Alfalfa, the queen of forages, has long been associated with lactating dairy cows. This warm season forage has provided valuable fiber for the rumen while complementing total mixed rations (TMR) with readily available crude protein. However, this fickle queen can spell trouble for dairy farmers who manage their hayfield for optimum quality. One doesn’t have to look far to find a dairyman frustrated by weevils, fertilization schedules, or weather patterns that complicate this valuable crop.

Frankly, some years are better than others regarding getting even half the cuttings put up right. When the harvest window is challenged, this plant is known to lay down extra fiber, which slows the herd’s intake. However, sometimes you just have to feed what you’ve got. Understanding how the fiber will perform in the rumen will help ensure the ration fed will maximize digestion and, therefore, production.

Fiber analysis has improved

Neutral detergent fiber (NDF) comes from multiple sources in the ration. Undegradable NDF (uNDF) tells nutritionists how much of the fiber is not degradable and, therefore, how much energy can be obtained from that fiber. Taking that one step further, potentially digestible fiber (pdNDF) describes how much of the fiber is potentially degradable. This metric is calculated by subtracting the uNDF value from 100.

“Potentially” implies that the amount of fiber that is degradable depends. If the feed incubated for a long time, it will degrade. If it is taken out too early, there will be little to no degradation of the fiber. If the feed passes through the rumen too fast, poor digestion results.

A Virginia Tech team tested alfalfa versus orchardgrass in mid-lactation Holsteins to better understand the importance of how the different fibers impact the flow rate through the rumen. “We formulated the ration to hold NDF equal at 30% of the ration,” described Gonzalo Ferreira, associate professor of ruminant nutrition at Virgina Tech on the September edition of the “Dairy Science Digest” podcast. “Ten percent came from corn silage, 10% was from hay, and 10% was from from concentrate,” he explained. Their findings were recently published in the Journal of Dairy Science.

Ultimately, NDF supports milkfat production through a multistep improvement of rumen health and fermentation. Chewing is encouraged, with improved saliva production buffering the rumen with the ideal pH that results in an improved environment for the rumen microbes to digest more NDF, unlocking energy and protein for milk production.

Faster flow

Generally, when you compare the legume alfalfa and the temperate orchardgrass, you’d expect an apples and oranges scenario. The kinetics of the rumen is manipulated by what goes into the cow.

Looking at the uNDF of this chart, one would likely select orchardgrass over alfalfa for improved intakes. But it doesn’t tell the whole story. Alfalfa is very efficient in degrading fiber in the rumen. Even though alfalfa has higher uNDF, the pdNDF is digested quickly. Within 48 hours, the pdNDF of Alfalfa is 98% digested, whereas that’s only 78% in grass. Also, this faster passage rate of alfalfa allowed the cows to consume more feed.

For all milk parameters such as volume and components, the Virginia-grown orchardgrass performed as well as the Kansas alfalfa in the experiment.

“The delicate balance between the rates of degradation and passage determines the effective utilization of fiber,” described Haley Galyon, a graduate student at Virgina Tech who was involved with the project. For the feed to be digested, it has to be exposed to the degradation. So, if it passes too fast, it won’t have time to be fully degraded.

It’s all about the formulation

Producers are likely right at the cusp of harvest with their eyes on cold temperatures moving in. This sweet spot is the perfect time to collect samples of the forages from the recent growing season.

Ordering kinetic tests from the lab will characterize the 24-, 30-, 48- and 240-hour rates of fiber digestion, allowing your nutritionist to better predict how the hay will impact intake. While these in vitro digestibility tests are expensive, so is compromising rumen efficiency. Don’t leave milk on the table just for a few dollars on a forage test.

Alfalfa remains queen for the ability to provide digestible protein and rapidly degraded pdNDF. If you’re frustrated with your patch of alfalfa, be sure to sharpen your pencil to calculate cost of production before transitioning it over to an annual. There’s not a one-size-fits-all recommendation for forage; every dairy has a unique forage platform that works for their operation. In the end, high-quality homegrown forages more often pencil a positive return than purchased feed. Return on investment must be part of the forage platform discussion.

To learn more about this topic, listen in to the monthly podcast, “Dairy Science Digest” on your favorite podcast platform. The research findings were summarized in a peer-reviewed open access Journal of Dairy Science at article found at www.journalofdairyscience.org.