Dr. Don Llewellyn
Livestock Extension Specialist
Director, WSU Lincoln County Extension, Davenport, WA
Myth: It makes no difference if one calculates cow feed intake on a dry matter basis or an as-fed basis.
Answer: Oh, but it does matter!
Okay, here we go! This is one of those topics that probably caused more confusion among my students than most any question I asked them (or had them calculate on an exam!). Let’s make some practical sense of this and how it applies to the real world for cattle producers.
Before we can address this concept, we define our terms: As-is (or as-fed) basis refers to selling or using feed with no adjustments made for moisture content. On the other hand, feed sold or used with adjustments made to account for variation in moisture content is referred to as dry-matter basis. So why does this really matter? Two reasons come to mind that we need to address here: 1) when calculating projected intake, we do so on a dry matter basis and 2) it is also important when determining if the cows’ nutritional requirements are being met.
Being able to systematically figure out how much a cow will eat is useful in determining how much hay or other commodities will be needed for winter feeding. Table 1 provides some ‘rules of thumb’ for dry matter intake of nonlactating, pregnant cows in the winter:
|Feed quality||Estimated intake (% BW)|
|Low-quality forages (< 7% crude protein)||1.5|
|Moderate quality hay (8 – 10+% crude protein)||2.0|
|High quality hays, silages, and pastures||2.5|
For example, a 1,350 lb. cow that is eating hay or other forage in the low-quality category would be expected to eat 1.5% of her body weight. That is: 1,350 lbs. x 0.015 = 20.25 lbs. of hay per day on a dry matter basis. Then, an adjustment is necessary for the actual dry matter of your feed which you can find on your forage analysis lab results, or you can determine yourself (your WSU Extension professional can show you how to accomplish this safely; without setting the kitchen on fire). To make the adjustment: The cow is projected to eat 20.25 lbs. of dry matter so we simply divide by the dry matter content of the hay (in this case, let’s say the hay is 10% moisture which is 90% dry matter). 20.25 ÷ 0.90 = 22.5 lbs. of hay on an as-fed basis. From this calculation it is expected that the daily intake will be about 22.5 lbs. per cow per day. Intake changes a bit with stage of pregnancy, but this will get you all in the ballpark in calculating your needs for winter feed stocks. This amount doesn’t consider waste in the feeding process, and producers will need to make an educated guess as to what the waste might be and adjust the as-fed amount accordingly. Producers can use this calculation for yearlings on harvested feed, pasture, and stockpiled feed as well.
Next let’s look at how this whole as-fed/dry matter issue affects how cattle perform and meet their nutritional requirements. Let’s say some 800 lb. yearlings are grazing some very immature (early vegetative stage) grass pasture. The grass is 20% dry matter (80% moisture) and we expect them to eat 2.5% of BW in dry matter. That is: 800 lbs. x 0.025 = 20.0 lbs. of dry matter. Then we convert that to asfed by dividing by the dry matter %, 20.0 ÷ 0.20 = 100 lbs. of feed on an as-fed basis.
Uh oh, what’s happening here is that the animal is going to be full before they can consume their expected amount of dry matter. It is conceivable that the animals provided extremely wet feeds or pastures may not be able to eat enough to meet their requirements for energy. As nutritionists, we see this in stocker cattle on high-quality wheat pasture in the Midwest and they still require supplementation to meet their nutrient requirements. Recently with interest growing in Eastern Washington for using canola or other Brassicas for grazing, as well as grazing cover crops, this will become a more prevalent issue that will need to be considered in how the cattle are managed to ensure adequate dry matter in the diet.
There you have it; the myth is busted! It is important to project intake on a dry matter basis and convert to as-fed in determining feed needs for the cow herd. Special care must be taken to ensure that nutrient requirements are being met when utilizing very wet feed.
Please let me know if I can assist you with your cattle feeding programs. If you have an idea for a myth for a future Beef Cattle Mythbuster column, I would be happy to hear from you on that topic as well. Don Llewellyn, 509-725-4171, firstname.lastname@example.org