Sunday, June 3, 2018

Re-Thinking Deworming Strategies

As is wont to happen, each year our mature horses get another year older. We are also raising foals. Foals plus older horses create a perpetual parasite factory. Both the very young and many old horses do not have the quality  of an immune system that the majority of healthy adult horses have. Hence, they become incubators of parasites.

Of course, it is both a ridiculous and counter productive effort to seek to drug horses so often that they have fecal egg counts of zero. But parasites need to be managed for a variety of health reasons. One of those reasons often escapes the eye of the uninformed horse owner. Simply increasing calories, especially if those calories are primarily simple carbohydrates (as in sweet feeds) will do little to help such ancillary problems associated with a heavy parasite load as anemia.

One must also be concerned with the creation of parasites that are drug resistant. That is why the old idea of rotational dewormer use along the lines of the out dated protocol of the 1990's creates such a threat to the future of equine health.

I have always been leery of using Quest dewormer. I worried about the stories often told of the tremendous danger of overdosing horses with the drug contained in Quest. Even if the risk was small, ivermectin was cheap and within twenty four hours generally produced dead parasites in manure piles.

But I was constantly vexed by the problem of several herd members that have been hard to keep weight regardless of when they were dewormed and what they were fed. In recent years our protocol for such horses has been a thorough deworming and movement into a small pasture where they are fed hay and a highly digestible, low sugar, 12% protein extruded feed that is supplemented by a significant amount of gradually increasing vegetable oil. Most promptly begin to put on weight. Those who have dental problems are floated. In very rare cases, the floating helps. Primarily as a result of their forage based diet, few of our horses develop dental problems and the concept of constantly grinding away perfectly good teeth on a horse with no dental problems what so ever because the horse "is due for a floating" is ridiculous beyond consideration.

Completely unnecessary routine floating to prevent dental problems makes no more sense than putting a cast on an unbroken arm twice yearly to prevent broken arms.

Experience, observation and research matter in developing solid health protocols for your horses. Early this spring I stumbled into something that I wish I had truly understood years ago. I dewormed a three year old mare with fenbendazole. I had never been impressed with the results that I got from fenbenzadole and the results were no different this time. After twenty four hours there was minimal evidence of dead parasites in the manure. I decided to see what a follow up with ivermectin would do. The result was substantial evidence of effectiveness the next day. So I followed up with ivermectin two more days in a row. She continued shedding parasites.

There have been no indications of any side effects. I do not recommend following the experiment that I did. In fact, it is important to keep in mind that I am not a veterinarian. Advice on developing a deworming protocol or any other equine health protocol should only come after discussing the options with an experience veterinarian. I am not offering veterinary advice.

This experience, coupled with a discussion with my vet, cause me to reexamine my views on using Quest. While we might be experiencing some drug resistance to ivermectin I do not think that that has been the primary reason that it has appeared less effective in some of our horses. Ivermectin is a highly effective on parasites that are not encysted (with the major exception of tapeworms which it no effectiveness  against). However, it seems that a horse with encysted parasites releases them into the cecum and intestine, allowing them to pass on eggs and complete their life cycle, when their is a significant die off of non-encysted parasites.

The drug in Quest kills both encysted and non-encysted small strongyles. Quest is going to become a major part of our parasite treatment program.

I understand that a double dose of fenbenzadole, for five consecutive days works as well for many horses as a single treatment of Quest. The price and convenience of Quest makes that an attractive option for our horses.

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