Fermentation of six different forages in the semi-continuous fermentation technique Caesitec.
Authors: Vosmer J, Liesegang A, Wanner M, Zeyner A, Suter D, Hoelzle L, Wichert B
Journal: Journal of animal physiology and animal nutrition
Summary
# Fermentation dynamics of fresh forages in the equine hindgut: an in vitro investigation When horses transition abruptly from conserved forage to fresh pasture, the hindgut microbiota must adapt rapidly to different carbohydrate profiles—particularly the shift from starch-based digestion to fructan fermentation. Vosmer and colleagues employed Caesitec, an in vitro semi-continuous fermentation system, to simulate this dietary transition across six forage types (ryegrass, tall fescue, grass and legume mixtures) under controlled conditions, monitoring pH, ammonia, gas production, and microbial populations at multiple timepoints over the diet-change period. Despite grass mixtures containing substantial fructan loads (up to 3.75 g/kg), pH remained within physiological limits (6.58–6.83) across all forages, and bacterial populations—though increasing post-transition—did not shift into pathogenic patterns. These findings suggest that even significant fructan intake from spring pasture does not necessarily trigger the severe dysbiosis associated with acute hindgut acidosis, provided the transition occurs relatively gradually. For practitioners managing grazing protocols, this offers reassurance that well-managed pasture introduction carries lower risk of microbiotal disruption than previously feared, though field conditions (stocking density, forage maturity, individual variation) warrant continued cautious management during seasonal turnout.
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Practical Takeaways
- •Abrupt transitions from hay to fresh grass (even high-fructan varieties) did not produce pathological hindgut changes in this in vitro model, suggesting some tolerance to dietary shifts
- •Monitor pH and fermentation markers when changing from hay-based to forage-based feeding, as bacterial populations and gas production increase significantly
- •Different forage types (ryegrass, fescue, clover, lucerne) show varying carbohydrate profiles and fermentation characteristics that may influence hindgut health during transition periods
Key Findings
- •pH values remained in physiological range (6.58-6.83) across all forage types tested
- •Grass mixtures contained the highest fructan amounts, with maximum 3.75 g/kg in Swiss pasture
- •Gas formation, anaerobic and aerobic bacterial numbers increased following diet change from hay to forage
- •Abrupt diet change to high-fructan forages did not cause permanent pathological changes in hindgut flora