Dry Matter Intakes and Balancing Diets
Most of us have had to balance a financial budget at one time or another. In the world of business, you know that expenses must not exceed income or you'll soon get a visit from the bill collector. We've all learned that by not having an accurate idea of how much money is coming in and when it's going back out - something called responsible fiscal management - operating a business can be a nightmare and is most likely doomed to failure. For dairy farmers, a foundational feature of sound fiscal management is knowing how much feed your cows consume every day of every year.
Dairy farmers feed a variety of feedstuffs to their cows and calves. Some of that feed is high in moisture, while some is not. Corn silage, for instance, is typically 70 percent water, leaving 30 percent as actual solid food material. So when you feed 70 pounds of corn silage to your milk cows, the actual amount that provides nutrition (such as protein, energy, vitamins and minerals) is 21 pounds; the rest is water. Dry hay, on the other hand, is about 10 percent moisture/water. When you feed a cow 10 pounds of hay, you're feeding her 9 pounds of what we call dry matter. Pasture grasses are about 80 percent moisture and 20 percent dry matter.
A high-producing milk cow that must consume 45 pounds of dry matter to meet her intake needs for the day, if out grazing on pasture, must consume 225 pounds of fresh herbage over the course of a day.
When someone tells me that they're feeding 100 pounds of feed to their cows, it really doesn't tell me anything that will help me balance a diet. I have to know what percentage of that diet is a high-moisture feed and what portion is low-moisture. When I balance a milk cow diet, I need to know how much dry matter we're really talking about. From there I can tell a farmer if the diet is supporting enough milk production and provide an accurate value of the cost of nutrients.
In order to balance milk cow diets accurately and cost-effectively, we must know a cow's feed consumption calculated as dry matter.
Even though water is essential in a cow's diet for metabolic function, we really don't care about the water from a purely nutritional standpoint - water offers no protein or calories. In some cases, though, excessive levels of dissolved minerals in water can impact the mineral balance in the diet.
Dairy cow diets that consist of high percentages of corn silage or haylage can be problematic when trying to nail down the accurate dry matter consumption in the herd. For instance, 80 pounds of corn silage that is deemed to be 30 percent dry matter will yield 24 pounds of dry matter. However, if the moisture determination is several percentage points off - say it's actually 34 percent dry matter - the dry matter in that 80 pounds of corn is really 27.2 pounds.
That's over 3 pounds of dry matter that's not being accounted for correctly in the diet. Maybe the cows really are eating that much silage, which means they're eating more than we think they are or possibly less of something else. Since the cows are consuming more corn silage, the protein level in the diet may not be adequate to support the desired level of milk production. Not knowing the correct dry matter in a feed can quickly result in an inaccurately formulated diet. Of course, it's generally the nutritionist's responsibility to make sure that dry matter values are correct by regularly taking samples of all high-moisture forages.
Do you know how many pounds of dry matter your cows consume every day? When you mix a TMR for 100 cows and the mixing sheet tells you that the total load should weigh 4,900 pounds for the morning feeding, is that what you end up with? Or do you tweak it a little and add another 100 pounds of feed? If so, which commodity are you overfilling the mix with? Since that thunderstorm came through during the night and dumped a half-inch of rain on the face of the silage pile, are you compensating for the extra moisture in the feed wagon this morning or just feeding the cows extra water?
As an example, a milk cow ration is formulated to support 70 pounds of milk, and the daily dry matter feed intake is expected to be 46.5 pounds. Corn silage consumption in this diet is expected to be 55 pounds as fed, or 16.8 pounds of dry matter at 30.6 percent dry matter. If, for some reason, the silage turns out to be 34.6 percent dry matter and the cows are actually eating the 55 pounds as fed, this amounts to about 2 more pounds of dry matter consumed by the cow.
Now, this is not necessarily a bad thing, as long as the cows are giving more milk. Adding 2 more pounds of corn silage dry matter should result in about 4 more pounds of milk. If they do not, then suddenly you're spending more on feed with no added milk revenue to cover it. Milk production relative to feed intake - feeding efficiency - begins to suffer, costing the business money.
That's not to say that the cows are wrong to be eating more feed. Perhaps the weather has cooled down from the summer humidity or there are more fresh cows in the herd that will affect overall dry matter consumption in a group. Many things can happen in a herd that will affect their feed intakes over the course of months or seasons. However, we need to be aware of the changes.
A four-point spread in moisture content in a 500-ton pile of silage amounts to 20 tons of dry matter. That 20 tons of dry matter may mean the difference between having enough feed to make it to the next crop or having to buy it from a neighbor. The point is to be aware of your herd's feed consumption. By knowing the dry matter content of all your feedstuffs, you will do a better job of balancing diets, producing milk and budgeting for your feeding program, and it will be easier to plan how many acres to plant and manage your feed inventory.
The author is a dairy nutritional consultant and works for Central Connecticut Cooperative Farmers Association in Manchester, Conn.