September 5, 2017 at 3:32 p.m.
Where's the forage?
Forage quality and digestibility are important factors in keeping the cost of feeding dairy cows low and milk production high. Forages provide both structural (physical) and chemical neutral detergent fiber (NDF) in dairy cow diets. The structural NDF is important for cud chewing and good rumen health while digestibility of the chemical NDF provides energy for milk and milk fat production. As we approach the next several months of limited forage feeding, I thought it would be good to review some guidelines on balancing for and feeding NDF in lactating cow diets.
Forage, percent of diet dry matter (DM)
In Midwest lactation diets, forages usually exceed 50 percent of the total diet DM contributing to low feed cost and profitable milk production. To achieve this, forages have to be high quality. However, this is the year to put forage quantity slightly ahead of quality in forage production. I am not suggesting 100 RFV hay (haylage), road ditch hay or straw when I say quality is second to quantity, but this is not the year for 175 to 200 RFV haylage. A target of 140 to 150 RFV haylage for feeding will provide both quantity and quality. With haylages or hay above 175 RFV, cows require and eat more of this forage to meet fiber requirements. For example, 1 lb. of straw with an NDF of 76 percent can substitute for 2.25 lb of 190 RFV hay with an NDF of 34 percent. When straw is substituted for hay, there is a void of 1.25 lb that another lower cost or more available feed can fill. Corn silage will be a good alternative to fill the space this fall, however high fiber by-product feeds will be a strong consideration to fill the forage space this summer.
Total NDF, percent of DM
The general recommendation is 28 percent NDF in the diet DM with 75 percent of the total NDF coming from forages with good effective (physical) fiber. However, the optimum total dietary NDF level will vary depending on the quality and particle size of the forage(s) in the diet. When the structural or particle size of the forage in the diet is compromised, total NDF in the diet needs to increase (see table below). Either more high quality, fine particle size forage or a fibrous by-product will need to be included in the diet to increase NDF content. Because the NDF in by-product feeds and high quality forages is highly digestible, a high total dietary NDF concentration will have minimal impact on DM intake.
Forage NDF, percent of DM
Numerous studies have shown that as forage NDF in the diet increases, DM intake decreases. This relationship is very true when alfalfa or legumes are the major forage source in the diet, but isn't as true for corn silages or some of the newer high quality grass species now being grown. Research at Minnesota a few years ago found cows ate as much TMR with high quality orchardgrass hay (60 percent NDF) as with alfalfa hay (40 percent NDF) and the orchardgrass hay was slightly better at maintaining milk production when corn was substituted in diets for hay. Here is where NDF digestibility information on the forage can help determine the impact of NDF on DM intake. The range in 30 hour NDF digestibility (percent of NDF) within forage classes is quite high; corn silage - 50 to 65 percent, alfalfa - 35 to 55 percent and grasses - 30 to 70 percent. Being at the upper end of the NDF digestibility range will help promote DM intake, especially for corn silages and grasses. The challenge this year will be to harvest a large quantity of highly digestible forage to build forage inventories.
For most diets, forage NDF should be about 20 percent of the DM (18 percent to 22 percent). When feeding less than 20 percent forage NDF diets, total diet NDF should increase with inclusion of digestible fiber by-product feeds substituting for forage and corn in diets (see below for the relationship between total and forage NDF in diets).
Forages are the source of long fiber particles needed in the diet to promote rumination and a good rumen mat. Check forage and TMR particle length with a Penn State Particle Separator box. Guidelines for both forages and TMR are below.
Avoid excessively long forage particles (over about 3 inches) on the top screen as these are generally not consumed. Conversely, very short or fine particle size forages (less than 1 inch) can contribute to rumen acidosis. The time to check forage particle length is at harvest on the way into storage.
Low forage diets
Here are some recommendations for feeding low forage diets. Low forage generally means forages will be closer to 40 percent of the DM than 50 percent.
Include good, but not excellent quality forage in the diet. The forage content of the diet will decrease as NDF content of the forage increases. However, the forage quality also has to be good enough that cows will eat it. Select forages with a good NDF content and high NDF digestibility for maximizing milk production at lower feed intakes.
Have adequate, but not long forage particle size. Cows generally will not eat forages in a TMR with particle sizes of six inches or longer. Particle size both the TMR fed and refusal to see if cows are sorting. If the top screen particle measurement difference between the fed and refusal is over 10 percent, be suspicious of sorting.
Limit rapidly fermentable feeds in the diet. As forage content of the diet decreases, physically effective fiber content of the diet usually declines also. With less cud chewing and, consequently, rumen buffering from saliva, the risk of acidosis increases. Limit the inclusion of rapidly fermentable feeds like high moisture corn and finely ground corn in the diet. Substitute high digestible NDF by-product feeds like, soyhulls, beet pulp, corn gluten feed, whole cottonseed or cottonseed hulls for both forage and some of the rapidly digestible carbohydrate feeds in the diet. Below are guidelines for non-fiber carbohydrate (NFC) levels in the diet in relation to total NDF and forage NDF in the diet.
Forage NDF Total ration Ration NFC,
minimum NDF minimum maximum
---------------------------- percent DM basis -------------------------------
19 25 44
18 27 42
17 29 40
16 31 38
Include dietary buffers to replace saliva buffer. Adding a buffer to the diet will help reduce the risk of acidosis. Feed a minimum of six ounces/cow.
Feed bunk management. Don't overcrowd, forcing competition for bunk space and slug consumption of fermentable feeds. Feed for some weighback and keep feed (TMR) available to cows at all times by pushing up frequently or feeding more.[[In-content Ad]]
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