimate of the filling effect of forage and as an estimator of the energy content of forage. As forage NDF content increases, less forage can be in a ration and grain must increase. Generally, rations should not exceed a maximum level of NDF (NDF amount about 1.2% of body weight) otherwise intake will be compromised.
Typical rations designed for high production and maximum forage utilization will contain 21-24% NDF from forages with total ration NDF at 28-32%.
More recent Michigan State University work confirms that NDF limits intake. Twelve early lactation cows (13 DIM) were fed diets containing 83% alfalfa silage and 12% cornmeal. One diet contained 36.7% NDF and the other contained 34.9% NDF. Dry matter intake was less for the cows fed the higher NDF diet (42.68 vs. 44.88 pounds/day (19.4 vs. 20.4 kg/day)) and milk production was less for cows fed the higher NDF diet. But, the amount of NDF actually consumed was the same regardless of the percent NDF in the diet. Both groups consumed 15.62 kg/day (7.1 kg/day) of NDF. Thus, cows were limited in intake according to the amount (not percent) of NDF consumed.
NDF Digestibility also impacts the bulkiness and intake of a ration. NDF digestibility can range from 35-75% for forages. Increasing ration NDF digestibility can increase intake. Feed and forage that is more quickly broken down by the rumen microbes reduces the amount of time the rumen feels full. Of course, forages that are more digestible also have a higher energy value for the cow. Michigan State University researchers analyzed data from 13 sets of forage comparisons in the literature. They found that a one unit increase in NDF digestibility resulted in 0.37 pounds (0.17 kg) greater dry matter intake and 0.55 pounds (0.25 kg) more milk (4% FCM).
Other factors affect the rate at which a ration passes out of the rumen and the amount of time per day that a cow feels full. Intake may increase by grinding or pelleting fibrous feeds. Grinding increases density, increases the amount of surface the rumen microbes can attach to, and reduces the amount of rumination to be done on the feed. The downsides of grinding are that it may reduce rumination enough to cause acidosis and it may reduce fiber digestibility because the feed passes out of the rumen before the rumen microbes have a chance to digest it. A deficiency of rumen degradable protein can reduce the growth of the rumen microbes, reducing rate of digestion and intake. Sub-clinical rumen acidosis caused by high levels of fermentable starch or low levels of effective fiber and low buffer production can reduce fiber digestibility enough to significantly reduce total dry matter intake. Too little rumen fermentable starch may also limit the growth of fiber digesting bacteria and limit fiber digestibility.
Feeding management can impact the amount of time during the day that the rumen feels full. The goal is to have cows eat many small meals (10-12 meals) per day. Researchers have found that cows spend about 5 hours per day eating.
- Is fresh feed available 24 hours per day? Fresh feed should look, smell, and feel just like when it was offered. Corn cobs and heated silage don’t pass! Try to have 5% of the feed offered left as refusals.
- Do refusals look like the TMR that was fed? Cows should stop eating because they are full, not because the feed is unpalatable.
- Is feed fed more than once per day? (Many farmers get by with once/day feeding but most nutritionists would agree that more offerings/day is better)
- Is feed swept up to cows many times per day?
- Are social interactions causing cows to “slug feed” (eat less than 10-12 meals per day)? In one study, first-calf heifers spent 10-15% more time eating when they were in a separate pen from mature cows. Milk production was also 5-10% higher.
- Do cows want to walk to and stand at the bunk? If the floor is slippery, they are less apt to want to walk on it. Some farmers have installed rubber mats at the bunk to encourage cows to stand and eat longer.
- Is the freshest feed available right after cows are milked?
- Do cows have at least 18 inches (46 cm) of bunk space available?
- Is hay or long forage fed before grain in order to minimize fluctuations in rumen pH throughout the day?
2. Chemostatic or Physiological Regulation of Intake
End-products of digestion, such as volatile fatty acids, inform the cow’s brain (satiety center) of the cow’s energy status. The cow’s goal is to maintain a state of energy equilibrium. Intake is “turned off” by this mechanism, sometimes when the cow is not limited in intake by the physical capacity of the digestive tract (feeling “full”). As the amount of concentrate (grain) in the diet increases, eating is more apt to stop because of chemostatic factors rather than physical factors. Cows experiencing periods of high rumen volatile fatty acid production and high rumen acidity (pH<6) will stop eating sooner. This is often why you may see grain left in front of high-producing cows in a tie-stall barn. Causes of rumen acidosis include: low levels of effective (chewable) fiber in the diet, excessive levels of non-fiber carbohydrate (NFC) (>40%), too much rapidly fermentable NFC, inadequate amounts of added buffers such as sodium bicarbonate, slug feeding (not enough meals throughout the day), and ration sorting (cows picking out the grain and leaving the fiber)
The Ration Balancing Act:
|
Increase pH With effective Fiber: |
|
Decrease pH
With Non-Fiber Carbohydrates: |
- May Reduce Intake Because of Physical Fill Limitations
- Lower in Energy
- Yields Saliva & Raises Rumen pH
- Economical
|
|
- May Reduce Intake Because of Acid production
- Higher in Energy for Milk Production
- Increases Microbial Protein for Milk
|
| Goals of the Ration Balancing Act: |
- To provide enough effective fiber to produce saliva and buffer the rumen.
- To maintain an even and limited acid production in the rumen.
- To maximize forage utilization without limiting total intake because of physical constraints.
- To provide enough energy and protein to maximize milk production.
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3. Miscellaneous Factors Affecting Intake
Many other small factors can impact the amount a cow eats in a day. First, one must not forget “cow psychology”. Problems with dominant versus submissive cows exist in pen situations and can significantly impact intake, especially when moving cows between groups. For this reason, it is recommended that groups of cows be moved at one time rather than as individuals. Bunk space should also be adequate (at least 18 inches/cow (46 cm). Second, cows like consistency. Intake can be reduced by variable feeding schedules and ration changes. Third, wet rations have been found to reduce intake. The key intake depressor is not the water itself but the ammonia, amines, and unidentified compounds that are solubilized in silage water. For this reason, it is recommended that rations not contain more than 50% moisture, unless some of that water is from unfermented sources. Fourth, inadequate water intake (caused by poor availability or quality) can reduce dry matter intake. Studies in England found that decreasing water intake by 40% caused a 16-24% depression in dry matter intake. It is recommended that water intake by cows be monitored. Fifth, moldy feeds, especially those containing mycotoxins, can reduce intakes because of palatability as well as rumen upset. Sixth, excessive body reserves can depress intake, especially during early lactation. In one study, it took fat cows five weeks longer to reach maximum intake after freshening than thin cows (9.25 vs. 14.5 weeks). Excessive conditioning promotes the mobilization of fat and an increase in non-esterified fatty acids (NEFA’s) in the blood stream. This may cause the satiety center to more rapidly stop intake after the beginning of a meal. Seventh, heat stress will reduce intake. Finally, excessive levels of minerals in a ration will reduce intake.
How Much Dry Matter Intake (DMI) Can Be Expected?
As previously shown, many factors can affect dry matter intake. Because intake is in large part limited by the capacity of the cow’s digestive tract, milking cows will generally eat an amount equal to 3.5 – 4.5% of their body weight each day. For example, a cow weighing 1300 pounds (590 kg) would be expected to eat 45 – 58.5 pounds (20.5 – 26.5 kg) of dry matter per day. But, this is a huge range considering the impact it has on the concentration of nutrients needed in the ration and the cost of the ration. Therefore, dry matter intake equations that take into account more factors besides body weight, are generally used for the development of rations using computerized feeding programs.
Because intake is also regulated by physiological mechanisms, milk production is another important factor that drives a cow’s intake. A common equation used to predict intake based on milk production and body weight is:
DMI (lbs) = (0.0185 x Body Weight (lbs) ) + ( 0.305 x 4% Fat-Corrected Milk (lbs))
Note: [4% Fat-Corrected Milk = (0.4 x Milk (lbs) + (15 x (Fat % / 100 x Milk, lbs))
Ration balancing programs have more complex equations that include variables such as, days in milk (DIM), breed, body condition, feed additives, seasonal effects, environmental factors, and ration NDF concentration.
Predicting Dry Matter Intake for the Purpose of Developing a Ration:
When developing a ration and making a dry matter intake prediction, it is important to do all of your homework first. Forages should be analyzed, most importantly for NDF content. It is also advantageous to analyze for NDF digestibility. For each group of cows that rations are being developed for, determine current production of milk and milk components, evaluate the current ration being fed, and evaluate cow condition (manure, body condition score, peak milk production, persistency of milk production, and reproduction). From the evaluation, one should determine the level of milk production and milk components to shoot for when balancing the ration and understand the past problems, such as, inadequate ration energy, acidosis, or amino acid deficiency, that need to be corrected.
Determine the amount of Dry Matter Intake that the average cow in the group can consume based cow descriptions and ration parameters. Use the equations previously described or equations incorporated into a computerized ration program.
Determine the amount of Forage NDF that the average cow in a group should consume. This will be driven both by the minimum amount needed to maintain rumen health (generally expressed as a percentage) and the maximum amount that the cow can be expected to consume (generally expressed in an amount (pounds or kg)).
According to the NRC (1989), the minimum Forage NDF for a high-producing cow to avoid acidosis is19% of the ration. This minimum may not be appropriate unless many of the following apply: long forage particles, low NDF digestibility, high fiber byproducts, total mixed ration (TMR), adequate buffers, added fat, and a desire to minimize of forage intake. Most rations developed in the northeastern U.S. would have a minimum Forage NDF level of 21% or higher because of the use of highly digestible forages, few fibrous byproducts, and fermented forages containing limited particle size.
High fiber digestibility, maximization of roughage intake, rapidly degradable starches in the ration, slug feeding, and variation in forage dry matter and quality necessitate feeding higher amounts of Forage NDF. Mertens estimated that the maximum amount of NDF that a cow could consume is 1.2% of a body weight. If we assume that 75% of ration NDF is forage, then the average cow can consume 0.9% of her body weight in the form of Forage NDF. For example, a cow weighing 1300 pounds could be expected to consume 11.7 pounds (1300 x 0.009) of Forage NDF per day. Again, this maximum will vary (higher or lower) depending on fiber digestibility and feeding management.
Computing Daily Dry Matter Intake on the Farm:
Most nutritionists rely on equations in their computerized feeding programs to make initial predictions of intake for various groups of animals. But, once rations are implemented, it is best to follow up and find out how close the computer’s predictions are to reality. Because of the importance of maximizing and accurately knowing dry matter intake and because of the many factors that impact dry matter intake, it is best to develop a dry matter intake monitoring system for individual farms.
1. Weigh the total amount of feed and forage (as-fed) offered and refused daily. This is relatively easy with a mixer wagon, providing the scales on the wagon are accurate. Test scales using a 50 pound bag of feed (or other known weight) on each corner of the wagon or following manufacturers calibration recommendations. With a little work and ingenuity, you can also get an idea of what cows are eating even if they aren’t fed with a mixer wagon. Weigh the amount of grain per scoop. Weigh the amount of silage in a cart or fork-full and divide by the number of cows it is fed to. Weigh bales of hay and divide by the number of cows it is fed to. You may even want to time the amount of silage coming out of the silo via an unloader and multiply by the measured weight coming out per minute.
2. Use a moisture tester or microwave oven to determine the dry matter of forages. Depending on the feed storage situation, the needed frequency for moisture testing will vary. It is a good idea to at least do it on a weekly basis.
3. Know how many cows are in each group that you are feeding. (Believe it or not, sometimes this isn’t easy to find out!). Divide the total amount fed minus the total amount refused by the number of cows in the pen to determine the as-fed amount consumed.
4. Calculate dry matter intake
Example Dry Matter Intake Calculation
| Feed |
Pounds As-Fed % |
Dry Matter |
Pounds Dry Matter |
| Corn Silage |
20 |
0.35 |
7 |
| Haylage |
35 |
0.45 |
15.75 |
| Grain |
13 |
0.90 |
11.70 |
| High-Moisture Corn |
20 |
0.75 |
15 |
| TOTAL |
88 |
----- |
49.45 |
5. Plot and analyze dry matter intake. This helps in analyzing the impact of various feeding and management changes on dry matter intake. Also, if daily dry matter intake fluctuates significantly, it may indicate rumen health problems, such as acidosis.
References:
Allen, M. and M. Oba. 1996. Increasing fiber digestibility may increase energy density, dry matter intake. Feedstuffs. November 18, 1996. p. 12.
Allen, M. and M. Oba. 1996. Increase in fiber digestibility may boost energy density, dry matter intake. Feedstuffs. December 16, 1996. p. 14.
Chase, L.E. and C.J. Sniffen. Dry Matter Intake in Dairy Cattle Nutrition. Animal Science Mimeo. Cornell University.
Dado, R.G. and M.S. Allen. 1992. The seven eating habits of highly effective cows. MSU Animal Science Newsletter. September, 1992.
Dado, R.G. and M.S. Allen. 1996. Enhanced intake and production of cows offered ensiled alfalfa with higher neutral detergent fiber digestibility. J. Dairy Sci. 79:418.
Garnsworthy, P.C. and J.H. Topps. 1982. The effect of body condition of dairy cows at calving on their food intake and performance when given complete diets. Anim. Prod. 38:181.
Mertens, D.R. 1985. Factors influencing feed intake in lactating cows: from theory to application using neutral detergent fiber. Page 1 in Proceedings of the Georgia Nutrition Conference, Atlanta
Mertens, D.R. 1987. Predicting intake and digestibility using mathematical models of ruminal function. J. Animal Sci. 64:1548.
Oba, M. and M.S. Allen. 1999. Evaluation of the importance of the digestibility of neutral detergent fiber from forage: Effects on dry matter intake and milk yield of dairy cows. J. Dairy Sci. 82:589.
National Research Council. 1989. Nutrient Requirements for Dairy Cattle. 6th rev. ed. Update 1989. Natl. Acad. Sci., Washington, DC.
Nocek, J.E. and J.B. Russell. 1988. Protein and energy as an integrated system. Relationship of ruminal protein and carbohydrate availability to microbial synthesis and milk production. J. Dairy Sci. 71:2070.
Roseler, D.K., D.G. Fox, L.E. Chase, and W.C. Stone. 1993. Feed intake prediction and diagnosis in dairy cows. Page 216 in Proceedings of the Cornell Nutrition Conference for Feed Manufacturers, Rochester, NY.
Sniffen, C.J., R.W. Beverly, C.S. Mooney, M.B. Roe, A.L. Skidmore, and J.R. Black. 1993. Nutrient requirements versus supply in the dairy cow: Strategies to account of variability. J. Dairy Sci. 76:3160.
Van Soest, P.J. 1982. Nutritional ecology of the ruminant. O&B Books, Inc., Corvallis, OR.
Related Links:
Maximizing Feed Intake for Maximum Milk Production
Rick Grant, University of Nebraska - Lincoln
Managing Dairy Cattle for Cow Comfort and Maximum Intake
Rick Grant and Jeff Keown, University of Nebraska – Lincoln
Ration Formulation In: Feeding the Dairy Herd North Central Regional Extension Publication
J.G. Linn et al.
Greater Cow Productivity Through Feed Bunk Management
H.T. Ballantine
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