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The function of forage in the ration

Progressive Forage Intern Sundee Holtman Published on 09 July 2021

Function. A word with seven definitions, one being “a group of related actions contributing to a larger action.” Forage. A word with four key functions.

According to Dr. Jeff Lehmkuhler, an extension professor for the University of Kentucky’s Department of Animal and Food Sciences, these four forage functions are important to consider when implementing a ration around forages for various ruminant livestock species.

Forage functions

Forages provide a main source of energy. The fermentable carbohydrates available in forages can provide upward of 60% to 80% of the energy livestock utilize.

Further, forages provide protein that is valuable when it comes to the rumen and its microflora. These proteins deliver the basic peptides and ammonia gut bacteria is going to use to build their own amino acids. As those bacteria get washed out of the rumen and digested farther down the animal’s digestive tract, microbial proteins provide the basic building blocks for the amino acids the animals are going to use for milk protein and muscle synthesis.

Forage also provides fiber that is very important in maintaining rumen health, gastrointestinal tract health, reducing the risk of digestive upsets, and they help the ruminant maintain the proper pH in the rumen by stimulating rumination.

The last key function is to provide nutrients. Many forages can actually provide nearly all, if not all, minerals and trace minerals, especially when producers incorporate alfalfa and other legumes. In addition, a significant number of vitamins are delivered to ruminant animals through forages. This group of functions contribute to the larger action, forage ration efficiency.

Developing an efficient feeding program

“It really is a balancing act,” states Lehmkuhler. “On one side we have the supply of nutrients coming in, and on the other side we have the animal’s requirements.”

Starting with nutrient supply, producers must evaluate the concentration of nutrients in their forages. A good place to start would be to send your forage samples to a lab. Here they’ll analyze your sample to look at mineral content, fiber content, protein content and more.

The next part of nutrient supply is digestibility. As forages mature, their cell wall lignifies and begins to make up more of the plant. This lowers digestibility and reduces the feed intake of the animal because it takes a longer time for that rumen microflora to reduce the forage particle size to the point it can pass out of the rumen and allow that animal to consume more. In reflection, the supply side is really a two-function component.

As for animal requirements, they will obviously differ depending on the type of animal you are dealing with. Age, genetics, purpose and current reproductive status are all attributes to include in your equation.

Other major considerations

Good rations start with good samples, but if you were to go out and try to sample your pasture, the question becomes “Did my forage sample represent what the animal actually grazed?”

Livestock are selective to what they consume in pasture. This means we must factor in the fact that what we send into the lab may not be representative of what the animal consumes. Plus, forages change and mature in pasture. So how do we mitigate making incorrect intake predictions? First, keeping your pasture in a vegetative state is important, which means that in some situations you may need to harvest or clip those pastures to reset them back to the vegetative growth stage.

You can also use a single component from a forage test to help you more accurately predict pasture intake, says Lehmkuhler.

“We can get this estimate of intake by using the constants, 120, divided by the neutral detergent fiber also known as the NDF, a value found on a forage test,” says Lehmkuhler. “If we look at dry matter intake [DMI] expressed as a percent of bodyweight, it would be equal to that constant of 120. In this example, I’m assuming that my forage test came back at 62 percent NDF, and that would be on a dry matter basis. 120 divided by 62 is 1.9 percent. Now we can take 1.9 percent and multiply it by our animal size; in this example, I’m using a 1,300-pound cow. Multiply 1,300 by 1.9 and divide by 100 to convert that percentage to its decimal form, and we come up with a value of 25 pounds of dry matter.”

Anti-nutritional factors should be another consideration. This could include alkaloids, mycotoxins that can reduce rumen contractions and essentially shut down feed intake, and nutrient deficiencies. Other issues may be more obvious, like heat stress, mud and other environmental factors.

Lehmkuhler also notes that one component which gets overlooked if we’re purchasing hay is taking a little time to do a real inspection of it. This alone can tell you when that forage was harvested and the conditions it was harvested in. So pull some hay out of the middle of the bale, look at how mature it is, look at the leaf-to-stem ratio, look for seedheads, look to see if the flower component is still on it versus if the seeds are falling off, which will give you an idea of whether the forage was rained on and sat in the sun, and look at the color and smell. Each of these items gives clues to how this forage will impact livestock intake.

Though numbers and equations help us to become more efficient, we should understand that when creating a ration based around forages, or any ration, monitoring body condition will give us ultimate hints that can lead us to knowing whether we are on target or not.

Last, to ensure the nutritional requirements of our livestock are being met, we may need supplements. In many situations, there will be deficiencies that need to be corrected. In other situations, we may want to stretch our forages and increase the carrying capacity of our land. Further, our livestock genetics are just not the same as they were 30 years ago. Milking levels are higher, weight is higher, in some breeds muscling is heavier, etc. Therefore maintenance is higher.  end mark

Sundee Holtman is a 2021 Progressive Forage intern.

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