How to End the Bot Fly Cycle, why Rhino...
SEASONAL REMINDERS FOR THE BROOD MARE
Fall brings plenty of reminders for horses, but since mares are carrying the future of the horse world, we will write the first article for them. Many of the reminders for the mare apply to all horses.
With the temperature creeping lower each day, the bot fly is eventually going to give up. Every year we announce the demise of this pest only to have one buzzing around our patient’s legs the next sunny day. This small fly resembles a honey bee with a fuzzy tail that curves in under its thorax. While it does not actually bite, the horse that is the object of its attention acts like the bot fly is going to chew its leg off. Fly repellents are of little use and it takes a steady hand and a quick eye (or a quick hand and a steady eye) to knock one out of the air.
The bot fly’s sole purpose in life is to complete its life-cycle. They efficiently do this by laying many small yellow egg packets on the hair of the front legs and chest of every horse within flying range. Horses from some farms have many more egg packets attached than horses from other farms, and dark horses will have many more than the lighter colored ones. The fly will continue infesting your horse until freezing weather stops them. The resulting larva are comfortably tucked within the efficient egg packet until stimulated by the nose or tongue of the host horse. This warm, wet, rough surface stimulates the top of the packet to spring open, releasing the larva within. This larva literally springs out of the packet onto the tongue or lips. It will begin migrating through these tissues on its way to the stomach. Once there it attaches to the linings and develops into a grub. If enough are present they will line a significant part of the stomach wall, interfering with digestion. The more active ones also have the potential to penetrate the lining of the stomach and allow drainage into the peritoneum. This can lead to a terminal infection.
Once the grubs are mature, which also coincides with the arrival of spring, they release from the stomach lining and are passed with the stool. Once on the ground, they hatch out of the grub stage as a small fly and start the cycle over again.
After the first hard freeze, we have the opportunity to break this cycle. By deworming the horse with medication that kills the grub phase, the cycle will stop right there. By eliminating the grub phase, the only bot flies around next year will be from the neighbor’s horses (if they have neglected to deworm). The indicated medications are the organophosphate insecticides or the ivermectin products. The ivermectin products are the most popular and are available under a variety of brand names. To prevent re-infestation after deworming, we must also take care of the egg packets. As we described, all it takes to hatch them is a warm, moist, rough surface. At the time we deworm the horse we should take a rough cloth or sponge soaked in warm water and wipe down the area infested with the egg packets. This will hatch the larva and prevent them from continuing the cycle. Of course, you must believe the above story about the larva hatching, because the egg packets will still be on the horse’s hair long after the larva are gone.
The vaccination most important for the pregnant mare is for the rhinopneumonitis virus. This very common virus is the cause of respiratory infections in all horses, but in the pregnant mare it invades the uterus and disrupts the placenta. This infection will lead to abortion between the seventh and tenth months of pregnancy. To prevent the abortions, we start vaccinating the mare in the fifth month and repeat it at seven and nine months. The vaccine must be the "Pneumobort" brand, the other brands will not stimulate immunity in the uterus. Most horses have already been exposed to this virus, and some will remain carriers. Unless having foals this spring is not that big a deal for you, inoculation of the pregnant mares is of utmost importance.
CLICK BELOW TO DISPLAY A PRINTER-FRIENDLY COPY OF THIS ARTICLE
Select "Open this file from its current location," if you just want to print it out,
it will open in a simple word processing application, select the print button.
(unless you want to save this article in your computer's memory)
