Recently, there has been a lot of interest in using cover crops as a forage source. Research in the Northern Great Plains and Intermountain West regions have found favorable evidence on the utility of cover crops as a grazing source. With so many options to choose from, where does one even start?
One of the advantages of having many options of cover crop species is the flexibility it provides producers in planting and harvest. Cool season annual grasses, like wheat, barley, and oats, can be planted in the spring to provide high-yielding, high-quality forage throughout the summer. Additionally, as a recent study in Montana has found, they can also be planted later in the summer, and still produce a great quality forage for fall grazing. Warm season grasses, like sorghum, sudangrass, sorghum x sudangrass hybrids, and millet, have to be planted later in the summer, once soil temperatures in the top 1” have reached approximately 60°F, but provide great summer and fall grazing as well.
Brassicas, which include canola, turnip, kale, and mustard, are well-adapted to many areas of Montana. They have rapid fall growth, making them ideally suited as a fall grazing option. They also have the ability to retain their forage quality fairly late into maturity, providing a good-quality forage even when grazed at a more mature stage. Care must be taken to plant these species after June 15, as they can bolt if planted too early, decreasing both aboveground and belowground growth.
Pulses, or annual legumes, are a very high-quality forage source, and include species such as peas, lentils, chickpeas, and fababeans. Studies in North Dakota have found that peas had similar, if not better quality than alfalfa, and can provide a great grazing source for livestock.
Comparing Forage Quality
When comparing forage options, many use cereal forages and pulses as their “go to species” for grazing. Breeding programs have been in place for many years to improve forage digestibility and nutrient levels in species such as wheat and barley. ‘Willow Creek’ winter wheat has been a popular forage option since its release in 2005. It produces relatively high yields when compared to its counterparts bred for grain production, with crude protein (CP) levels in the mid-teens through early heading, and lower nitrate levels compared to similar grain cereal varieties. Several forage barley cultivars have been in use for many years, with some of the popular varieties being ‘Lavina,’ ‘Haybet,’ and ‘Hays,’ among many others, and new ones still being developed. They have similar forage quality to ‘Willow Creek,’ with a recent study in Bozeman showing CP levels between 16 and 21% and total digestible nutrients (TDN; an indication of energy availability) between 60 and 65% at early heading.
Pulses are a great source of both protein and energy, and often far exceed the protein levels of cereal forages. In a 2011 study at NDSU, peas were found to contain 87% TDN and 25.5% CP. In the same study, barley had 85% TDN, but only 13% CP. When peas were grown in a mixture with cereal forages, we often see improved yields, along with improved nutrient levels compared to cereal forages grown alone. And when grown in a mixture, the nitrate risk of the cereal forages is typically reduced, adding another bonus for livestock producers. The biggest problem many have when growing them together is the drying process, as it takes peas much longer to dry down compared to a cereal forage.
What are some concerns with cover crops?
Depending on species, there are some risks to consider. One of the biggest issues we see in Montana is nitrate toxicity. Oats are typically associated as the species with the highest nitrate potential, but wheat, barley, warm-season grasses, and even brassicas all have potential to accumulate nitrates as well. In a grazing study conducted in 2016 in Bozeman, MT, two oat cultivars and thirteen forage barley cultivars were evaluated for forage quality and palatability. After evaluating the forage quality, it was found that the oat varieties were on average between 2.1-2.53% nitrate, while the forage barley varieties were between 0.46-.23%. Typically, anything over .5% is not recommended to be fed to pregnant animals, and anything over 1% should not be fed to any animal unless diluted. This illustrates how “hot” oats can potentially be, with the barley varieties often being “safer” but still having potential to cause issues. Other things such as fertilization, environment, and harvest management can also have major impacts on nitrate risk. For more information on nitrates, please refer to the Extension publication Nitrate Toxicity of Montana Forages (MT200205AG), or the Fall 2014 issue of Big Sky Small Acres for the article “Nitrate Toxicity in Hay and Pasture Forage."
Another issue of concern is prussic acid, which is basically cyanide poisoning. This is typically only seen as a risk in warm-season grasses, and has similar risk of occurrence as nitrates. Typically, whenever the plant becomes stressed, the risk of toxicity is increased. Sorghum is usually at the highest risk, followed by sorghum x sudangrass, then sudangrass. A recent study at the University of Idaho also found millet to have high levels of prussic acid, contrary to previous literature. In order to decrease the likelihood of livestock toxicity, don’t graze plants that are less than 18-24” in height, or any plants that have been severely stressed. Haying and ensiling will help to decrease levels, as the chemical is volatile, and once the plant has been cut, the chemical will start to be released.
Other issues in Montana have been seen in buckwheat and some species of clover. These forages have potential to cause photosensitivity issues, with affected animals exhibiting discoloration of the skin which looks like severe sunburn, and even loss of hair. For this reason, it is generally not recommended to use buckwheat in a mixture where animals are expected to graze.
There are many options to choose from when deciding what to plant for a fall grazing source. It is best to match species to environment and the needs of the livestock when making planting decisions. For more information, or if you have any questions, contact Dr. Glunk at emily.glunk@montana.edu or 406-994-5688.