A study at Texas A & M University evaluated the changes in the cecal microbiome from concentrate diets in horses [Warzecha, C.; Coverdale, J.; Janecka, J.; et al. Long-term effects of concentrate feeding on the equine cecal microbiome. Journal of Animal Science Dec 2018, vol. 96, Suppl. S3, p. 249].
One diet provided commercial concentrate at 0.6% body weight; the other diet offered the same concentrate but at 1.2% body weight. The grain component was split into two feedings 12 hours apart, along with free-choice coastal Bermuda grass hay. The seven Quarter horses in the study received no period of adaptation to these concentrate amounts. Each horse received one of the two concentrate diets for 28 days, then were allowed a washout period of 28 days before beginning the other concentrate diet for 28 days.
Cecal samples were obtained from the cannulated horses six hours after the morning feed on days 1, 7, 14, 21, and 28.
The authors conclude: “Feeding grain concentrates to unadapted horses altered the cecal microbial community, with the greatest effects observed within the initial 14 days after diet change.”