Inclusion of Sainfoin in the Diet Might Alter Strongyle Infection in Naturally Infected Horses

SIMPLE SUMMARY: Control of equine parasites using synthetic drugs raises concerns, as drug resistance is increasing, especially for cyathostomins which are very common parasites in horses. As these parasites can be harmful for equine health, it is therefore necessary to find alternative solutions to control their populations. Sainfoin (Onobrychis viciifolia) is a legume that contains high levels of polyphenols, and that has demonstrated anti-parasitic activity in ruminants. This study aimed to assess whether sainfoin could also be a natural solution to regulate equine cyathostomins. We observed that the horses that consumed around 1.7 kg sainfoin per day excreted less parasites eggs in the feces, suggesting that sainfoin either decreases the number of intestinal adult worms or alters their fertility. However, we did not find any effect of the diet on egg excretion following the treatment with an anthelmintic drug. The parasite larvae that developed from eggs coming from horses fed sainfoin were less motile, which can be beneficial to reduce pasture contamination. Further studies are needed to understand the mechanisms that lead to a possible reduction in egg excretion and to provide recommendations for practitioners. ABSTRACT: It is increasingly difficult to control equine strongyles with synthetic drugs, as resistance is commonly observed. Here, we investigated the possible anthelmintic effect of sainfoin (Onobrychis viciifolia), a polyphenol-rich legume, in naturally infected horses. On Day 0 (D0), 17 horses were allocated to three different homogenous groups in terms of fecal egg count (FEC): the control group (CONT) received a diet composed on a DM basis of 83% hay and 17% wheat bran, while in the sainfoin 1 (SF1) and sainfoin 2 (SF2) groups, half or all wheat bran, respectively, was replaced by dehydrated sainfoin pellets. The infection dynamics were monitored by weekly FEC, from D0 to D84. On D28, all horses were treated with fenbendazole. Larval motility was assessed from coprocultures at D0, D28, D56 and D84. Horses in Group SF2 had lower FEC from D7 to D28. After fenbendazole treatment, no effect of the diet was measured on FEC. Both before and after anthelmintic treatment, larvae from horses consuming sainfoin were less motile than larvae from the CONT group. These results suggest that sainfoin has an in vivo anthelmintic activity in naturally infected horses, although this effect appears to be context-dependent.