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Impact of Weight Loss on the Equine MicrobiomeBy Kentucky Equine Research Staff · October 4, 2017

Obesity continues to plague horses, negatively impacting overall health and quality of life. As such, weight management strategies for horses abound, but not all take into consideration special features of the equine gastrointestinal tract. Realizing the importance of intestinal microbiome stability in horses, one group of researchers* recently assessed the impact of a “diet” on the population of microbes in the large intestine.

“The bacteria, viruses, fungi, and other microorganisms residing in the intestinal tract of horses play a vital role in digestive health. These organisms, collectively referred to as the microbiota, help the immune system respond quickly and effectively to infection; improve gut health in patients with inflammatory bowel diseases; help prevent antibiotic-induced diarrhea; and protect against infectious agents that cause diarrhea,” summarized Kathleen Crandell, Ph.D., a nutritionist at Kentucky Equine Research (KER).

Any abrupt change in diet can induce colic or diarrhea, possibly due to changes in the composition of the intestinal microbiota. To determine the impact of a reduced diet on intestinal microbiomes, a team of researchers from the United Kingdom offered adult horses with a body condition score greater than 7.8 one of two weight-loss diets.

Both diets provided 1.25% of body mass in dry matter and an equal number of calories. The first diet offered a chaff-based complete feed (64%) and low-energy grass hay (36%), and the second diet offered a ration balancer (8%) and the same low-energy grass hay (92%). At the 10- and 16-week marks of the study, the scientists found that the two most predominant microorganisms in the fecal samples of all the horses were Firmicutes and Bacteroidetes. These findings were not unexpected and mirror the results of other studies. More interesting was that over time, the Bacteroidetes levels decreased and the Firmicutes increased; however, the two remained predominant.

The microbial community was relatively stable during the short study period, suggesting that a restricted diet had no effect on the primary inhabitants of the intestinal microbiome.

“These findings suggest that owners should not be concerned about placing their overweight horses on an appropriately designed weight-loss program as long as the diet is consistent in its content and nutritionally balanced,” Crandell concluded.

She added, “Owners wishing to help their horses lose weight but looking for some help should consult with a KER equine nutrition advisor.” Completing a short, online form can start the process today.

*Dougal, K., P.A. Harris, S.E. Girdwood, et al. 2017. Changes in the total fecal bacterial population in individual horses maintained on a restricted diet over 6 weeks. Frontiers in Microbiology. 8:1502.