This document, prepared by the veterinary team at Clinique LIVET, aims to improve best practices for deworming in accordance with new field data and scientific advances.
Among the intestinal parasites of the horse, our 3 main enemies are :
– The small strongyles, which cause severe diarrhea in yearlings, young horses and older horses, and can cause weight loss in horses of all ages.
– The parascaris, which mainly infest foals up to one year old, and which cause growth retardation, but above all can cause fatal colic through intestinal obstruction.
– Anoplephali, commonly called tapeworms which cause colic in young horses.
Of these 3 parasites, The first two are known to have developed resistance to some of the most commonly used dewormers.. Effective molecules are few in number and have been used for many years. Numerous cases of resistance in various parasites to commonly used dewormers have been described worldwide, and particularly in France. The emergence of these resistances is linked to excessive and/or inappropriate use of dewormers.
The first objective of these changes in our deworming habits is Deworm less and deworm better This is to prevent the emergence or increase of resistance to dewormers. Therefore, it is necessary to target specific parasitic species based on the horse's age, lifestyle, and the season.
The second objective is to maintain a population of parasites susceptible to dewormers. by reducing drug pressure, as we also do with antibiotics. It is unrealistic to hope to eradicate intestinal parasites from horses. The infestation must be kept at a low enough level to avoid causing disease.. However, a large proportion of adult horses are able, thanks to their immune system, to maintain their parasitic infestation at an acceptable level for much of the year, without deworming. The use of dewormers should therefore be done judiciously, following a fecal examination. to check for the presence of specific parasites. This reduces the number of deworming treatments given annually and allows a "refuge" population of parasites to remain susceptible to deworming. We sincerely hope that more fecal egg counts will be performed to ensure appropriate deworming. Furthermore, from a budgetary standpoint, the savings made on deworming medication will more than cover the costs of fecal egg counts..
It is important to’to establish with the veterinarian who takes care of your livestock, a protocol for reasoned deworming for each age class in your breeding operation (foals, weanlings, yearlings, 2-year-olds, adults in pasture, adults in stalls, pregnant mares).
Unfortunately, The emergence of resistance to dewormers is strongly dependent on breeding and deworming practices. Therefore, resistance to different dewormers varies from one farm to another. To be as effective as possible, and to avoid using ineffective dewormers, it is recommended that each farm test the effectiveness of the treatments used with a fecal egg reduction test. This involves performing a COPROSCOPY before and after deworming to check if the parasites have been killed by the dewormer. This allows us to know the resistances already present in the herd and thus adapt the deworming program.
The horses and foals that arrive at your breeding farm after having stayed in another facility in France, or even abroad, are likely to introduce new parasites into your livestock, or even new forms of resistance.
We therefore recommend systematically performing a COPROSCOPY on all animals (especially foals) entering the stud farm. (return from abroad, new purchase, etc.), and to deworm them according to the results of the coproscopy, before putting them in the pasture, to avoid contamination of the pastures by parasites foreign to the farm.
When horses are in the pasture, they become contaminated with parasite eggs and larvae. In order to limit the degree of infection, it is important to reduce the parasite load present in the pastures, which in some cases may reduce the frequency of administration of dewormers. This can be achieved by avoiding overgrazing.e. The more horses there are in the same pasture, the higher the parasite load per square meter. Another alternative is to collect the manure in the pasture. Ideally, collecting it twice a week very effectively limits the risk of contamination.
Unfortunately, this technique is not very practical because it is very time-consuming and requires expensive equipment. Pasture rotation is a third alternative. Unfortunately, strongyle larvae can survive for a long time in the environment when climatic conditions are favorable.. An annual rotation can therefore be carried out, possibly alternating with
other species (cattle, sheep). Regarding Parascaris infection, the eggs are very resistant. A thorough cleaning of the foaling boxes is therefore recommended.
Rational deworming programs cannot be designed universally, and must be adapted according to the horse population and parasites of each farm. That's why you should discuss your deworming protocol with your veterinarian. In this way, thanks to everyone's efforts, we can participate in the combating the emergence of parasite resistance, and ensuring a better future for the horses of tomorrow !
The entire veterinary team at the clinic is available to work with you on this responsible management of parasite control. We can also, in the event of a confirmed problem or any doubt about the parasite status of your herd, conduct parasite audits to assess the issues on a farm-wide scale.
Dr Johanne VANDERSTOCK, dipl. ACVIM 
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