This past summer, a grazing research trial at the University of Guelph's New Liskeard Agricultural Research Station examined the effects of supplementation on pastured animals' growth performance, carcass traits, fatty acid profile and palatability traits. While research trials happen here year round, this trial was special in that the 39 Angus and Angus cross steers were grazing 80% alfalfa, and didn't have one case of bloat! How was this possible? Well, like any good producer knows, an ounce of prevention is worth a pound of cure. To know how to prevent bloat we first must know how it works and when bloat is most likely to occur.
How Bloat Works
There are two forms of bloat; free gas and frothy. Free gas bloat is caused when there is a build-up of gas in the rumen because the animal is unable to eructate (burp). This can be caused by several things, including an obstruction in the esophagus or pressure on the vagal nerve. The second type of bloat is frothy bloat. Frothy bloat is more common and occurs in feedlot cattle and cattle grazing lush pasture.
The cause of frothy bloat is complex and not 100% understood yet. What we do know is that frothy bloat is a build-up of gas bubbles that become trapped in the rumen in a stable foam made from soluble proteins. It has often been thought that soluble protein level in the plant is the main cause for frothy bloat; however research has shown that soluble protein, while a contributing factor, is not the sole cause of frothy bloat as researchers were not able to correlate the amount of protein in ruminal fluid to incidences of bloat. It has been suggested that chloroplasts that have been broken by chewing also play a part in the production of foam, as researchers were able to correlate the amount of chlorophyll in rumen fluid to the incidences of bloat(i).
Legumes are generally considered bloat-inducing plants, but young cereals and even lush grass can also cause frothy bloat. However, some legumes such as birdsfoot trefoil are considered bloat safe because they contain condensed tannins. Condensed tannins are considered to be anti-nutritional as they interact with proteins in feed, saliva and microbial cells which alters the digestive process and keeps the soluble protein in the plant from interacting to the same degree in the rumen, therefore preventing bloat (ii).
This article will focus on bloat with alfalfa. Alfalfa is easily broken down in the digestive tract, leading to a high passage rate through the animal. While a high passage rate is good for getting more feed into the animal, it is not good in terms of bloating risk. Plants that have a fast rate of break-down lead to bloat because the microbes in the rumen can rapidly break down the cell walls of the plant, releasing the soluble proteins and chloroplasts faster. Alfalfa varieties that have a slower digestion rate are being developed to lower the bloating risk in cattle, however early research into these varieties has shown mixed results in their ability to reduce rates of bloating (iii). It is important to keep in mind that these "bloat safe" varieties of alfalfa are still being developed and improved, as we are in the early stages of breeding and development.
Grazing alfalfa in spring usually has producers extremely worried about bloat -- this is because the vegetative stage of the young alfalfa plant is especially bloat provocative. Alfalfa that is in an early vegetative state, such as pre-bloom or early bloom, is considered to be the most dangerous for inducing bloat but as the plant matures the incidence of bloat decreases. Young plants are the easiest to digest as the stalks have not yet developed much lignin (lignin is the reason that plants become "stemmy"). Lack of lignin makes the whole plant, rather than just the leaves, easily digestible.
You may have heard that once a killing frost has hit alfalfa it is safe to turn cattle out into it. This is a myth. One killing frost will cause plant cells in the alfalfa to rupture while the plant is still intact, which actually increases the bloating risk. To be safe to graze after a killing frost, there must be at least a week of -9°C temperatures for the alfalfa to dry down before the risk of bloat is reduced (iv). Remember that if the plant is still green there is a bloat risk!
How producers manage their animals on alfalfa and other bloat-inducing forages is also important. When first introducing animals to alfalfa, make sure the animals are full of other slower digested feeds such as grass hay. This will limit the amount of fresh pasture they can gorge on and help reduce the immediate bloat risk. Once animals are on alfalfa it is also important to keep them on it rather than removing them and re-introducing it. This is easier on their digestive systems as the rumen microbes adapt to the diet the animals are consuming. The amount of precipitation alfalfa receives is also important to consider. Moving cattle in the rain is far less dangerous than 1-3 days after a rain when plants will be rapidly growing(iv). The same goes for when weather turns from mild to warm. The increase in temperature will kick start the plant's growth mechanisms causing it to grow rapidly which results in lush plants. If you are using alfalfa in a rotational pasture setting, it is advisable to move the animals after the morning dew has burned off. This is because soluble protein levels may change during the day, with the highest levels occurring in the morning (v). By moving the animals to a fresh pasture in the afternoon, the levels of soluble protein are going to be at the lowest level for a plant of that growth stage.
Pharmaceutical Bloat Preventatives
Even when practising good grazing management on alfalfa, it is still a good idea to use a pharmaceutical method of bloat prevention. This is an added cost, but losing animals to bloat is also costly to a producer. There are two main pharmaceutical methods on the market to control bloat and they come in a variety of delivery methods. A common feed additive for controlling bloat is monensin. Monensin works by changing the microbial populations in the rumen and can reduce the incidence of alfalfa bloat by up to 80% (iv). Elanco markets monensin as Rumensin" and sells it in the form of a bolus (Fig. 2). Rumensin in bolus form is convenient, as once it is inserted into the rumen producers have coverage against bloat, but there are a few factors that need to be considered before opting for this route, including the type of animal. For example, you wouldn't want to use rumensin boluses on cows year after year as the plastic casing which houses the monensin stays in the rumen and doesn't break down.
However, boluses are a good choice for backgrounding or finishing animals as the number of times they have to be retreated is minimal. Another thing to be aware of when using a Rumensin bolus is that you can't see when it is running out of active ingredient. There have been cases of the bolus running out before it should. This did lead to the manufacturer reducing the stated time the bolus is active for, but it is still a good thing to keep in the back of your mind. Monensin can also be added by feed mills into pellets, so if you are supplementing on pasture it is possible to feed monensin daily. A down-side to feeding your bloat control is that some animals may get pushed out of the grain before consuming their needed amount of drug, or in some cases animals may choose not to eat grain at all.
The other compound used for bloat control is poloxalene, which acts as a surfactant in the rumen. Surfactants lessen the surface tension in liquid, so when used in bloating cattle, it lessens the surface tension of the foam allowing the foam to fall back into a liquid and releasing the gas, enabling the animal to expel it (vi).
Phibro Animal Health has a top dress poloxalene product available in Canada which is marketed as Bloat Guard". Producers simply top dress grain or mix it into a loose mineral supplement. An advantage to using this method is that it is easy to use, but like feeding Rumensin some animals may not consume enough of it to be effective. When it is consumed in the correct minimum dosage, the risk for bloat is lower using poloxalene than Rumensin. In addition, Rafter 8 sells a liquid poloxalene called Alfasure". This product is measured into the water source using a dose-a-tron. An advantage for this is since every animal has to drink, you can be sure that they are all getting a minimum dosage of poloxalene. The disadvantage is that it takes a little more work. Producers have to make sure that the cattle have no other access to water in any form, and water lines and troughs need to be checked for leaks and overflows to avoid using up the Alfasure. Using Alfasure also allows the producer to adjust the amount of poloxalene the animals are getting to reflect the bloat risk levels. It is also dyed red, allowing producers to easily see if it has mixed with the water.
New Liskeard Trial
During the alfalfa trial in New Liskeard, the researchers used several bloat management strategies. The steers were moved to a new section of alfalfa after lunch, which allowed the soluble protein levels in the plants to come down a bit. The steers were also on two forms of bloat control, as they were research animals and even one case of bloat would have been detrimental to the study. Each steer was given a Rumensin bolus and Alfasure was also used in the water. Alfasure was chosen over Bloat Guard to ensure each animal was consuming it. The study also called for 13 of the steers to just receive pasture, which would have made it harder for the researchers to get Bloat Guard into these animals. Even in the groups of steers that were supplemented with corn, top dressing would have been a poor option as there were steers that would not come and eat grain.
There are many advantages to grazing alfalfa that outweigh the risks of bloat (like an ADG of 1.9 lbs on straight pasture!), however each situation is different. Producers must look at their own operations and choose the method of bloat control that will work the best for them and their cattle. With a little effort grazing alfalfa is something that can be done safely with large returns coming back to the producer. However each situation is different and producers must access which method of bloat control will work best for them.
i Majak,W., Howarth, R.E., and Narasimhalu, P. 1985. Chlorophyll and protein levels in bovine rumen fluid in relation to alfalfa pasture bloat. Canadian Journal of Animal Science. 65:147-156
ii McMahon, L. R., McAllister, T. A., Berg, B. P., Majak, W., Acharya, S. N., Popp, J. D., Coulman, B. E., Wang, Y. and Cheng, K.-J. 2000. A review of the effects of forage condensed tannins on ruminal fermentation and bloat in grazing cattle. Can. J. Plant. Sci. 80: 469-485.
iii Berg, B.P., Majak, W., McAllister, T.A., Hall, J.W., McCartney, D., Coulman, B. E., Goplen, B. P., Acharya, S. N., Tait, R. M.,and Cheng, K.-J. 2000. Bloat in cattle grazing alfalfa cultivars selected for low initial rate of digestion: A review. Canadian Journal of Plant Science. 80:493-502
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