While deworming strategies can help reduce horses’ internal parasite burdens, research indicates diet might also play a role in mitigating strongyle infection. Researchers in France recently examined the potential for a dietary alternative to anthelmintic drugs in horses.
Past study results have pointed to a polyphenol-rich plant called sainfoin as a dietary means of reducing egg excretion in the feces and reducing the motility of infective larvae. Diet affects intestinal microbiota diversity, composition, and function. Research also confirms that a high-starch diet initiates intestinal dysbiosis and permeability.
Study Population
In this study, which took place from May to September 2021, researchers fed two diets to 12 horses with natural strongyle infections. The horses were last dewormed at least seven months before the start of the study. The two diets—high-fiber (hay) and high-starch (hay with barley)—were supplemented with either sainfoin (a type of legume that is a non-bloat alternative to alfalfa) or sunflower/hay pellets as a control. After 21 days of this feeding regimen, all horses were fed free-choice hay for a washout period of 21 days. Each horse received each of the four experimental protocols for 21 days followed by a 21-day washout period between trials.
Study Methodology
Researchers obtained fecal egg counts prior to the experiment and then weekly. They evaluated larval motility after 21 days. They also collected blood on Day 21 to assess hematocrit, LPS (lipopolysaccharide) concentration and other chemical values, procalcitonin, and cytokine levels. They evaluated the effects of supplementation for:
- Strongyle egg amounts excreted in feces and larval motility.
- Changes in large intestinal microbiota regarding diversity, composition, function, and activity.
- Systemic immune markers and equine health.
Hypotheses and Results
The authors hypothesized that sainfoin would reduce egg secretion and larval motility when added to the diet. They also expected the high-starch diet to result in dysbiosis with increased markers of inflammation and the sainfoin to improve inflammatory status.
The results indicate time, diet, and supplementation affect fecal egg counts. One goal of the study was to determine if sainfoin could serve as a useful anthelmintic. The authors summed up their findings:
Diet had no effect on immunological markers, neither systemic nor pro-inflammatory, possibly as a result of the short 21-day trial duration. (They assessed three markers for systemic immunity: peripheral white blood cells, procalcitonin concentration, and specific serum cytokines.) The concentration of circulating LPS and acetate serves as a proxy for intestinal mucosa integrity and permeability; the researchers found no difference between treatments. However, fecal acetate levels increased with the high-starch diet, suggestive of reduced absorptive capacity of the intestinal mucosa. Bacterial composition and diversity differed between the high-starch and high-fiber diets, with greater diversity present in the high-fiber diet and more volatile fatty acids (VFA) produced by microbiota in the high-starch diet. The authors found only “minor effects of adding sainfoin on the diversity, composition, function, and activity of the microbiota and on the immune markers considered here. These findings therefore suggest that if any, the anthelmintic effect of sainfoin is not mediated by the microbiota.”
Microbiota in horses fed the high-fiber diet had greater biodiversity than horses fed high starch. In addition, “cellulolytic bacterial functions were reduced in high-starch-fed horses while the amylolytic bacterial functions were enhanced, resulting in higher concentration of fecal VFAs.” Microbial fermentation from starch reduces pH levels and might contribute to increased egg excretions.
The number of parasite eggs excreted in feces increased rapidly in horses fed a high-starch diet for 21 days, thus increasing pasture contamination and parasite transmission. In this study, horses fed a high-starch diet excreted more parasite eggs than those on a high-fiber diet. The polyphenol-rich sainfoin pellets diminished egg secretion increases in horses on the high-starch diet, indicating diet affects egg excretion.
Larval motility did not differ between diets but was lower in horses receiving the sainfoin supplement compared to controls, indicating the supplement plays a role in “hindering transmission of parasites to other hosts.” Motility might be affected due to alterations of the third-stage larvae cuticle (the protective exoskeleton).
Final Thoughts
In conclusion, a low-starch, high-fiber diet coupled with sainfoin supplementation might mitigate infection and transmission of strongyles in horses. Implementing this study over several months instead of a short three-week period could provide further insight on sainfoin’s effectiveness, especially with regard to seasonal variations in internal parasite egg secretion and larval infectivity.
Reference
Laroche N, Grimm P, Julliand S, Sorci G. Diet modulates strongyle infection and microbiota in the large intestine of horses. PLOS ONE Apr 2024; DOI: 10.1371/journal.pone.0301920
Related Reading
- Disease Du Jour: Fecal Egg Counts for Horses
- An Update on Multi-Drug-Resistant Parasites in Horses
- Tapeworm Resistance in Horses
Stay in the know! Sign up for EquiManagement’s FREE weekly newsletters to get the latest equine research, disease alerts, and vet practice updates delivered straight to your inbox.
