Changes in For­age and Di­ges­tive Prob­lems

Dressage Today - - Content - By Tanja M. Hess MV (DVM), MS, PhD Tanja M. Hess, MV (DVM), MS, PhD, is an as­so­ci­ate pro­fes­sor at The Col­lege of Agri­cul­tural Sciences, Equine Sci­ence, at Colorado State Univer­sity. She re­ceived her de­gree in vet­eri­nary medicine at Fed­eral Flu­mi­nense Uni

Chang­ing your horse’s diet can af­fect him in many ways and di­ar­rhea can some­times be a con­cern­ing side ef­fect. Only a few stud­ies have been done in the area of di­etary causes of di­ar­rhea in adult horses, as most stud­ies fo­cus on in­fec­tious agents. How­ever, many dif­fer­ent di­etary fac­tors can in­duce di­ar­rhea in horses.

Cer­tain plants, such as corns, blue-green al­gae, cas­tor beans and heather, are known to po­ten­tially cause di­ar­rhea in horses if present in the hay. Other plants that may cause di­ar­rhea are leafy spurge, wild iris, horse­tail, bit­ter weeds and mus­tard plants. Usu­ally, hay pro­duc­ers will be care­ful not to bale weeds or con­tam­i­nants into the hay. The owner should look at the bales and ex­am­ine them for any weeds, molds or dis­col­oration. Other di­etary changes, be­yond changes in hay, such as in­creased grain feed­ing or change to pas­ture, have been associated with di­ar­rhea, but no stud­ies in the area are avail­able.

When horses are on any type of diet, changes in di­etary com­po­si­tion should be done grad­u­ally. Sud­den changes in for­age type, such as de­creases in pas­ture to in­creases in hay, or de­creases in hay to in­creases in pas­ture, should be done pro­gres­sively over the pe­riod of a week. The rea­son is that the hindgut flora needs to adapt to the com­po­si­tion of the feed. In a study on risk fac­tors for colic, the in­ci­dence of colic dou­bled when the hay type and/or sup­plier was changed over the year, demon­strat­ing how changes in for­age can lead to im­bal­ances in the gas­troin­testi­nal flora. When grains were changed, risk for colic in­creased three-fold. When the diet com­po­si­tion is changed, there can be sup­pres­sion or in­crease in mi­cro­bial fer­men­ta­tion that can in­duce di­ar­rhea. A change in the mi­cro­bial flora and prod­ucts of fer­men­ta­tion can fa­cil­i­tate the col­o­niza­tion with path­o­genic bac­te­ria, lead­ing to di­ar­rhea. De­creases in hindgut pH caused by changes in diet can re­duce the re­sorp­tion of water from the hindgut, caus­ing di­ar­rhea. This oc­curs when di­ets are in­creased in starch in grain or sol­u­ble car­bo­hy­drates (fruc­tans or sug­ars in pas­ture). This is called os­motic di­ar­rhea.

When chang­ing for­age di­ets, anal­y­sis of sol­u­ble car­bo­hy­drates could help in de­ter­min­ing the risk of po­ten­tial prob­lems. Sev­eral nu­tri­tional labs can per­form this anal­y­sis. Ex­ces­sive amounts of rapidly fer­mentable or sol­u­ble car­bo­hy­drates are not prop­erly di­gested in the small in­tes­tine and flow to the hindgut, where they are quickly fer­mented.

Di­ar­rhea can be dan­ger­ous for the horse when caused by for­age change if path­o­genic bac­te­ria mul­ti­ply due to dys­bio­sis (death of nor­mal bac­te­ria and mul­ti­pli­ca­tion of lac­tic-acid-pro­duc­ing bac­te­ria) or the horse gets lamini­tis. The best mea­sure is to change di­ets slowly, over a week. When re­mov­ing horses from pas­ture, plan ahead— in­tro­duce hay over a pe­riod of sev­eral days, in­creas­ing amounts pro­gres­sively.

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