Alternatives to de-wormers ?

Biological parasitical control

Biological control is defined as the use of natural ennemies to maintain the targeted population at lower levels than those observed without the presence of the ennemies. In the case of the fight against parasite nematodes, this strategie is aimed at drastically reducing the number of infesting larvae present on pasture land. Up to now, research has been centered on nematophagous fungii, and dung beetles.

The i nterest of nematophagous fungii

Nematophagous fungii are a part of the native microfauna of the soil. They feed on free living nematode larvae species or on parasitic larvae species. Their use in a biological control program, consists in feeding a herbivore fungii spores, so that they are excreted at the same time as the developping parasites in the feces.

alternatives aux vermifuges — Nematode larvae grappling with the nematophaous fungus Arthrobotrys oligospora

Their development, which occurs silmultaneously with the development of the parasitic stages, reduces the parasitical burden of pasture land, while maintaining a residual infestation conducive to the immunity of the younger animals. The residual population of larvae, which has not been exposed to de-wormers, also contributes to diluting the parasitical population resistant to antithemintics used.

a-Larva entrapped in the filaments of Arthrobotrys oligospora.
b-Front section of a Cooperia oncophora larva surrounded by a hyphal trap from the same fungus

Trials conducted in Denmark and in tropical latitudes, in Brazil, on horses at grass, have shown a reduction in the parasitical burden on fields, and in the number of nematodes in the animals. Despite these encouraging results, there has been no commercialization undertaken so far. The main locks to be opened remain bureaucratic red tape, and associated production costs.

The role of dung beetles (Coleoptera)

Dung beetles use feces of animals to feed and to reproduce. Frequent interaction of dung beetles with feces, implies a direct contact with parasites in their free-living stages. This promiscuity directly affects the success of the parasitical cycle, either through biological or mechanical interactions : structural damage to eggs, micro climatic changes which interfere with larval development, and with larvae burying into the soil etc. It should be noted that using macrocyclic lactones, not only contributes to selecting resistant parasite populations, but also affects the population of dung beetles which could interfere with parasitic cycles.

Increasing the host’s resistance

Vaccination strategy

Immunity against roundworm, or ascarids is efficient and quick to be established, most foals, no longer being shedders as from the age of 12 months. On the other hand, anti-strongyle immunity is incomplete and takes much longer to be established regarding small strongyles. Certain studies have shown that administering larvae of Strongylus vulgaris (large strongyles), attenuated by irradiation offers a 91 % protection in subsequent infestations. Other trials however, concluded thet there was no protection. No vaccination trial against small strongyles has yet been published.

Nutrtional approach

It is commonly accepted that the nutritional status of the host influences the expression of its immunity to parasites, and that supplementing in nutrients, specifically those which have a restricting effect, can improve its resistance capacity. This has been demonstrated by certain studies carried out with ruminants. In the horse, only two studies thus far have analysed repectiveley the role of energy or nitrogenous supplementation, but they did not show a marked reduction in the number of strogyle eggs excreted by the animals.

Using the bioactive potential of plants

Another alternative worm-control strategy consists in integrating plants possessing antithelmintic properties in the ration.

Sainfoin, a potential « medicinal feed »?

Several studies carried out concerning plants or by-products of the food-processing industry containing condensed tannins, have brought to light a significant impact on trichostrongylus infections in small ruminants. Of these plants, sainfoin (Onobrychis viciifolia), has shown conducive results both in vitro and in vivo. An experiment aiming to extend these results to small strongyle control, has not yet demonstrated a decrease in the number of eggs shed by foals being given an sainfoin enriched ration (70 % of the dry matter in the ration) compared to the control group of foals.

However, scientists have observed in vitro, that sainfoin extracts restricted the development and hatching of the eggs into infecting larvae. Additional tests need to be carried out to check the effectiveness of the plant on larvae development in vivo

Other plants studied

During in vitro testing, a team of Australian scientists studied the effects of 37 plants present in Australia on the free-living stages of small strongyles. Of these plants, aqueous extracts from Acacia spp. or from Eucalyptus gomphocephala totally inhibited larval development.

To remember

For the moment, it appears difficult to offer an effective alternative solution, one that has been tried, tested and approved. Numerous research avenues are open and several promising results should lead to applications in the field in the forseeable future. The use of nematophgous fungii or bioactive plants appear to be the most convincing options to date, both in their measured effects, and in their practical implementation.