Whether in a college dorm or hotel room, most everyone has had the experience of trying to cram clothes into a limited amount of drawer space. Cram and cram again — at some point, you just can’t cram any more.  

A similar analogy can be made to the amount of feed that goes into a cow. According to Kurt Ruppel, dairy management specialist at Cargill Animal Nutrition, there is a limit to how much fiber material — specifically, the cell wall material in forage known as neutral detergent fiber — can fit into a cow’s rumen at any one time. The limit, in fact, is 11 to 14 pounds. Once the limit is reached, the cow has “pressure sensors” in the rumen wall that tell her to stop eating. 

If you can only get so much fiber into a cow at one time, it’s important to use a highly digestible forage base so it will move through the system relatively quick, freeing up more rumen capacity, and supplying the cow with energy and nutrients.                

You can't get a good handle on the digestibility of your forage unless you "benchmark" them periodically with lab analyisis. With that information in hand, you and your nutritionist can do a much better job of formulating rations.

Focus on quality            

It’s really quite basic: Forage quality drives intake, and intake drives milk production, points out Limin Kung, forage quality expert from the University of Delaware.

For years, experts looked at neutral detergent fiber (NDF) levels as the main determinant of forage quality. While NDF is still very important, experts now realize there is more — much more.

You can have two forages that look exactly alike in terms of crude protein and NDF, but they can vary greatly in terms of NDF digestibility.  

Among 377 high-group total-mixed rations analyzed by the University of Wisconsin’s Marshfield Soil and Forage Analysis Laboratory, the average NDF digestibility was 57.2 percent, which isn’t all that surprising. Nutritionists aim for a NDF digestibility of about 60 percent in TMRs. What is surprising, however, is the range in NDF digestibilities among the 377 TMRs tested. That range, shown in the chart above, extends from 41 percent all the way to 74 percent.  

This is a significant issue, points out Pat Hoffman, dairy scientist and outreach program manager at the Marshfield research facility and testing lab. NDF digestibility can have a huge effect on dry matter intake and milk production potential, he says.  

You don’t need to convince Chris Hallada of the need for forage benchmarking. Hallada, nutritionist and forage specialist with the Vita Plus Corp., uses benchmarking to achieve greater consistency among forages at the 1,500-cow Emerald Dairy farm in Baldwin, Wis.

Improve ration consistency

“What we have been attempting to do is characterize the corn silage from one year to the next to try to minimize the ‘fall slump’ that we see” when switching to new-crop corn silage, she says. In the past, that drop has been as much as 10 pounds per cow per day.

This past winter, Hallada used benchmarking to solve a related problem. First-calf heifers were doing a good job of milking, averaging more than 80 pounds per day. But, the older cows fell short of potential. As Hallada puts it, the older cows were “just kind of poking along.” That prompted lots of questions, and eventually the problem was traced back to the late-season drought that affected areas of the Upper Midwest.

Thanks to the information she gained from lab tests of forage and TMR samples, Hallada made adjustments in the ration — specifically, the inclusion of more premium hay and high-fiber byproducts — to move the cows closer to their production potential.  

Make smarter decisions

In the case of low NDF digestibility, it may be necessary to supplement the ration with high-fiber byproducts like soy hulls, beet pulp or corn gluten feed, says Randy Shaver, dairy nutritionist at the University of Wisconsin. If the forage has high NDF digestibility, make sure that the cows are receiving enough physically effective fiber to stimulate cud chewing and rumination.

Forage with high NDF digestibility allows you to increase the forage-to-grain ratio of your ration, because the forage can meet a higher percentage of the cows’ energy requirement. That, in turn, results in a less-expensive ration than one relying heavily on grain. And, it promotes better rumen function and overall cow health. 

If you really want to fine-tune the process, consider adding extra bunker silos or piles, so you can group forages by quality. If forage coming out of one pile is significantly higher in NDF digestibility than the other piles, earmark that forage for high-group cows.

Having more silos can allow you to blend your forages into the rations according to quality, thus minimizing some of the production “hiccups” that occur as cows make a transition to new-crop silage, says the University of Delaware’s Kung.

After all, cows crave consistency. And, better consistency is what you gain by benchmarking your forages — and knowing ahead of time what ration adjustments you need to make.

Pick the right lab

When doing forage benchmarking, choose a lab that has a good handle on NDF digestibility testing.

At least four commercial testing labs do the type of wet chemistry that will provide meaningful results. Those labs are:

  • University of Wisconsin Marshfield Soil and Forage Analysis Laboratory, Marshfield, Wis., (715) 387-2523.
  • Dairy One Milk Laboratories, Ithaca, N.Y., (800) 496-3344 or (607) 257-1272.
  • Cumberland Valley Analytical Services, Maugansville, Md., (800) 282-7522.
  • Dairyland Laboratories, Arcadia, Wis., (608) 323-2123.

Don’t get bogged down with the nuances of 30-hour NDF digestibility tests versus 48-hour tests. Pick one parameter and ask for it each time — from the same lab. That way, you will compare forages from season to season, cutting to cutting, on a consistent basis.