MSU Extension

Ruminant grazing animals are at risk to bloat any time during the grazing season but early fall is one of the more risky times. For cattle, sheep, goats and other ruminant animals, bloat can either be persistent, but nonlethal, or it can appear suddenly, leading to death with little warning. Pasture bloat, commonly called frothy bloat, is caused when slimy foam builds up in the rumen preventing normal gases from being released by the animal via belching. This captured gas enlarges the rumen like a big balloon applying pressure on the diaphragm lining that separates the digestive tract from the heart and lungs. The bulging diaphragm, in severe cases, can pressure the lungs and heart restricting breathing and blood circulation leading to death. In pasture situations this froth often forms when ruminant animals consume highly digestible forage in rapid fashion.

Legumes, such as alfalfa, ladino clover, red clover, kura clover and white clover in the vegetative stage of growth have high soluble protein contents and are commonly the cause of frothy bloat in pasture situations. Oddly, birdsfoot trefoil which is also a legume commonly found in the Northern States does not cause bloat. It is believed that tannins found in trefoil break up the foam preventing frothy bloat. In areas where winter wheat grazing is common, bloat can occur in cattle grazing immature, lush wheat - so legumes are not the only cause.

So what is a manager to do; avoid planting bloat causing legumes completely or only plant birdsfoot trefoil as a pasture legume? Alfalfas and clovers are some of the most productive pasture legumes for the northern states that will take multiple grazings in a summer season and still persist for future years. They produce free nitrogen from the air that stimulates grasses to grow better. With good grazing management these legumes can still be utilized to maximize animal performance without experiencing the impact of bloat.

To manage ruminants on pasture to prevent bloat, we must first be aware when bloat is most likely to occur, and then know what to do to manage the risk. The risk of bloat is highest when:

Pastures are made up of 50% or more of the legumes listed above that cause bloat – When planting or frost seeding follow recommended seeding rates; select varieties that will mature close to the same time; in dry periods delay grazing until soil moisture returns allowing the grasses to catch up to the legume growth; feed a bloat guard block or long stemmed hay if you must graze a high percentage legume pasture; or as a last resort consider spraying a herbicide to knock the legume content down

Hungry animals are first turned into a new paddock or pasture – The greatest danger is the first day they are turned into something new, as the soluble protein content of the legumes will be at their peak and the animals will consume it rapidly because they may be hungry. To avoid this, either do not over-graze the previous paddock by leaving at least five inches of stubble, because as the lower they graze below five inches, the less they will be able to consume and the hungrier they will become for the new forage; or feed some hay or other fibrous feed before turning them in, so they are not hungry and their rumen is full.

Pastures are wet from dew or from rainfall at turn in – Wet pasture seems to increase frothy bloat at turn in, so always let the moisture burn off first.

Alfalfas are in the vegetative stage and have not reached blossom – soluble protein content of alfalfa is highest at early growth stages and decreases as the plant matures, so especially in mid-summer and fall grazings when grass growth slows and the alfalfa portion in the sward approaches 50% or more, let the alfalfa reach maturity by being in at least 25% blossom before grazing

Animals are given large areas to graze that take over a week or more to graze down – Anytime the legume portion of the pasture is high, or for some other reason the risk of bloat is high, decrease the size of the pasture unit with cross-fencing, as without it, grazing animals will often roam the entire paddock top grazing only the top leaves and stems of the plants, which are the highest in solubility. If given a smaller area, they are forced to eat down into the portion of the plant that is less digestible sooner, reducing the risk of bloat.

Animals are turned into legume pastures after a frost – Frost on legume pastures tends to break down plant cells in those plants increasing the risk of frothy bloat. As the fall season approaches, take extra precautions mentioned previously or try to save the grassy paddocks for fall grazing.

When the animal’s diet is 100% pasture based – Anytime we can dilute the pasture portion of the diet with small amounts of hay, haylage, corn silage, or even grain, when properly balanced in the diet, we diminish the risk of bloat. Proper mineral and water consumption is also determined to help reduce, but not eliminate, the incidence of bloat, as is the feeding of an ionophore in a mineral or feed source.

When bloat is discovered, there may be little time to seek professional help. Speak to your veterinarian and obtain the proper tools and treatments for bloat. Have them on hand before bloat occurs, so you can act quickly if necessary. There are feed additives, blocks, and drenches containing bloat inhibitors that can be used as a preventative measure. They however can be time consuming to administer and will add extra expense to your bottom line.

Grass based pastures with approximately a 40% legume mix of clovers and/or alfalfa should still be the goal of most beef, goat, sheep, and grazing dairy farms. These pastures are still the most economical choice for these farms to feed their herds and flocks in the growing season. The risk of bloat is real, but with proper knowledge of its cause, with proper knowledge of how to prevent it with good pasture management, and with proper preparation of what to do if it appears, it can be a minimal risk.

For more information, contact Michigan State University Extension Grazing Educator, Jerry Lindquist at lindquis@msu.edu or 231-832-6139.