Seasonal Variation in the Faecal Microbiota of Mature Adult Horses Maintained on Pasture in New Zealand.
Authors: Fernandes Karlette A, Gee Erica K, Rogers Chris W, Kittelmann Sandra, Biggs Patrick J, Bermingham Emma N, Bolwell Charlotte F, Thomas David G
Journal: Animals : an open access journal from MDPI
Summary
Researchers tracked the faecal microbiota of ten pasture-kept horses over 12 months in New Zealand, using faecal sampling and next-generation sequencing to examine whether bacterial diversity changed seasonally and in response to dietary shifts when hay supplementation began (June–October). Bacterial diversity was significantly higher during months of exclusive pasture feeding, with both Simpson's and Shannon-Wiener diversity indices dropping substantially when hay was introduced—a finding that reflects the microbiota's sensitivity to changes in forage nutrient composition, particularly dry matter, protein, and structural carbohydrates. The research identified distinct bacterial community clusters corresponding to specific periods: late autumn through winter (May–July) and drought conditions (January–March), demonstrating strong associations between particular bacterial taxa and both nutritional and climatic variables such as rainfall and temperature. For equine professionals, these results underscore the importance of gradual dietary transitions and contextualised grazing management strategies, particularly for horses with compromised hindgut stability; abrupt changes between pasture and supplemented diets—or poor-quality forage during nutrient-deficient seasons—may destabilise the microbiota more severely than previously appreciated. The findings suggest that conserved forage quality and timing of supplementation should be tailored not only to climate but also to the known seasonal nutritional gaps and their microbiotal consequences in your specific geographical region.
Read the full abstract on PubMed
Practical Takeaways
- •Pasture-fed horses experience significant shifts in hindgut bacterial communities between seasons and when hay is introduced; monitor for digestive issues during dietary transitions, particularly in winter and drought periods
- •Grazing management and conserved forage preparation should account for seasonal microbial shifts—horses susceptible to hindgut disturbances may require gradual dietary transitions or targeted supplementation during nutrient-poor periods
- •Understanding that bacterial diversity is highest on fresh pasture alone suggests limiting hay supplementation when possible, and when supplementation is necessary, implementing it gradually to prevent microbiota dysbiosis
Key Findings
- •Alpha diversity of bacterial genera was significantly higher during months when horses were kept exclusively on pasture compared to months with hay supplementation (Simpson's p < 0.001, Shannon-Wiener p < 0.001)
- •Diet, season, and month had significant effects on beta diversity of bacterial genera (ANOSIM p < 0.01 for each comparison)
- •Hierarchical clustering revealed separate clades for May-July (late autumn to winter) and January-March (drought period), showing strong associations between bacterial taxa and pasture nutrient composition
- •Faecal microbiota composition reflects changes in nutrient composition of pasture driven by climatic conditions including rainfall and temperature