Things You Never Knew A Forage Test Could Tell You

Forage testing is the scorecard of a hay program and is necessary to meet feeding goals for livestock. However surveys show that most do not test hay. In the defense of farmers, good hay weather has been so infrequent that people really don’t want to see the results. You can almost hear them say, ‘I already know my hay is bad – why should I pay somebody to tell me something I already know!’ I sympathize.

Forage tests measure forage quality, but I will bet there are some things that you did not know it can tell you. So consider these even more reasons to test hay. What follows are some of the interesting things that you may not know a forage test will tell you.

First of all, the most important number is not the crude protein (CP) number. Protein requirements for most classes of cattle are pretty easily met by forages, especially mature cattle. Seldom do we need to supplement just for protein. Fiber values tell the story on forage quality. Yet we do not have an intuitive understanding of fiber as we do with CP. So let’s look a little closer at the fiber values on a hay test.

Acid detergent fiber (ADF) and neutral detergent fiber (NDF) are the most important and least understood parts of the report. The names themselves do not help understanding because they refer to the lab processes not to animal performance. These values are the most important because they are used to predict energy (from ADF) and intake (from NDF). And energy and intake are where forages limit animal performance.

Fiber values help to indicate legume content. These two values on a hay test are named for the proportion of forage left after boiling in either neutral or acidified detergent solutions. NDF is the total fiber in the forage (NDF) and ADF the total fiber minus hemicellulose. Since legumes have less hemicellulose than grasses, the NDF-ADF difference will be less for legumes that grasses. An NDF-ADF difference of 10 would indicate almost pure legume, while NDF-ADF differences for grasses will be 20 or higher.

High NDF values are a red flag. How much a cow will consume can predicted from NDF. An NDF of 40% (excellent legume hay) will have an estimated intake of 3% of body weight per day. An NDF of 60% (a typical grass hay) allows intake of 2% body weight. Ultimately, feeding a cow comes down to intake – how much she can eat per day. High NDF forages take a long time to pass out of the rumen.

Calcium-phosphorus ratio can also reveal legume content. Legumes grown in our region will have a Ca:P ratio of 2:1 or even higher, while our cool season grasses will be more like 1:1. So a wide Ca:P ratio means more legume. This little known fact really came in handy when a horse farm client wanted to know if a lot of hay they had purchased was in fact going to be a 50:50 mix of alfalfa and grass as they wanted. The forage test showed a very wide Ca:P ratio (>3:1). I predicted the hay was going to be mostly alfalfa. And it was.

Digestibility Terms. Total digestible nutrients (TDN) is the most frequently used energy term for beef cattle, and it is nearly always calculated solely from ADF. Labs differ in the equations used to predict TDN, sometimes markedly, so it is more important to compare ADF values if you are comparing hay quality values between labs. Getting your forage tested needs to be on your list of must-do’s this fall (after it warms up a little). This information will help you feed more efficiently, and it may even tell you some things you did not think possible.

Happy foraging. ~ Dr. Jimmy Henning, from Farmers Pride

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