Prevent Bloat on Fall Pastures
Risk of bloat can increase after the onset of frost.
Bloat can be a frustrating problem for producers, and fall pastures may hold greater risk under certain conditions. Emily Glunk, Extension forage specialist at Montana State University, says the higher the percentage of certain legumes in a pasture, the higher the risk of bloat.
“Fall weather can further increase likelihood of bloat after a frost,” Glunk says. “Ice crystals puncture cell walls within the leaves, causing soluble proteins to leak out and become more available more quickly within the rumen. Those soluble proteins lead to buildup of foam in the rumen that eventually causes bloat.”
Other plant parts, like microbial slime and plant cell membranes, can also combine with the soluble proteins to form stable foam. The foam then rises above the top of the rumen contents and obstructs the valve between rumen and esophagus, hindering the cow’s ability to belch.
“If a producer is trying to graze alfalfa in the fall, or cereal grains like winter wheat, I recommend pulling cattle off that pasture after a light frost, and waiting a couple days or so before putting them back in,” she explains. “This allows time for the plants to decrease those soluble proteins. If it was a killing frost, after which the plants go dormant, wait at least five to seven days.” By that time the plant has gone dormant, dried out and is more like hay — and not as risky.
Wheat pastures can cause bloat after a frost.
“Usually bloating occurs on the cereal grains that are bred to have higher-quality protein, so there is higher protein availability to start with,” Glunk explains. Legumes tend to have high-quality protein compared to grasses.
Many producers don’t realize that alfalfa isn’t safe for grazing until several days after a killing frost.
“There are various recommendations,” she says. “Some people say you only need to wait three days, and others say five to seven. I like to play it safe and wait long enough to decrease [the] likelihood of problems.”
Other options to consider are preventatives like bloat blocks or lick tanks that contain poloxalene. Glunk says poloxalene can help prevent foam formation by lowering the surface tension of frothy foam and decreasing the foam’s ability to contain gas. The esophagus is not blocked and the animal can expel gas normally.
“The gas itself is not as much of a problem as the froth,” she explains. “Gas is produced by normal digestion via fermentation. Cattle are constantly producing gas. As long as they can get rid of gas and this process is not obstructed, they do fine.”
Another strategy is to let a legume mature before grazing. This allows for more dilution of soluble proteins due to an increase in the fiber component of those forages, which decreases digestibility, according to Glunk. An alfalfa pasture at 100% bloom has less likelihood of causing bloat than a pasture where only 10%-15% of the plants are blooming, as plants at a greater level of maturity are less lush.
Some producers mow a legume pasture, allowing the plants to dry a bit, then use electric fence to allow access to small strips at a time.
“When you swath and let it dry, it’s similar to hay,” Glunk says. “The benefits to swath grazing versus stockpiling is that you can cut forage at the stage of maturity you want it, and the plants won’t become overly mature with nothing but stems. As long as it’s been cut and on the ground, dried out (you’ve waited the seven or more days before grazing it) it will be similar to hay, and safer to graze.”
Editor’s Note: Heather Smith Thomas is a freelance writer and cattlewoman from Salmon, Idaho.