Drug resistance has been an important topic in the medical community for many years.
We’ve watched as simple bacterial and fungal infections have become resistant to common antibiotics. This resistance is equally concerning in the horse world in the treatment of infections and the realm of parasite control.
Many horse people live by the policy of deworming every three months and rotating drug classes with the theory of covering the entire parasite spectrum. In theory it sounds good; however, this overuse of anthelmintics is leading to the ineffectiveness of several drugs in many parasite types.
We need to start deworming intelligently. This starts with taking fecal samples and having egg counts done. Any veterinary clinic can do or have this done for you. Some choose to send them out to labs while some will do them in house. Call around for prices and availability. In house is around $20-$25 while those being sent away will likely incur shipping charges.
It is believed that roughly 20 per cent of the horse population carry roughly 80 per cent of the parasite loads. The best place to start is by identifying the heavy shedders in your herds. Testing all of your horses will indicate where to begin. Horses who are low shedders may only require being dewormed once or twice annually while heavy shedders will require more frequent treatments. Over 500 eggs/gram is considered a heavy shedder. Two weeks after deworming, you should retest. You are looking to see a minimum of 80 per cent decrease in the egg count. If this is not the case then your parasites are resistant to that drug type and you need to try something different. If a drug type is effective, then stick with it! Retest after a period of time to watch for the egg counts to rise (called the egg reappearance period) this will indicate when the horse needs to be retreated. This recent research is showing what is extremely evident in human medicine. The overuse and misuse of drugs lead to resistance. Rotational worming programs have been the “norm” for many years, but are now being found not necessarily as effective as once thought.
Use what works — that will be proven by the follow up fecal exam two weeks after administering a treatment. Don’t just rotate randomly through the available list of drugs, be sure to evaluate the fecal eggs counts and customize to what is required.
The initial investment required to map out your deworming program should be quickly offset by the reduced amount of product you will require to purchase. I am not saying to stop taking care of your horse, I am just encouraging you to only deworm when needed and using what works rather than blindly administering unnecessary drugs. In time the financial investment will pay off.
Horses naturally chose to not graze where they defecate. Overcrowding and overgrazing are substantial factors in the infestation of horses. Picking up manure (you’ve heard me say this before!) is as effective in bringing down egg counts as worming and far more natural. Proper composting (complete with turning) creates steaming heat and heat will kill many parasite eggs. When your horse lives with other horses, your deworming program is only as good as the worst one in with your horse. Co-ordination is required to be effective and successful.
All horses have parasites. Small worm loads are not going to hurt them. Where you start to run into problems is when horses are overcrowded, nutritionally deficient or under excessive or ongoing stress. This decreases the effectiveness of the immune system leaving the horse vulnerable.
Studies show that horses which are dewormed frequently are more susceptible to infestation and others potentially linking the increase in allergies and autoimmune issues to the lack of parasites in some horses. It will be interesting to watch the future research in these areas.
In Alberta, spring is when the transmission period begins. This typically continues until the first freeze in the fall. Worming during the winter is considered unnecessary unless there are signs of parasitic disease. These symptoms include poor coat, weight loss, lethargy, anemia and generally poor health. A veterinarian should be contacted to evaluate an unthrifty horse as worming a horse with a heavy parasite load could lead to colic or other problems. Deworm by weight not by the tube. It’s a shame that Eqvalan is no longer available in its liquid form. This product was a cost effective way to deworm accurately for every weight of horse.
Shelly Graham is a local rider, trainer, horse breeder and Equine Canada certified coach.