Forage chemical composition drives early metabolic shifts in ponies fed different haylages

Abstract Background Rapid changes between feeds can cause dysbiosis and colic in horses. The metabolic consequences of transitioning between haylages (HY) are currently unknown. Objectives To characterise urinary and faecal metabonomics in ponies transitioned between HY varying in botanical composition and physiological age and to evaluate the speed of metabolic adaptation. Study Design In vivo experiments repeated Latin Square. Methods Eight Welsh Mountain ponies were fed four HY (R1, R2, M1, M2) across 4 × 15‐day periods; a structured 3‐day (Days 13–15) changeover was observed: old:new 70:30, 50:50and 30:70. Day 1 was 100% new haylage. Apparent digestibility was determined (multivariate mixed‐effects model) from total faecal collections on Days 10–12. Urinary and faecal collections were performed on Days 0, 5, 12 and 14. Metabolic profiling of urine and faeces was performed using NMR spectroscopy with principal component analysis and orthogonal projections to latent‐structures‐discriminate analysis to identify metabolic shifts. Alignment and normalisation (total quotient method) were carried out in Mathworks Matlab R2014a. Significance: p ≤ 0.05. Results Ponies achieved metabolic adaptation within 5 days. Metabolites were functionally stable at mid‐changeover (Day 14). Forage chemical composition drove changes. Most significant differences were between physiologically young ryegrass haylage (R1) and the other three HY, for example, D5 urinary glycine R1 992 ± 504.4 vs. R2 222 ± 130. Faecal differences included altered faecal short‐chain fatty acid plus amino‐acid metabolites, for example, from Day 12 full adaptation to 5 days post‐change for acetate: R114 ± 5.5, R2 19 ± 5.0; m ‐hydroxyphenol‐acetate: R1 0.9 ± 0.22, M2 1.2 ± 0.63; indole‐3‐acetate: R1 1 ± 0.3, M2 2 ± 1.2. Main Limitations Ponies were only fed forage. Results may not reflect more abrupt changes between HY or between different forages. Conclusions Metabolic adaptation to new HY occurred within the first 5 days and was shaped by forage composition. Three‐day structured introduction supported metabolic stability. Metabonomics provides a sensitive, non‐invasive tool and helps discriminate between forages for nutrient availability and hindgut function. Vigilance is still recommended in the first 5 days of introducing a new haylage.