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“Are alterations in the gut microbiota responsible for equine Fecal Water Syndrome?”

Horse Fecal Water Syndrome

Fecal Water Syndrome (FWS) is a condition where affected equids pass droppings of normal consistency but they are accompanied by watery fecal content either before, during or afterwards1. The cause of FWS remains unknown and has no apparent link to dentition or parasite status. Affected animals typically do not overtly display symptoms beyond occasional discomfort during defecation, although loss of weight and condition, and dermatitis of stained hind limbs is also reported.

The potential role of dysbiosis in the gastrointestinal system with FWS was examined in a recent study2. Dysbiosis refers to imbalances in the microbial communities of the gut microbiome and their functionality and has previously been linked to colic3 and laminitis4. This study was conducted as a prospective, case-controlled study and aimed to examine the fecal microbial community populations between animals presenting with FWS and stable-matched controls. 31 horses were recruited and included 16 FWS ‘affected’ and 15 stable-matched controls. ‘Affected’ animals were defined as those that had presented with FWS for at least four months, had fecal water being passed on at least one day within a week , and had previously had an otherwise normal clinical examination. The stable-matched controls were of the same age, breed, sex and shared the same management environment as affected horses, but had no evidence of FWS.

Fecal samples were collected from all horses during early spring and again in autumn. Spring had been identified as when FWS frequently occurred in this study population. Some horses also had gastroscopy, fecal egg counts and examination of salivary cortisol. DNA was extracted from the fecal samples to examine the microbial population structure via metagenomic sequencing. This permitted identification of taxonomic groups in the bacterial microbiota populations and comparison between FWS animals and their matched controls.

No significant results were obtained from the fecal egg count analysis, salivary cortisol measurements or gastroscopy examinations. Analysis of microbial population composition revealed no significant differences between FWS horses and their matched controls (p > 0.3). Some members of the bacterial microbiota populations were identified as ‘enriched’ in the control and FWS horses in spring and in autumn, suggestive of health and seasonal differences, although no difference in bacterial diversity between the two study populations was observed.

Several factors are likely involved in the pathogenesis of FWS, including stress, management regimes and other individual characteristics. This study suggests only minor differences are observed in the gastrointestinal microbiota of FWS and unaffected animals, indicating that further research is needed to explore the role of the microbiome in the condition, and in the identification of therapeutic and supportive methods.

1. Kienzle, E., Zehnder, C., Pfister, K., Gerhards, H., Sauter‐Louis, C. and Harris, P. (2016). Field study on risk factors for free fecal water in pleasure horses. J Equine Vet Sci., 44, 32‐ 36. Available HERE

2. Schoster, A., Weese, J.S., Gerber, V., and Nicole Graubner, C. (2020). Dysbiosis is not present in horses with fecal water syndrome when compared to controls in spring and autumn. J Vet Intern Med., 34, 1614– 1621. Available HERE

3. Weese, J.S., Holcombe, S.J., Embertson, R.M., Kurtz, K.A., Roessner, H.A., Jalali, M. and Wismer, S.E. (2014). Changes in the faecal microbiota of mares precede the development of postpartum colic. Equine Vet J., 47, 641‐ 649. Available HERE

4. Milinovich, G.J., Trott, D.J., Burrell, P.C., Croser, E.L., Al Jassim, R.A.M., Morton, J.M., Van Eps, A.W. and Pollitt, C.C. (2007). Fluorescence in situ hybridization analysis of hindgut bacteria associated with the development of equine laminitis. Environ Microbiol., 2090‐ 2100. Available HERE

5. Parkes, G.C., Rayment, N.B., Hudspith, B.N., Petrovska, L., Lomer, M.C., Brostoff, J., Whelan, K. and Sanderson, J.D. (2012), Distinct microbial populations exist in the mucosa‐associated microbiota of sub‐groups of irritable bowel syndrome. Neurogastroenterology & Motility, 24, 31-39. Available HERE

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