“Fog Fever” a Fall Pasture Problem

Clif Little OSU Extension, Guernsey County

Fog Fever is a rapidly developing, respiratory disease of cattle. Fog Fever is also called Acute Bovine Pulmonary Edema and Emphysema (ABPEE). Conditions and growth in our fall pastures has been perfect for this disorder to show itself. The onset of this disease occurs very quickly when hungry, adult cattle have been on dry feed or scarce summer pasture and are moved to green pasture or hay fields that are rapidly growing and lush. This rapidly growing pasture can be fescue, grass-clover mixture, alfalfa, or other annual forages. The key factors are mature cattle that have been in a scarce dry summer pasture for some time and moved to rapidly growing, lush green grazing area.

Cattle suffering from Fog Fever become affected shortly after the move to lush grazing usually in less than 10-14 days. Affected adult cattle will have a rapid onset of respiratory difficulty. Sick cattle may not want to move, grunt, breathe with their mouth open, froth at the mouth, and stand with their head and neck extended and elevated. Cattle may have a normal temperature, or they may have an elevated temperature (> 103). Bovine respiratory syncytial virus (BRSV) can be mistaken for “fog fever”. Contact your veterinarian for diagnosis and as soon as you see unusual symptoms in the cattle.

Fog fever appears to be brought on by an abrupt change in diet. As the diet changes so does the rumen of the cattle. When we move cattle from a summer pasture to a stockpiled pasture or hayfield there can be a significant change in the nutritional quality of the forage. It is this change to lush green pasture and the increased consumption of the amino acid tryptophan that seem to cause the adverse health reactions. The excess tryptophan in the forage is converted by rumen bacteria to 3-methylindole (3-MI) at an unusually high rate. 3-MI is absorbed through the rumen into the blood stream and circulated to the lungs. 3-methylindole appears to cause the toxic changes in the lungs of cattle. There is no antidote for “fog fever” and cattle may not respond to symptomatic treatment and may die within a couple of days. Avoid any unnecessary stress of sick cattle. Your veterinarian may prescribe Banamine or the use of ionophores such as Rumensin or Bovatec before turning the cattle onto the lush pastures.

There are some pasture management tools, which may help to prevent “fog fever”. Gradually introduce lush pasture to grazing livestock.. Limit the time animals can graze the new area and feed some hay before turning them out. Gradually increase the time on the lush pasture so that at the end of ten days you can keep then out. Another strategy would be to allow a lower risk class of livestock such as yearlings or sheep to graze the new pasture first. Rotate pastures more quickly so that there is not a large difference in forage quality.