However, as with any medication, questions have arisen about the
effectiveness and safety of Strongid C, as well as the possibility of parasites
developing resistance to the medication. Several studies have shown that
Strongid C does work well, meeting the claims of its manufacturer for
reliability and safety, but many veterinarians are still cautious about the
Pfizer states that the daily dosing not only prevents adult worms from
developing within the horse and causing damage to internal organs, it greatly
reduces the amount of worm eggs which are shed in the horse's feces. This
greatly reduces the risk of other horses in the same pasture being exposed to
Strongid C treats worms as a condition to be continuously prevented, rather
than allowing an infestation to develop between occasional treatments. While
Strongid C is the first preventative deworming medication developed for horses,
it offers no protection against bots and onchocerca. Pfizer recommends
administering invermectin no less than twice a year to control these parasites,
in addition to the Strongid C. They recommend the invermectin treatments in late
fall or early winter, and once again in spring.
But is it worth the cost of Strongid C when invermectin is still needed?
According to Pfizer, it is. The continual protection offered by Strongid C
compares favorably against the paste dewormers which only occasionally purge the
horse's system. They maintain that horses are at high risk of parasitism due to
the shared facilities and pastures of most horse stables and ranches, and the
detrimental effects of parasites are greatly reduced when parasite control is
While paste dewormers which purge the horse's system are effective in ridding
the horse of worms at the time of treatment, they do not address the overall
effects of parasites. Horses which are treated with conventional anthelmintics
are immediately vulnerable to reinfestation as soon as the medication clears the
system, within a few hours or, at the most, a couple of days.
Can this daily deworming treatment protect your horse if it is pastured with
horses who are untreated, or only dewormed periodically?
One study indicates that it can. Mares treated with Strongid C showed reduced
numbers of eggs when contrasted with mares treated with a twice-monthly
deworming paste containing ivermectin, pyrantel pamoate and oxibendazole. Both
groups were tested at six weeks.
Strongid C is not an inexpensive treatment, running approximately fifteen
dollars per month per 1,000 pound horse. However, the reduction in the parasite
burden and its resultant gut inflammation can increase the horse's digestive
efficiency. This can reduce feed costs by up to ten to fifteen percent per
Many owners and veterinarians have found Strongid C to be a useful
medication, especially for horses with a history of recurrent parasite
infestations. No dewormer is one hundred percent effective, and Strongid C is no
different in that regard. It's not inexpensive, but its preventative value and
the reduced feed costs can make the expense worthwhile.
For owners of problem horses, Strongid C might be worth considering. However,
it's important to remember that no single product can completely cure every
situation, and you should always consult your veterinarian and read all the
label directions carefully before changing medications.