Effect Of Chronic Administration Of The Oral Antibiotic Sulfamethoxazole And Trimethoprim (SMZ) On Digestibility In Mature Horses
Pagan, J.D. and S.G. Jackson. 1993. Effect of chronic administration of the oral antibiotic sulfamethoxazole and trimethoprim (SMZ) on digestibility in mature horses. In: Proc. 13th Equine Nutr. and Physiol. Soc. Symp. Gainesville, Florida. pp. 34-36.
Horses evolved as nonruminant herbivores, entirely dependent on plant material as a source of nutrients. Through millions of years of evolution they have developed voluminous digestive tracts which house billions of bacteria and protozoa that allow the horse to breakdown and utilize plant fiber. These bacteria are essential for proper digestive function, and any disturbances to the gut microflora can lead to a wide variety of problems including colic and laminitis. One typical way in which gut microflora are imbalanced is through the chronic administration of antibiotics to the horse. These drugs are intended to fight infection by killing bacteria that have entered the horse’s
bloodstream. Unfortunately, they also kill beneficial bacteria in the digestive tract. An oral antibiotic often used in horses is Sulfamethoxazole and trimethoprim (SMZ). Sulfamethoxazole works as an antibiotic by inhibiting bacterial synthesis of dihydrolic acid by competing with para-aminobenzoic acid (PABA). Trimethoprim blocks the production of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting the required enzyme, dihydrofolate reductase. It is not known what effect chronic SMZ administration has on gut function in horses, but it has been reported to cause diarrhea and colic in humans. Therefore, this experiment was designed to test whether chronic SMZ administration affects digestibility in mature horses.