Now, the animals have been stepped-up to the high-grain diets and they are close to their maximum intake capacity. We have already overcome the plague that respiratory diseases are in those newly arrived. Also the stress of the first days on feed, diarrhea, lack of appetite and hopefully deaths associated with newly arrived cattle problems are past history. Then we are ready to take advantage of the already transitioned digestive tract environment (rumen bugs are adapted to the presence of grain and digest it efficiently) and we are ready to start putting weight on these animals… however, one more hurdle needs to be jumped: feedlot bloat.

What is feedlot bloat?

In simple terms, feedlot bloat can be defined as a disruption in the rumen function that promotes the formation of stable foam impairing the normal elimination of the gas produced during the digestive processes. The consequences of feedlot bloat can range from a minor reduction in feed intake to sudden death by impaired respiration resulting from the pressure from the expanded rumen on lungs and diaphragm.

Even though the obvious impact of feedlot bloat is an increased mortality, cattle death is not the only economic loss. Perhaps the greatest impact of bloat on feedlots’ profitability is due to reduction in animal performance (reduced intakes), increased culling due metabolic disorders and increased treatment costs of bloaters.

What causes feedlot bloat?

Feedlot bloat can be caused by several factors and the interaction of them. Typically feedlot bloat is associated with the intake of large amounts of grain, specially those types of grain that ferment rapidly in the rumen such as wheat or barley. Even though the presence of large amounts of grain in the diets is a triggering factor, management and animal factors contribute to the development of bloaters. When the grains enter the rumen they are fermented by the rumen microbes producing large amounts of gas. Normally those gases are released by waves of rumen contractions followed by eructation, but under certain conditions such as: excessive amounts of gas produced, reduced rumen contractions, obstructions in the upper gastro intestinal tract, etc, bloat can occur.

Contribution from the rumen microbes cannot be ignored. The viscosity of the rumen fluid can be increased by the formation of slime by the rumen bugs, which will contribute to the formation of stable froth. Proliferation of certain types of microbes in the rumen triggers the produce of slime, and those types of bacteria are usually the ones that grow fastest under high-grain diets. This serves as another example (besides the excess production of gases) of how high-grain diets can prompt the incidence of bloaters.

Types of feedlot bloat

Bloat can be classified in two types: free-gas bloat and frothy bloat. Free gas bloat is of rapid onset and often lethal. The animals presenting free-gas bloat usually die suddenly as a result of an obstruction in the esophagus impairing the elimination of gases. These obstructions can be caused by undigested feed particles or partially chewed feeds that can block the esophagus. Free-gas bloat can also be caused by chronic pneumonia or hardware disease as they may affect rumen motility by damaging key nerves involved in those mechanisms. Free-gas bloat can be relieved by removing the obstruction or making a rumen fistula (minor surgery creating a hole from the rumen to the outside) allowing gas escape. Free-gas bloat does not happen as frequently, but its often lethal consequences sure gives them more press than frothy bloat.

Frothy bloat is the most common type of bloat and rarely leads to death. Animals with frothy bloat present a stable mix (bubbles) of gas and liquid at the top of the rumen that traps feed particles and prevents gas release. In frothy bloat caused by pastures, legumes such as alfalfa or red clover are responsible for the formation of stable foam. In the case of feedlot frothy bloat the responsible agents for the formation of foam are the rumen microbes.

Even though feedlot bloat has been associated with acidosis, resulting from high-grain diets and intake variations, both types of metabolic disorders can occur independently from each other.

How can we prevent it?

The causes are complex and often hard to predict. The use of grains has been indicated as the factor always associated with bloat; however, reducing the amount of grain to be fed is usually not an option, as animal performance would be reduced. Fed management strategies are probably the most common and cost-effective tools to prevent feedlot bloat.

Replacing the use of highly fermentable grains in the rumen such as wheat or barley in finishing rations for other sources such as corn is a viable alternative. Also the processing method will play a key role in bloat prevention as may limit the amount of starch that will be degraded in the rumen. Whatever is not digested in the rumen does not mean that will be wasted. The small intestine still will use part of that starch without risk of bloat. In general, the smaller is the particle size of the grain, the greater the chances of developing bloat, as more surface will be exposed to the microbes for digestion.

Feed additives such as ionophores and bloat preventives have been widely used. Ionophores such as monensin and salinomycin prevent bloat by inhibiting specific types of microbes or reducing feed intake. Bloat preventives such as poloxalene are most commonly used in pasture bloat and are low-foam detergents that reduce foam stability in the rumen.

In summary, bloat is a metabolic disorder that can harm the economic success of your beef operation; however, a set of tools, management practices and good amount of information are available to prevent or minimize feedlot bloat incidence and enhance animal performance.