Avoid Pasture Bloat

By: Heather Smith Thomas

Bloat is a common problem in ruminants, if they can’t get rid of extra gas produced by rumen microbes

during digestion. Putting hungry cattle on lush legume pastures, such as alfalfa—especially in pre-bloom stage—is most dangerous. It’s less dangerous once plants are mature, with lower protein level. Wheat pastures can also be a problem. Nearly any pasture that is high in protein content and low in structural fiber can be a risk under certain conditions.

Dr. Bill Pinchak, beef cattle nutritionist and Professor, Texas Agri-Life Research and Extension Center, says winter cereal small grain pastures can present challenges. Pasture bloat occurs in every state and throughout Canada.

Dr. Ron Gill, Texas A&M says that in areas where wheat is grown, bloat is common on highly fertilized pastures and immature stands. “We get bloat with a flush of growth, along with high nitrogen content, or a change in pH in the rumen that shuts things down a little. There are also issues with calcium imbalance. Producers don’t always pay attention to minerals; lack of calcium affects smooth muscle contractions and may hinder ability to push some of that gas out of the rumen,” he says.

“Some folks use a mineral mix containing high levels of magnesium–although yearlings on wheat pastures don’t have a problem with grass tetany. Cows grazing small grains are susceptible to tetany, and lack of consumption of mineral may be part of the bloat issue.”

Some legumes, like alfalfa, are notorious for bloat, but there are options today for types of legumes that are not as likely to cause bloat. “With wheat pastures, by contrast, I haven’t seen any varieties that are less bloat-prone,” says Gill.

Bloat is also related to weather patterns. Sometimes cattle don’t graze at regular times (waiting out a storm, perhaps) and then overload. “Another factor is related to days of rapid growth followed by cloudy days when nitrogen accumulates in the leaves but doesn’t have enough sunlight the next day to complete the photosynthesis process—to convert nitrogen into plant protein,” says Gill.

Tips to Minimize Bloat

“When grazing wheat pastures, producers are hesitant to put out something for bloat that does not also add performance,” says Pinchak. Products like Bloat Guard (poloxalene) are very effective if consistently consumed, but all they do is help prevent bloat,” he says.

With any bloat interventions, cattle must be trained to consume them before they overeat. “Stocker cattle generally come from different places, and their experiences with what they eat are different. To use a bloat product it takes time and investment to try to teach them what is safe to eat. This also applies to a mineral program, a different type of hay, or different pasture. If you plan to use a  n ionophore in a mineral, or a poloxalene block, the animals must be exposed to that and trained to eat it before they go on a bloat-prone pasture,” says Pinchak. The cattle must already be consuming it, because once they start to bloat they are not going to eat it.

“One thing to help reduce risk is to fill them up on a good high-fiber hay before they go out, so they won’t overeat. With wheat pasture, how much bloat we see is also related to the amount of pre-planting nitrogen fertilizer,” says Pinchak.

“We did studies looking at pre-planting fertilization rates, comparing 30, 60 and 90 pounds of nitrogen. We saw bloat at all levels, at least for a day or two, but with 90 pounds of fertilizer the risk for mortalities was high. I suggest using 40 to 50 pounds max if they plan to graze those pastures. If they pull the cattle off and later harvest that field for grain, they can top dress it with more nitrogen after the cattle are gone,” says Pinchak.

Some people provide long-stem hay free choice, such as big bales in the corner of a pasture. Cattle address their fiber needs by eating a little hay. Another tactic is to let the forage become more mature so it is not so lush, and graze it during the frost-free period. “Anything that upsets photosynthesis in the actively growing plant (such as frost) can cause bloat. In the coldest part of winter here, we don’t see bloat; it’s only when the plant is trying to actively grow and something upsets that growth pattern. In wheat, this is much more pronounced and predictable than with alfalfa or clover; you can have bloat any time during the growing season with those legumes, under certain conditions.” If it’s a pure stand of alfalfa, let it get taller and more mature. If possible, have alfalfa in a mix with grasses.

It helps to add roughage but also slows rate of gain. “Some producers in Texas plant Haygrazer (a sudan hybrid) or sorghum/sudan at the edge of the field or leave waterways grassed in so cattle have some dry matter in their diet,” says Gill. Cattle often eat a little roughage if it’s available to pick at every day. Haygrazer doesn’t slow gain because it has more energy than some forages and there’s not enough of it to change their intake much, and it does seem to help reduce bloat.

Another strategy is feeding a high-energy supplement. “You can increase gains and cut down bloat but it means feeding cattle while they are on pasture which isn’t practical in many situations. There are many self-fed mixtures. Some people add Rumensin and even though it’s not labeled for bloat it seems to help. Anything you can do to cut down massive death loss is worth looking at. Even if you reduce gain for a little while, that’s still better than losing a lot of animals,” says Gill.

Pinchak says the nice thing about using an ionophore is that you also get a positive response in performance. “It will improve average daily gain. If you simply use something like poloxalene and don’t have bloat, it’s just an extra cost,” he says.

Other Products

“We’ve worked with several products, including an enzyme-fortified product (BovaZyme) that has a lot of enzymes. It didn’t eliminate bloat but it was less severe. There are several options for bloat prevention, but the important thing is getting the product into the animal. If they aren’t used to eating mineral and won’t eat a mineral pack, some people use a molasses block mineral or low-moisture tub that contains the bloat product,” he says.

“Another product that has worked pretty well is a liquid mix that is very high in fat. If we add more fat to the diet, there will be less bloat. Most bloat is caused by formation of a stable foam, and fat/oil tends to break up that foam. This is why things like corn oil, mineral oil, etc. can be used for treating acute bloat. If you feed a supplement that’s high in fat, and cattle consume it, this can decrease risk,” says Pinchak.

“One thing that works really well to prevent bloat is condensed tannins, but we don’t have any products commercially available that contain these. Tannins occur in some forages, and we’ve done some work with condensed tannin extracts like those used in the leather tanning industry, and these were very effective.”

Genetic Component

Some animals seem more bloat-prone. “It would be interesting to see whether it’s the genetics in the rumen bacteria (of that animal) or the genetics of the cattle. Does genetics of the animal lead to a different gut population, or is the rumen population influenced by environmental or other factors? We don’t have answers to that, but there are certain lines of cattle that have more bloat,” says Gill.

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