Effect of sainfoin (Onobrychis viciifolia) on cyathostomin eggs excretion, larval development, larval community structure and efficacy of ivermectin treatment in horses

Abstract

Alternative strategies to chemical anthelmintics are needed for the sustainable control of equine strongylids. Bioactive forages like sainfoin (Onobrychis viciifolia) could contribute to reducing drug use, with the first hints of in vitro activity against cyathostomin free-living stages observed in the past. We analysed the effect of a sainfoin-rich diet on cyathostomin population and the efficacy of oral ivermectin treatment. Two groups of 10 naturally infected horses were enrolled in a 78-day experimental trial. Following a 1-week adaptation period, they were either fed with dehydrated sainfoin pellets (70% of their diet dry matter) or with alfalfa pellets (control group) for 21-days. No difference was found between the average fecal egg counts (FECs) of the two groups, but a significantly lower increase in larval development rate was observed for the sainfoin group, at the end of the trial. Quantification of cyathostomin species abundances with an ITS-2-based metabarcoding approach revealed that the sainfoin diet did not affect the nemabiome structure compared to the control diet. Following oral ivermectin treatment of all horses on day 21, the drug concentration was lower in horses fed with sainfoin, and cyathostomin eggs reappeared earlier in that group. Our results demonstrated that short-term consumption of a sainfoin-rich diet does not decrease cyathostomin FEC but seems to slightly reduce larval development. Consumption of dehydrated sainfoin pellets also negatively affected ivermectin pharmacokinetics, underscoring the need to monitor horse feeding regimes when assessing ivermectin efficacy in the field.

Keywords: Fecal egg count; ITS-2; nemabiome; nematode; nutraceutical; strongylid; tannin.

Graphical abstract

Fig. 1.

Experimental design. The figure depicts the time points and sampling done in this experiment.

Fig. 2.

Arithmetic average of FEC (A) and larval development rate (B) measured over the experimental period. Weekly arithmetic average FEC (A) or larval development rate (B) measured throughout the experimental period in horses receiving the control (light grey) or sainfoin (dark green) diet. The average cyathostomin FEC on day 21 (represented by the bar) was significantly different from the average FEC on day 0 (P = 0.017) (A). *Statistically significant difference in larval development rate from day 14 to day 21 between the sainfoin and control groups (P = 0.02). The bars indicate a significant difference in the mean larval development at day 7 (P = 0.04) and day 14 (P = 9.8 × 10⁻⁵), both compared to day 0 (B).

Fig. 3.

Cyathostomin larval community structure estimated using the metabarcoding approach across days and groups. Relative abundance of cyathostomin species in control (upper panels) and sainfoin-fed horses (lower panels) on days 0 and 21 of the experiment. Data are from 12 horses with samples successfully amplified.

Fig. 4.

Most abundant species estimated using the metabarcoding approach in horses from the control and sainfoin groups. Evolution of the 4 most abundant species in horses from the control and sainfoin groups between day 0 and day 21. Data are from 12 horses with samples successfully amplified.

Fig. 5.

Average fecal egg count (A) and plasma ivermectin concentration (B) measured after treatment. Average cyathostomin FEC (A) or IVM concentration in plasma (B) measured after IVM treatment is represented for horses receiving the control (light grey) or sainfoin (dark green) diet. *Statistically significant difference of FEC between the 2 groups at day 78 (P = 0.04) (A). **Statistically significant difference of average plasma IVM concentration between groups at 24 and 48 h post-treatment (P < 0.01) (B).