Extension Education: Bloat: A Forage-Related Animal Disorder

Animal disorders may result from toxic substances or mineral imbalances in forges and weeds consumed by livestock. As a result, reduced animal productivity, such as visible symptoms of ill health or even death of grazing animals, may occur.

Bloat is one the important animal disorders. 

This can cause a serious problem in cattle grazing pastures dominating by certain legumes. Cattle are more susceptible than other ruminant and non-ruminant animals. The cause for bloat is the formation of stable foam in the rumen that prevents eructation or belching of gases produced by the microbial fermentation of forages. As a consequence, gases lost by eructation are retained and the left side of the rumen then increases. The oxygen supply is then reduced, and it causes suffocation.

Because of the retained gases in the rumen and suffocation, affected animals swell rapidly, and in severe cases, death may occur within an hour. Susceptibility to bloat differs animal to animal. However where there is a chance of danger from bloat, the chronic bloaters should be removed from pastures.

Clovers, both white or ladino clover, and alfalfa are good examples of legumes that can cause bloat. 

However, there are some legumes that have less potential or do not cause bloat. Examples of some non-bloating legumes include birdsfoot trefoil, sainfoin, crownvetch, cicer milkvetch, sericea lespedeza, annual lespedeza, arrowleaf clover and berseem clover. These legumes contain high tannins in their plant cells, which act as protein precipitants to aid in breaking up the stable foam formed in the rumen. 

Bloat may also occur on lush pastures of ryegrass or small grains, especially in the spring. Beef cattle in feedlot-fed high grain diets with or without legume forage have less potential of occurring bloat.

It is not recommended to turn hungry cattle into a lush legume or winter annual grass pasture. Rather, producers would be better off to feed cattle with dry hay before allowing them to graze this type of pasture. Also, cattle should not be placed on lush forage wet with dew or that just received a frost. Limiting grazing and feeding with hay during early grazing can also reduce bloat incidence.

Grass-legume mixtures also reduce bloat potential. A mixture of 50 percent grass and 50 percent legume can greatly reduce the bloat hazard. Quick access of cattle to salt and water sources is helpful as well. Providing salt-molasses blocks containing surfactants, or detergent type compounds, can also reduce bloat potential, but these are relatively expensive.

It is highly recommended that cattle should be checked frequently during grazing, especially grazing with legume pastures. If a first sign of swelling of the left side of an animal is noticed, cattle need to be removed from the pastures quickly. Remember, bloat potential is greatest in spring when the plant growth is rapid compared to summer growth.

Anowar Islam is an assistant professor and the University of Wyoming Extension Forage Agroecologist in the Department of Plant Sciences in the College of Agriculture and Natural Resources. He can be reached at 307-766-4151 or mislam@uwyo.edu.