Hives and insect bites in horses
Hives from noxious weeds and Insect Bites...
MORE ON SKIN CONDITIONS (August article)
One of the more disturbing experiences we have is to arrive at the barn and see one of the horses covered in bumps. The horse itself may or may not act like it notices. These cases have been very common this year.
The horses presented to the clinic have knots all over their necks, chests, and usually the front parts of the body from the rib cage forward. The knots are so plentiful the horse appears to have been shot with buckshot! In more severe cases, the horse may be trying very hard to scratch the bumps to relieve the terrific itch. Others may be standing unconcerned, better able to withstand the torment of the irritation.
The cause of these bumps is usually insect bites. The horse either walked into a recent hatch or nesting place, and disturbed a large group. Rarely are they from bees or hornets. If the horse does walk into a group of these, they will often show other signs of reactions. These reactions may be seen as swelling around the eye lids, and if you care to check, swelling of the lips, and the vulva of mares. The knots in the latter areas are usually much larger and very painful. Breathing will usually be affected with flaring of the nostrils and rapid, shallow breathing. The body temperature will be elevated to 103° F, or more. If you suspect this is the condition, the case is much more severe and Dobbin needs to be brought into the clinic quickly!
There will occasionally be local reactions to vegetation as well. The horse will wander into a patch of briars or plants with sharp points or thorns. Each place these touch the skin a bump will appear.
For both of these conditions, the horse’s reaction may be limited to only one stage in the development of the plant or insect. As soon as this passes, the same insect will stimulate very little response. Of course, there is a difference in the response of each horse to the same exposure. Some will react with itching and swelling, while a herd-mate hardly notices.
Most of the time, there will be a very small scab in the center of the larger knot. This is the entry point where the insect stung or the plant stuck the skin. This is serum that has oozed out of the swollen knot. We will occasionally find the scab to be a very small tick, but this is only with the use of our dermatologic magnifying glasses!
By far the majority of the cases are in horses that have moved into the area within the last one to two years. They have not yet become accustomed to our brand of insects. It usually takes a year or more for their immune system to respond with protection. The incidence of this problem is always worse in the spring, when the bugs and forages reproduce with vigor and their numbers are high. We may very well see a duplication of this--if it ever rains again. We have had such dry weather this summer, the insects are even affected. After even a light shower there will be more, as if they have been resting in a dehydrated state.
Treatment is much as we would treat ourselves for hives. We use antihistamines (histamines are the substances produced by the body in reaction to the substances injected by insects: they cause inflammation, swelling, and accumulation of fluid), as well as moderate doses of steroids. The use of these medications will prevent swelling until the histamines clear from the system. They should be kept on hand for emergencies during the first year this horse is on the farm.
Prevention is a challenge. Diligent use of insect repellents will be a big help. Moving the horses away from infected areas will also help. Patience is also an asset, as this condition does eventually pass.
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