Ask the Vet: External Parasites

Answered by: Carolyn Simmelink, DVM, Redding, CT Courtesy of AAEP

Question: Can a dry lot be sprayed with something that will kill ascarid larvae in order to prevent reinfestation?

Answer: I am not aware of a spray that works but dragging the paddock with a harrow in dry weather and sprinkling lime on the favorite defecation and urination areas works well to kill parasites.


Question: How well do you feel the feed-through fly pellets work? I have been using them this summer with what appears to be success. I only have two horses and no other livestock.

Answer: The feed-through fly pellets are very effective as they stop the fly reproduction at the source Рmanure.


Question: Insects distract my mare so much that she becomes difficult to ride. Is there anything that would help her cope with bugs?

Answer: I spray an ear bonnet that goes under the bridle just before I ride in addition to spraying the rest of the horse. I recommend a spray that is labeled to repel mosquitoes and gnats as well as flies. I also carry a tail switch this time of year so that I can shoo the bugs away that the horse cannot reach with its own tail. A fly mask and nose net help some horses that are particularly bothered about bugs near their face.


Question: Is it safe to use a long lasting topical spot treatment on a horse as well as a pyrethrin based spray when riding? My horse spends a lot of the day in his pasture when I am not riding him.

Answer: I use equispot on my horses twice weekly during tick season in the northeast and fly spray daily during the summer for years and have not had any problems but that is my own personal experience. I am not aware of any scientific studies to test this.


Question: My horse is experiencing lots of bites on his neck and back. Does apple cider vinegar in water or feed help to distract bugs?

Answer: It might help but that alone is usually not sufficient. Changing the time of day that a horse is turned out or wearing a fly sheet can be helpful. Large welts on the back or neck are usually horse flies and they are most active in the daytime in the sun.


Question: The mosquitos are horrific this summer making it miserable for our horses. I rub them down with a permethrin based product in the AM and PM but it only gives them temporary relief. Some evenings, the horses’ faces and necks are swollen with welts. Is there anything we can do to protect our horses?

Answer: Mosquito prevention is best achieved by clearing up any standing water. This includes cleaning gutters and dumping buckets and troughs at least twice weekly. There is a product called Mosquito Dunks that can be used as directed in areas where the water cannot be dried up such as drains and low lying ground. Bats and barn swallows are our friends in this battle so encouraging their residence near the barn is helpful. The mosquitos are most active in the evening and avoiding turnout on grass at that time could also help. Deet is the most effective repellant but should not be used on the horses skin directly but it could be applied to blankets or ear bonnets.