Text: Hannah Botha
Horse owners today are becoming increasingly aware of drug resistance to the common dewormers available to us, which has led many to search for alternatives. Diatomaceous earth (DE) has become one such alternative that many owners are turning to instead of the marketed dewormers.
Diatomaceous earth
DE is a source of silica which comes from the exoskeletons of dead marine microorganisms. Silica itself has many uses, including as an anti-caking agent and a way of clarifying drinks and has been shown to have some benefits for bone growth and development.
Can DE kill worms?
DE has also been shown to be successful in repelling and killing various insects and snails. Silica is a component of sand and glass, so as you might expect, DE has microscopic sharp edges. These edges cause cuts in the shells of the insect’s body, causing dehydration. In snails, DE would cut the soft, moist parts of the bodies causing dehydration and death. In addition, in insects, DE can block the holes they use for breathing, effectively suffocating them. This has led to the hypothesis that, if fed to horses, DE would cut intestinal parasites and cause their death.
Unfortunately, current studies in horses do not show any such effect. DE certainly has sharp edges, but ingesta within the horse’s gut dilute and conceal these sharp edges to such an extent that it is doubtful that the DE would come into contact with the worms, let alone ‘cut’ them. Worms and larvae can also be so small (which is why we must look under a microscope to see them) that even without the ingesta present, the DE is unlikely to impact them in the huge digestive system of the equine. Finally, intestinal parasites have thick acid-proof skin to protect them from digestive enzymes and stomach acid, making DE unlikely to affect them in the same way as more fragile insects anyway.
If we think of it from another angle, it is positive that DE does not work in this way in the intestine, as should the DE particles be sharp enough to cause damage at such microscopic level, it would be expected that they would also cause lesions in the mucosal membranes of the horse.
Can DE disrupt larvae in manure?
Another argument posed by those using DE as a dewormer is that it might disrupt developing parasitic larvae if mixed with faecal piles in the paddock. However, controlled studies have again found no effect of DE on the larvae levels in manure piles.
Can DE avoid the development of resistance?
As DE is considered ‘natural’ many people believe that worms would not develop resistance to it, as they do to the common drugs. However, resistance can develop to any type of treatment, no matter its mode of action. For example, if we were to assume that DE was effectively cutting parasites (for which there is currently no evidence), parasites with different ways of moving or with more robust exoskeletons would have an advantage and would survive treatment. These surviving parasites would then pass on these traits, and once again, we would have a resistant population.
It is worth remembering that there will always be resistance; it’s just about how quickly it develops. Dewormers are used sporadically (as and when needed), whereas DE is often used every day. This could risk overexposure to DE and speed up the establishment of resistance. If you do choose to use DE, despite the lack of evidence, please utilise it for a ‘treatment’ period at a recommended dosage rather than in small amounts every day.
It is important to note that the only thing parasites cannot develop resistance to is pasture management. Picking up manure, composting manure to kill parasite eggs and larvae, rotational grazing and grazing of multiple species on the same paddocks have all been shown to ensure low worm burdens as these work to constantly remove the source of infection.
Treating worms
Currently, the most effective way of minimising worm burdens is to use the check and treat system. This involves assessing each individual horse via faecal egg counts to pinpoint which horses ‘contaminate’ the surroundings by shedding the most eggs. Faecal egg counts identify high egg and larvae shedders, which expose the rest of the herd to more eggs and larvae. 15-20% of adult horses shed about 80% of the eggs in the paddocks, and so treating these high-shedding individuals allows us to reduce the exposure for the rest of our horses. Faecal egg counts are also very useful for checking the effectiveness of dewormers and it is highly recommended that egg counts be taken before and after treatment to ensure the treatment chosen is effective.
Conclusion
Ongoing research continues into using alternative dewormers, and more information is needed on the use of DE and its effectiveness. At present, the evidence does not support its use, and we must caution against using it as a dewormer for your horse. However, if you do choose to use DE, it is vital to make sure that you use a food-grade source and that you perform regular faecal egg counts to make sure your horse does not develop a high worm-burden that damages his intestinal system or infects the intestinal systems of other horses.