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West Nile Virus Info

Equine and West Nile Virus

          Since the outbreak of West Nile Virus (WNV) in 1999 there have been approximately 24,000 confirmed cases of horses infected with WNV in the United States and Canada.  Of these cases there is a 1 out of 3 mortality rate.  With birds being the main carrier of the disease and mosquitoes being the transmitter, it has spread rapidly throughout the United States and in 2002, Canada.  Health officials have been warning people to find any sources of standing water and remove it so the mosquitoes will not be able to reproduce.  One possible source is the large open stock tanks that livestock, including horses, drink from.

          Large stock tanks in the pasture are the perfect breeding ground for mosquitoes.  The volume of water in these tanks can range from 50 gallons to 1,500 gallons or more.  Many of these tanks are filled automatically with an attached float and valve so that even though horses are drinking out of the tank, the water is never completely drained thus allowing for the "egg to hatch" cycle of a mosquito to be completed.

          Birds are attracted to these tanks as well; if they are infected, they can pass the WNV to mosquitoes where they breed.  Because mosquitoes tend not to travel far from where they are born, it is very easy to see how a horse can be a victim of WNV.

          Studies have shown that when the surface of water is disturbed the larvae of the mosquito will swim to the bottom of the water tank.  So even though a horse may be drinking, the mosquito larvae will not be removed from the tank at that time.  And in a large tank of water, the agitation of the water created from the automatic valve is not enough to disturb or remove the larvae.

          It is being recommended that these large open tanks be drained and cleaned every third day to break the "egg to hatch" cycle of the mosquito, this can be cumbersome, time consuming, and a waste of water.  However, there are some good alternatives to large open stock tanks that will greatly reduce to eliminate mosquito breeding in your horse's source of water.

         The first choice is an automatic waterer where the surface of the water is completely covered at all times so that mosquitoes cannot lay their eggs.  These waterers have a ball or elliptical float that the horse pushes down to get to the water.  The elliptical float tends to work much better for horses because the balls are hard to push down and have to be pushed a long distance before the horse can get to the water.  When the horse is done drinking these balls jump back at the horse causing the horse to be tentative about drinking.  The elliptical disc however, like the ones used in Ritchie Industries CT units, are designed to take little pressure to move.  They only have to be moved or tipped a small distance, and does not jump back at the horse.  These waterers are made of tough polyethylene plastic that can withstand a lot of abuse and because of the slick surface are very easy to clean.  They tend to be well insulated and in most cases when installed to the manufacturer's recommendations, will work throughout the winter without any other source of heat.  In the summer they will keep the water cooler and reduce or eliminate any algae growth that is typically seen in the large open stock tanks.

          One word of caution here.  When looking at this type of automatic waterer, remember, you get what you pay for.  There are some cheap waterers of this type on the market that tend to be poorly constructed, have little insulation and are not sealed so the insulation becomes saturated with water and loses it's insulation properties.  Also, the plastic tends to be thin and will not stand up to this type of environment.  The better automatic waterers of this type are more expensive than an open stock tank, but in comparison to a lost horse, it is a good investment.

          The second alternative is to install an open surface, automatic waterer that has very shallow water and a quick fill valve.  In this case the shallower the better as long as the valve can replenish the water quickly.  These waterers will hold as little as 2 gallons at a time and can water up to 40 horses.  They are constructed out of plastic, stainless steel, or a combination of both.  They are easy to clean and because of the shallow water and the agitation caused by the high fill valve; it is difficult for the mosquitoes to use this as a breeding area.  Again, the same rule of "you get what you pay for" applies here as well.

          In February 2003 the US Department of Agriculture (USDA) fully licensed a WNV vaccine for horses.  Although there has been some skeptcism about the side effects of the vaccine, it has proven to save many.  The use of an automatic waterer, covered or open, that is easy to clean and features a small amount of standing water, alone or in combination with the vaccine can greatly improve the protection of horses.

          Finally, we have to keep in mind that while we are trying to protect our horses from WNV, we are trying to protect our families, friends, and ourselves as well.  So take a hard look at how you are watering your horses and livestock and consider installing an automatic waterer that will help reduce the spreading of this terrible disease.

          Ritchie Industries, manufactures a variety of fountains that fit this description.  Please visit our website or contact 866-534-7492  for more information.

Sources:  Animal and Plant Health Inspection Service Website,

               Centers for Disease Control and Prevention Website