When you go into a feed store, crude protein is still king. In the old days, it was a chalkboard with a grid for pricing of various feed products. Everything, from cattle cubes to show feed to chicken scratch, is described and priced using protein in the name. Though the chalkboards have mostly been replaced with more modern means of communication, using protein as a primary description of a feed is still going strong to this very day.
The other place that protein is important is in the hay and forage business.
“I have some round bales of 12% protein grass hay for sale” might be a common thing to hear at a rural coffee shop. Or in alfalfa country, you could hear a hay farmer bragging about a second cutting of nice hay that tested “nearly 24% protein.”
In the dairy world, we have been able to move past using just crude protein (CP) as a forage quality description by adding relative feed value (RFV) to the conversation. Wait, what year are we in? Yes, here in 2022, we have struggled to move past the RFV approach that was “new” in the previous century! But still, in the areas I visit farms, and for alfalfa in particular, RFV is still used and along with CP is the common identifier of hay quality. We can do better!
RFV may be better, but . . .
I think the reason RFV took the place of CP in describing hay is that most people intuitively assume that RFV is a more broad-based description and surely includes protein in the formula. That, however, is not the case.
RFV only considers the acid detergent fiber (ADF) and neutral detergent fiber (NDF) of a forage. The lower the fiber, the less mature the hay was at harvest and the more nutrients it will supply to a ration. Thus, the higher RFV. All of this is mostly true, and in many or even most cases, higher RFV hay also has higher protein levels.
Doing a quick Google search to try and see how long ago RFV was introduced to the livestock feeding world had me stopped at an extension publication from 2004 suggesting a change from the old-school RFV to a new and improved concept of relative forage quality (RFQ). So, way back in 2004, North Dakota State University Extension Service was trying to convince feeders that RFQ was better than RFV and offered some supporting information to make the case. Some 18 years later, we still talk about RFV. It is a bit like VHS and Betamax video cassette recorders back in the day except, in this situation, Betamax was the technology that didn’t have the staying power. RFQ was a nice improvement as it does include both protein and fiber digestibility in the formula. But it has never seemed to catch on, especially in the West.
In the many intervening years, we have had other measures of forage quality like milk per ton or milk per acre that paired yield data with quality to help pick hybrid and allocate acerage. These are good and the science behind them is sound. Why, though, do we still keep going back to RFV?
The “Big Four”
In my view, there are four key items that determine feeding value when reviewing a forage analysis report:
• The first one to get out of the way is moisture content. Being sure you are not buying water at forage prices is the first step.
• Next, we will stay with the old-school guys and look at protein. More is always better unless there is nitrate in the forage or the forage has heated and the protein is bound.
• Third, and most importantly, pick a digestibility number. There are several of these that can work and asking the lab you use which they prefer as their “best” measure might be the way to go. Examples of these might be neutral detergent fiber digestibility in 30 hours (NDFD30), which tells the digestibility of the NDF fraction in 30 hours. Other labs may have an in vitro digestibility measure that attempts to best describe how much of the forage will be digested by the animal.
• The fourth and final is ash content. Buying dirt at forage prices is as bad as buying water or perhaps worse if it is in silage where it can lead to poor fermentation and animal health risks.
There is another problem as well with high-ash forages. High-ash forages are a real problem for the near infrared (NIR) process. High ash content not only reduces the quality of the feed, but it also reduces the accuracy of the lab analysis altogether. Using wet chemistry instead of NIR on high-ash forages is advisable. I would suggest asking your forage lab how to best handle high-ash forages to be sure they are analyzed and fed correctly.
I should also add that these four items to help replace RFV as a forage quality indicator are limited to things like picking and choosing what to buy or what to feed in various situations. When your nutritionist enters a forage analysis into the ration model, there are many more than four items of interest. This is where the exact analysis of a forage will be melded into a balanced ration, taking into account many nutritional and physical factors. For a quick look when pricing, buying, or selecting a hay, if RFV is all you have, that is better than nothing. Looking further to RFQ or milk per ton will encompass the four items suggested above with the exception of moisture content. The presence of potential toxins in forages is another topic that deserves attention.
What about corn silage?
And don’t forget that looking at corn silage analysis compared to alfalfa, grass, or small grain forages is like apples and oranges. Corn silage nutrient values are dominated by the starch (grain) content of the crop. Taking care to evaluate the fodder in corn silage alongside the starch content is the best way to be sure that you remember that corn silage is like two feeds in one. Assuming that the fiber is good just because the starch is high is a common mistake. High starch can result in low fiber values but that doesn’t mean the fiber is highly digestible. Keep in mind that the forage analysis process is a long way from being a perfect science. Handling the hay, smelling the silage, and ultimately seeing what the cows think about it is always best!