Both paste and pellet equine dewormers are given to horses based on weight. For that reason, it's important to weigh your mini, using a weight tape, before giving him any sort of dewormer. On average, miniature horses weigh about 200 pounds. While many dewormers allow for a wide margin of error in dosing, some do not, and the results of giving your miniature horse too much wormer can be serious.
The American Association of Equine Practitioners recommends having your vet perform fecal eggs counts on your minis before deworming at the start of the season. Bring a few balls of fresh manure to your vet for testing. Based on the number of worm eggs in the sample, your vet can recommend a deworming protocol for your little horses.
Moxidectin and Miniature Horses
Moxidectin is a broad-spectrum dewormer, marked under the name of Quest. Moxidectin with praziquantel, a dewormer that kills tapeworms, is marketed under the name of Quest Plus. The manufacturer, Zoetis, warns that "extreme caution" must be used if giving these products to foals or young equines or miniature horses. That's because there is no "wiggle room" in dosing moxidectin -- the animal must receive the correct dosage for his weight.
Zoetis notes that overdosing may result in "severe adverse reactions." For that reason, many veterinarians do not recommend giving moxidectin products to miniature horses, period. While the product is safe and effective if given in the proper dosage, it takes one just slip when administering a paste dewormer, and you've potentially harmed your mini.
Signs of Worms
If your miniature horse carries a heavy worm load, you can see the effects on his body even if you don't find worms in his manure. Minis with worms may have a potbelly, but their ribs show. Their hair coat appears rough, and they generally don't look good. After testing the fecal sample, your vet will likely recommend a rotational paste deworming schedule every six to eight weeks, consisting of ivermectin, pyrantel, praziquantel or others, depending on the amount of worms your mini harbors.