Fecal microbiota of weaned equine and mule foals grazing bermudagrass pastures.

Overview

• This study investigated the differences in fecal bacterial communities between weaned equine foals and mule foals grazing on Bermudagrass pastures, aiming to understand how these animals adapt microbiologically during the critical post-weaning period.

Introduction and Objective

• Weaning represents a significant transitional period for foals, during which their diet shifts from primarily milk-based to forage-based consumption.
• This dietary change poses digestive challenges, especially when foals begin grazing on Bermudagrass (Cynodon spp.), a common pasture grass.
• The research aimed to evaluate fecal bacterial concentration, composition, diversity, and differential abundance between equine (horse) foals and mule foals grazing Bermudagrass, to identify how each species’ gut microbiota adapts post-weaning.

Methods

• Study Design:
  • Randomized design involving two types of foals: four equine and four mule foals.
  • Foals grazed on three different Bermudagrass cultivars: Coastcross, Florakirk, and Tifton-85.
  • Pastures rotated every 20 days to simulate grazing management, with two rotations tracked over 120 days post-weaning.
• Data Collection:
  • Fecal samples collected at the end of each grazing cycle (days 20, 40, 60 for rotation 1; days 80, 100, 120 for rotation 2).
  • Pasture area used for grazing per cultivar was 3 hectares.
• Laboratory Analysis:
  • Bacterial concentrations evaluated by culture-based methods focusing on key bacterial populations.
  • Bacterial community composition assessed through 16S rRNA gene sequencing to identify taxa and diversity.
  • Chemical analysis of forage composition to understand dietary differences or influences.
  • Fecal pH measured as a metric indicating gut fermentation environment.
• Statistical Analysis:
  • Kruskal-Wallis’s test with Dunn’s post hoc test used to analyze differences in forage composition, bacterial counts, fecal pH, and alpha diversity.
  • PERMANOVA (Permutational Multivariate Analysis of Variance) applied to assess differences in community composition based on Operational Taxonomic Units (OTUs).
  • LEfSe (Linear Discriminant Analysis Effect Size) utilized to identify bacterial taxa differentially abundant between equine and mule foals.

Results

• Cultured Bacterial Populations:
  • Equine foals had higher counts of Lactobacillus species and anaerobic bacteria identified through culture techniques.
• Sequencing Data – Taxonomic Differences:
  • Equine foals showed increased relative abundance of lactic acid bacteria such as Limosilactobacillus, Ligilactobacillus, Streptococcus, and Enterococcus.
  • Mule foals exhibited higher abundance of fiber-degrading and fermentative bacteria including Agathobacter, Ruminococcus, Phascolarctobacterium, and Treponema.
• Diversity and Gut Environment:
  • Mule foals had statistically higher fecal pH values, indicating less acidic gut conditions compared to equine foals.
  • Shannon diversity index (a metric for microbial diversity) was significantly higher in mule foals, suggesting a more diverse gut microbiota.

Conclusions

• The gut bacterial communities of weaned equine and mule foals differ in composition, diversity, and fermentation environment when grazing on Bermudagrass pastures.
• Equine foals appear to harbor more lactic acid bacteria associated with fermentation of carbohydrates and early forage digestion.
• Mule foals demonstrate a more diverse fecal microbiota enriched with bacteria linked to fiber degradation and efficient forage utilization.
• Higher fecal pH and microbial diversity in mule foals suggest they may be better adapted or more resilient to dietary changes during pasture grazing with improved digestive efficiency.
• These findings highlight potential species-specific digestive adaptations that could influence management and nutrition strategies for weaned equine and mule foals on pasture.