Rearing period of young horses sets the basis for worm susceptibility

The influence of the rearing period is extremely important for the susceptibility to worms. Foals from mares who have had worm problems during and after pregnancy automatically face a higher level of worm infestation. Foals eat their mother's feces to build their intestinal flora, if this feces is infected with a higher amount of worms, the foal is immediately exposed to an infection. It is therefore extremely important to be very precise with worm examinations and deworming in the first years. Of course, all horses are exposed to worm infestations and that's OK, but the infestation must be high enough for the horse to build resistance and low enough not to cause any problems. The horse must establish a symbiosis with the worms.

If your horse is in a rearing facility, be critical of the management. For example, ask if the pastures are cleaned instead of spreading the manure across the pasture. Spreading manure in pastures increases the chances of reinfection in young horses. A group of young horses that may not have built up enough resistance to worms should be closely monitored.

One horse has a better immunity than the other horse

Horses that have grown up without problems, have not had any intestinal issues, and have not been exposed to large amounts of worms, will naturally have a greater resistance to worms than other horses. This is a natural trait where we as horse owners can't do much except provide a good foundation. By a good foundation, we mean nutrition, housing, and access to other horses. Nutrition is one of the most important aspects, because for worms you want the intestinal wall to be thick enough so that any worm eggs cannot encapsulate. Unprocessed roughage and limiting grains are important here. But do not underestimate the fact that the first years are crucial for building resistance to worms and this can really make a difference in the resistance between your horse and other horses in the boarding stable.

And finding a worm occasionally in the feces is not a problem!

Resistance to worming agents

In the past, horses were dewormed every 3 months as a standard practice and this is probably still being done in many places. But the overuse of worming agents has led to a lot of resistance to dewormers. For example, roundworms have become resistant to ivermectin. Not all agents are effective against all types of worms. It is very important to choose the right wormer for the specific type of worms. A major factor contributing to this is that horse owners often underdose, underestimating the weight of their horse so these horses don't receive enough dewormers. This allows the worms to survive and develop resistance to the active ingredients. When deworming your horse, always give a sufficient amount of deworming agent.

Deworming every 3 months is not recommended. It is better to follow the Worm & Co schedule and use fecal tests. Based on these tests, you will know which type of worms may be present in the feces and which dewormer is best suited.

Is your horse susceptible to worms?

If so, make sure to regularly test your horse's feces. Nowadays, this can be done through almost any veterinarian, but also through Worm & Co, for example. Based on these test results, you can deworm specifically and ensure that the worms are kept under control.

Try to keep the infestation as low as possible by cleaning pastures and paddocks at least 3 times a week. Sheep in the pasture are also an option to eat the plants that the horse does not consume, and to prevent reinfection with worms. Consider giving liquid nettle tincture four times a year to support the intestines and keep the immunity optimal.

Also important to note, horses build resistance to worms in their first 5-6 years of life. Usually, after this age, worm infestations stabilize and worm problems decrease.

From personal experience:

The horse of our customer service representative Marjolijn is a mare who hardly ever has issues with worms. This mare had a good start in life and naturally has an extremely strong resistance to worms. This mare is kept together with a young gelding who almost always tests positive for worms, unfortunately, this gelding had a rough period during rearing and experienced a lot of intestinal issues. The manure is removed daily from the paddock and the pasture and a lot is done to keep the gelding's resistance optimal.

Despite the fact that the gelding's manure often looks like spaghetti (despite a deworming protocol in consultation with the vet), Marjolijn's mare consistently tests negative for worms.

So, it certainly does not have to be a problem if your horse has a negative fecal test compared to a horse with a positive test. It all depends on the individual horse's immunity!