Deworming Strategies and Hurricane Recovery

The level of equine parasite transmission should be diminished on pastures that were so flooded they had to be evacuated, said Craig Reinemeyer, DVM, PhD, president of East Tennessee Clinical Research in Knoxville, Tenn. "Many larvae would get washed away, and others would go down into the soil," he said. "In either case, climatic conditions right now along the Gulf Coast aren't favorable for long-term survival of infective stages (the hotter it is, the quicker they die). So, horses going back to their original pastures may theoretically face less challenge than usual. Of course, there won't be much forage to eat either, so their nutritional challenges will be more significant than the worms."

Regrettably, Reinemeyer added, the infective stages on pasture aren't going to drown.

He noted that heavy precipitation is known to break down manure piles and distribute infective larvae onto wider areas of pasture for eventual ingestion by grazing horses. "Of course, that takes place several times a year under normal climatic conditions, and only requires about 2 cm of water, not nine feet," he stated. This would mean owners or caretakers would need to make sure horses are dewormed on schedule.

He also said because of the flooding there might be a small chance for other strains of parasites to be brought onto your property. "It's possible that some parasites that were not native to your farm may come floating in from down the road," said Reinemeyer. "These differences could be qualitative (i.e., different species; for instance, Strongylus vulgaris coming back if you'd previously eradicated it on your pastures) or quantitative (e.g., resistant strains of some worms might be brought in with the floodwaters, which would mean dewormers that previously were effective on your farm might not be in the future)."

One other possibility might be sizeable outbreaks of stable flies because the females lay their eggs in dank, rotting organic material, he said. "Although face flies have been bad this year, they don't do very well in a subtropical climate," said Reinemeyer. "But, stable flies could be a real curse. Thankfully, we're a little late in the season for a huge blowout."

Reinemeyer recommended the following treatment strategy for mature horses being returned to previously flooded pastures:

"This circumstance represents a unique opportunity to ‘start over’ with a pasture, so you want to use dewormers that are known to be effective in your herd. If you don’t have specific information (as a result of Fecal Egg Count Reduction Testing) for your farm, ivermectin and moxidectin consistently demonstrate very high efficacy against strongyles. Plus, both drugs are larvicidal, meaning they can kill the migrating stages of large strongyles that are not susceptible to most other dewormers.

"Reintroducing horses also represents an opportunity to eliminate tapeworms from the premises," Reinemeyer continued. "Owners could achieve both objectives by treating with a combination product that includes praziquantel plus ivermectin or moxidectin (ComboCare, EquiMax, Quest Plus, or Zimecterin Gold). No dewormer can eradicate the small strongyles within a horse, however, so an effective control program should be followed at an appropriate interval following reintroduction. (See

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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