PARASITE CONTROL  

 

 


 

 

Why do horses need to be dewormed?   

 

     Horses have been hosts to worms for ever.  Wild horses living on huge tracts of land are less susceptible to heavy worm infections simply because they are so spread out and constantly on the move.  Contrast this with our domesticated horses which tend to live on small tracts of land in more concentrated groups where they can easily come in contact with manure from their herd mates.  

     In the basic life cycle of  horse worms, the adult worms live and mate inside the horses's  intestine.  The females lay eggs which pass out in the manure.  The eggs are then consumed by a horse, hatch inside the horse and may undergo several life stages to eventually become adults in the intestine.  Some types of worms have a life cycle where the eggs hatch in the environment to turn into free- living larvae that are eaten by the horse to then turn into adults inside the horse.  Tapeworm eggs are passed in the manure and then eaten by a free-living pasture mite which the horse eats during grazing, and once inside the horse, the infective tapeworm larva develops into the adult tape worm.

 

 

What are the signs of worm infection in a horse?

 

     Infected horses may be thin, have poor hair coats, suffer from colic and foals may get pot bellied.  Pin worms may cause itching around the tail. Many do not show any external signs at all.

 

How can you tell if your horse has worms?

 

     You will not usually see adult worms in your horse's manure.  To determine the worm burden your horse is carrying, you need to have your veterinarian perform a fecal egg count in the laboratory using a microscope.

                                                      

What harm can worms do to horses?

 

     This depends on the life cycle of the particular worm species. Large round worms called Ascarids can get as large as a pencil.  Foals are particularly susceptible to ascarids and large accumulations develop causing pot bellies and severe or even fatal colic due to obstructions caused by huge masses of coiled worms in the intestine.   A smaller variety of round worm called a Strongyle has two types.  Large strongyle adult females lay eggs that exit in the manure, the eggs hatch and turn into infective larvae in the pasture and the grazing horse picks them up.  The larvae enter the intestine and burrow through the wall into the arteries supplying blood to the intestine.  They stay in the arteries for  2-3 months and while there cause a thickening and roughening in the artery wall which can obstruct blood flow to the intestine causing serious or fatal colic.  Small stronglye larvae are likewise eaten by the horse, except these larvae burrow into the wall of the intestine and form a cyst in the wall where they live for a few months.  While here, they may be responsible for inflammation of the intestinal wall causing diarrhea (especially in winter) and mild colic.  Female pin worms exit the anus and lay their eggs cemented in clumps around the anus and may cause marked itching.  Adult tapeworms live in the intestine and can cause a very serious and sometimes fatal colic due to intestinal damage and/or obstruction.   Bots have a little different life cycle. The adult is a medium sized fly you may see buzzing around your horse's front legs and head in the fall.  It has no mouth parts and cannot eat, therefore it lives only 4-5 days and must get it's eggs laid in that short time. The eggs are tiny yellowish eggs that the fly glues to the hair. The eggs hatch into larvae which find their way into the horses mouth and then eventually on down to the stomach where they attach to the stomach wall for almost a year.  In the fall they let go, pass with the manure and pupate and then hatch into a fly.

 

How can one reduce the risk of worm infection?

 

     Good pasture hygiene in the form of picking up manure in paddocks and small fields, and harrowing larger fields in the late fall to break up manure lumps to expose larvae to the elements is very beneficial.   Even with your best efforts at hygiene, you will need to use some pharmaceutical deworming products to further help control worm infections.  To date,  no herbal or organic products have been developed that are useful in parasite control in the horse.  What you use and when you use it are essential considerations when using deworming products.  Worms may develop resistance to dewormers over time.   Many products that used to be effective are no longer useful.  Unfortunately, some of these products are still widely sold by uninformed retailers.

     Even research scientists do not all agree on the best approach.  Some advocate using one effective product until it stops working due to development of worm resistance.  Others argue  that rotating between effective products will decrease the development of resistance, but the first group says it will hasten development of multiple product resistance.  (Similar to the situation with some hospital bacteria in humans) .  This is a very serious matter as illustrated by the fact that sheep parasites in much of the world are becoming  resistant to almost everything available.

 

What can we do to deal with the development of drug resistance on our farms?

 

     Veterinary parasitologists  have recently determined that a small percentage of the horses in a group shed  the majority of the worm eggs.  Most of the herd may in fact have developed pretty good immunity to the worms and may require less frequent deworming.  So how do we figure out who is a shedder and who is not?  Fecal egg counts give us that answer very well.  By doing a fecal egg count on all your horses, we can tell you which ones are the most serious shedders.   These ones should be treated and then another fecal egg count done in two weeks to see if the product used was effective.   Ultimately we want to identify the significant shedders  and  treat them appropriately .  The rest will still need periodic deworming but to a much lesser extent.  We can do a fecal egg count for about the same cost as a tube of dewormer.

     This may be a new concept for you. We feel it is everyone's responsibility to take the resistance issue very seriously.  It is a bit of work at first and will change how you spend your parasite control dollars, because rather than  buy dewormer for every horse every 2-3 months, you will need to be spending some on fecal egg counts.  Once we identify which of your horses are the main shedders, you can then direct your time and money to treating only those that need it.    Our goal is to properly treat the shedders and decrease the treatment of  non-shedders, thereby  preventing or at least slowing  the development of parasite resistance.

      Equine deworming products are available from on line, to feed and tack stores and veterinarians.  Some of the products are excellent, but some are no longer useful and some from generic manufacturers are of questionable content.    We dispense only name brand products that are backed up by the manufacturer.  Our  product prices are competitive and we'd like to be able to put together for you a program that effectively controls the parasites in your horses, reduces chances of resistance, and likely will end up costing you less than you presently spend on parasite control.   Most importantly, it will be better for your horses.

     Learn more about how to implement this new program for your various horses by reading the pertinent section on this site.