Fecal microbiota of weaned equine and mule foals grazing bermudagrass pastures

Weaning is a critical period in the lives of foals. After weaning, forage consumption represents a major challenge for both equine or mule foals.

This study evaluated the fecal bacterial concentration, composition, diversity and differential abundance in weaned equine and mule foals under rotational grazing on Bermudagrass (Cynodon spp.) pasture.

A randomized design was used with equine and mule foals grazing two rotations on three Bermudagrass cultivars (Coastcross, Florakirk, and Tifton-85). Pasture rotation occurred every 20 days. The first rotation was evaluated at 20, 40 and 60 days post-weaning, and the second rotation at 80, 100 and 120 days post-weaning. Eight weaned foals (four equine and four mules) grazed on 3 ha of each cultivar. Fecal samples were collected at the end of each grazing cycle. Bacterial populations were evaluated using culture-based methods and 16S rRNA sequencing. Forage chemical composition, bacterial counts, fecal pH, alpha diversity, and bacterial communities were analyzed using the Kruskal-Wallis's test followed by Dunn's test. Multivariate analyses of Operational Taxonomic Units (OTUs) were performed using PERMANOVA, and differentially abundant OTUs were identified using the LEfSe method.

Equine foals showed higher counts of Lactobacillus and anaerobic bacteria based on culture methods. Sequencing revealed increased relative abundance of lactic acid bacteria, Limosilactobacillus, Ligilactobacillus, Streptococcus and Enterococcus in equine foals. Mules exhibited higher fecal pH and Shannon diversity, with greater abundance of Agathobacter, Ruminococcus, Phascolarctobacterium and Treponema.

The results suggest that mule foals may are more resilient to changes in pasture and exhibit adaptive mechanisms related to digestive efficiency and forage utilization in Cynodon pastures.