fecal egg count | Horse Racing Free Tips

Double Down: Traditional Deworming Increases Drug Resistance At Alarming Rate

Traditional deworming methods dictate that all horses on a farm be dewormed with moxidectin or ivermectin at specific intervals, usually every other month or quarterly. Though significantly easier on farm managers, this method increases anthelmintic resistance two to three times more rapidly than other deworming programs, reports The Horse.

Dr. Thomas Geruden, with Zoetis in Belgium, said these results are not surprising as the worm population is continuously pressured for selection of survivable genes in the calendar-based deworming routine.

Geurden and other researchers in Belgium, along with scientists at the Gluck Equine Research Center in Lexington, Ky., studied two farms that utilized the standard deworming protocol on their Belgian draft horses.

The deworming schedule should have corresponded with the timeline of worm egg development, but drug resistance has caused the worm eggs to appear twice as fast as expected.

Fecal egg counts on every horse on the farm were performed every two weeks from April to September for three years. Horses that had more than 250 eggs per gram of manure were given pyrantel embonate, an alternative dewormer. All other horses were treated with standard anthelmintics in the spring and fall, reducing their deworming by half or two-thirds.

The researchers used the fecal egg counts, both before and after treatment, to create a model of worm life cycles that could predict drug resistance over the next 40 years. The team found that the alternative dewormer maintained low egg counts in all horses and slowed drug resistance in worms by 200 to 300 percent.

The scientists also found that the horses considered “high shedders” of worms were almost always under 5 years old. This knowledge might allow horse owners and caretakers to target which horses may need fecal egg counts run more often – and which may need more-frequent treatments.

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The data suggests that fecal samples should be gathered for egg counts between 42 and 56 days after the spring moxidectin/ivermectin treatment, with a second sample taken between days 98 and 112. These numbers will help determine future egg counts and reduce deworming frequency.

The ability to model the rate of anthelmintic resistance using different deworming protocols has been helpful when discussing deworming with both horse owners and vets, the researchers found. A deworming plan specifically tailored to a farm may be more expensive initially, but the less-frequent, targeted deworming will pay off financially in the long run as dewormer resistance slows.

Bots: Where Fecal Egg Counts Fail

A fecal egg count test is a common horse health practice designed to combat the overuse of equine dewormers and consequent drug resistance. Though the test is helpful in determining which horses need to be treated for parasites, there is one parasite that escapes being found on the screening: bots.

Fecal egg counts don't show the bot load a horse is carrying because bot eggs are not found in horse manure. Bot flies lay eggs on a horse's body, often on the lower legs and chest. As the horse licks the eggs, they hatch and he swallows the larvae, where they enter his digestive tract. The larvae, not eggs, leave via manure and the process begins again.

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Bot fly eggs look like small yellow grains of rice that stick to horse's hair. To remove them, horse owners can use a bot knife, which has a serrated blade, or a fiberglass block, which grabs and removes the eggs.

If bot fly eggs are removed diligently throughout the year, a horse owner may be able to skip deworming for bots – the horse will be fine if he ingests a few. If the horse isn't groomed regularly, however, it's worthwhile to give him a single dose of moxidectin or ivermectin after the first frost.

Study: Flaxseed Oil Can Reduce Strongyle Load In Horses

Vegetable oils are often added to equine diets to supplement fat and energy, but adding flaxseed oil (also called linseed oil) now has an additional equine health benefit: it can significantly reduce strongyle load in horses. This finding is especially important as strongyles have become more resistant to available deworming medications.

A Polish study added pure flaxseed oil to the diet of 15 Thoroughbred and 12 Arabian horses that were fed oats, muesli, and hay three times a day. The horses were separated into four groups fed soybean oil, flaxseed oil, flaxseed oil and vitamin E, and one group with no added oil that served as a control. Lead researcher Dr. Wanda Górniak had the horses dewormed with ivermectin and praziquantel in February 2020.

In June 2020, researchers performed fecal egg counts on samples from the horses. The researchers found that 25 of the 27 horses had worms, with strongyles the most prevalent; one-third of the horses also had threadworms. The horses that had been fed flaxseed oil have the lowest prevalence of strongyles (71 percent compared to 100 percent in other groups).

The scientists concluded that the adding flaxseed oil to a horse's diet significantly reduces its strongyle worm load.

Read the study here.

Veterinarians: Dewormer Resistance Must Be Addressed To Avert Equine Welfare Disaster

Though veterinarians and equine caretakers around the world have stressed the importance of forgoing the once-standard practice of rotational deworming, a recent study shows that dewormer resistance is still looming. Currently, small redworms and large roundworms are resistant to all available dewormers; no new dewormers are currently in creation.

Members of the British Equine Veterinary Association (BEVA) anthelmintic working group wrote to the Veterinary Record to express their concern over the findings of a small-scale study. Dr. David Rendle and his colleagues state that a “anthelmintic resistance disaster” is looming unless horse owners change horse-keeping ways.

The study found that although there has been an uptick in the number of fecal worm egg counts (FWECs) performed, there has not been a corresponding downward trend in dewormer sales. The BEVA working group gathered information on the number of fecal worm egg counts completed and the sale of dewormers in the U.K. from 2015 to 2018.

Though FWECs increased by 29 percent, the doses of dewormer sold only fell by 2.9 percent over the same period. The sale of these drugs dropped 8 percent between 2015 and 2016, and then rose every year after that.

If the deworming guidelines were being followed correctly, and dewormers would only be given when a FWEC deemed them necessary. There should be at least twice as many FWECs completed as doses of dewormer sold. However, the data shows that there was only one FWEC completed for every 11 doses of dewormer sold.

The authors also point out that moxidectin sales remained high throughout the study period though experts have noted that it should not be used as a routine dewormer in horses.