The author is a dairy specialist with Vita Plus.
The 2019 growing season was one of the most challenging seasons many of us have ever seen. Several areas had severe winterkill; spring planting delayed by cool, wet weather; and a short summer with more rain and a wet fall. In contrast, other areas experienced lower than average precipitation.
In short, our forage growing season and subsequent inventories were really messed up. Needing to get some kind of feed from their acres, many farms planted alternative forage species, and now have inventories of some “unfamiliar” feeds. These include small grain silages, cool-season grasses (such as ryegrass), sorghum-sudan grasses, forage peas, soybean silage, and whatever else that could be windrowed and chopped.
How do these unique forages fit into our dairy rations?
Cows are adaptable
Dairy cows were born to eat a variety of forages, and most of these “unfamiliar” forages have been fed to dairy cows for a long time. In fact, all the forages listed above were commonly fed to dairy cows prior to World War II. The Midwest’s top choices since the 1940s have been alfalfa and corn silage. While feeding more cereal grasses — such as triticale, rye, or oat silage — or soybean silage seems new to us, it certainly is nothing new to a dairy cow.
That said, feeding alternative forages comes with some nuances. While not intrinsically true in all rations, most of the time we see alternative forages replace legume silage in the diet because corn silage inventories on our dairies are relatively fixed, although this is not the case this year. Comparing alternative forages to alfalfa is a great starting point, but we must first recognize that our traditional quality metrics aren’t necessarily applicable to alternative forages.
As an industry, we are not well-versed in the details that make average alternative forages great forages. We are still learning how to evaluate, incorporate, and manage these alternative forages.
When strategically incorporated into the feeding plan, alternative forages can provide us the opportunity to fill in the gaps without leaving milk on the table. These forages are providing protein and fiber and both need to be accounted for.
Protein matters first
The very first consideration of any alternative forage in inventory is its protein content. In general, if the crude protein (CP) content of the alternative forage is greater than 14% to 15%, the forage should be a prime candidate for inclusion in the lactating diet to help reduce purchased protein cost.
Cereal forages, such as triticale or rye silages, harvested early (at the flag leaf or early boot stage of maturity) may contain 15% to 18% CP and 42% to 48% NDF. Likewise, early vegetative ryegrasses, soybean, and pea silages commonly contain 16% to 18% CP. Note the protein content of grass silages is largely dictated by soil nitrogen fertility status and harvest timing.
Now for the differences.
Grass forages are much lower in calcium and can be very high in potassium because grasses are luxury consumers of soil potassium. Therefore, dietary calcium and potassium levels need to be double-checked in the ration.
If the grass forage was grown on high-potassium soils, dietary magnesium needs to be monitored very closely using wet chemistry procedures at the laboratory. High potassium levels in grass forages can interfere with magnesium utilization by dairy cows. Thus, we often supplement a bit more magnesium in our diets when alternative grass forages are fed to lactating dairy cows.
Understand fiber type
A second difference in alternative forages is the type of fiber. As compared to alfalfa, cool-season grass forages will have less lignin and more hemicellulose. As a result, cool-season grass forages have less indigestible NDF and greater NDF digestion potential as compared to a typical alfalfa silage. That all sounds perfect, but it also delivers an unfortunate quirk.
Research has shown that legume forages, including alternative pea and soybean silages, have a greater passage rate as compared to cool-season grass forages. This means alternative legume forages have less rumen fill effect, and grass forages may cause more rumen fill even when diets are formulated at the same NDF concentration. This may result in slightly lower dry matter intakes (DMI) in high-producing cows consuming diets with more cool-season grass inclusion, even when diets are formulated on an equivalent NDF basis.
In contrast, this may not be true when feeding sorghum-sudan grasses to lactating dairy cows. Sorghum-sudan forages are C4 grasses and have fiber levels very similar to corn silage. Replacing corn silage fiber with sorghum-sudan grass fiber in properly balanced diets typically does not result in DMI differences.
Consider forage hygiene
Pay particularly close attention to the ash content in all your forages this year. High ash content can make some forages difficult to accurately test. It is also a risk to normal fermentation.
Soil contains a host of contaminates that can alter fermentation. Add this to the difficulty of getting forages dry enough this year, and you may have a recipe for a disaster. A wet forage with heavy soil contamination can lead to the production of butyric acid and other harmful biogenic amines.
If you harvested any forages after the temperature dropped, it may not progress through a normal fermentation. If possible, feed these forages while it is still cool as they can become very unstable at feedout during warmer weather. Evaluating your harvest techniques and properly applying a quality inoculant can help manage some of these risks.
What is your plan for the coming forage season? Now is an excellent time to have these conversations with your team. If winterkill on your alfalfa stands has you at wit’s end, one of these alternative forages could fit into your system. If you have fields where you perpetually deal with dry spells and corn silage is not yielding, you may consider more water efficient plants.
Plan to supply nutrients
Winterkilled alfalfa doesn’t provide any protein for your ration and late-planted corn may provide little to no starch in the silage. All the nutrients needed for the cows and their ration can be accounted for, we just need a plan for what we will have and what we will need to replace.
We must play a bit with diets containing more alternative forages to find a dietary NDF level that maintains DMI, rumen health, milk components, and milk yield. Despite nuances between feeding our cows traditional alfalfa and corn silage-based diets, we have observed excellent milk production and maintenance of milk components when alternative forages are included in their diets.
