Complete Extruded Diet: How Does Equine Fecal Microbiota Change During Intake Adaptation?

This study aimed to investigate the gradual adaptation of the fecal bacterial community and in vitro fermentative capacity of horses fed a complete extruded diet (CED). Twelve geldings weighing 370 kg were removed from a native pasture and fed coastcross hay (Cynodon spp) for 7 days. In the second week, horses were assigned to two groups: one group was fed exclusively with coastcross hay (HAY) for 28 days and the other group fed with weekly increases of CED (30%, 60%, and 100%) to replace HAY. Fecal samples were collected on Days 7, 14, 21, and 28 for microbiota and in vitro fermentation analyses. CED intake reduces the relative abundance of phyla Fibrobacteres, Proteobacteria, Campilobacterota, Lentisphaerae, and SR1, while increasing Verrucomicrobia and Synergistetes. The fecal bacterial diversity was maintained until Day 21 (60% CED) but declined when hay was completely withdrawn. Equine fecal microbiota is diet-dependent; the stability of microbial diversity is more closely linked to the presence of roughage than to CED intake. Also, the inclusion of CED affects its microbial abundance and the detection of bacterial groups able to alter in vitro fermentative activity.