Synergistic effects of Ferula asafoetida extract and condensed tannins from raisin pomace on in vitro cecal fermentation kinetics and nutrient digestibility in horses

Background and Aim: The equine hindgut depends on microbial fermentation for efficient nutrient utilization but remains vulnerable to dysbiosis, hindgut acidosis, and suboptimal fiber digestion. Growing restrictions on antibiotic and synthetic feed additives have increased interest in natural phytogenic compounds. Medicinal plant extracts and condensed tannins are promising candidates to modulate microbial activity, improve fermentation efficiency, and enhance nutrient digestibility. This study aimed to investigate the individual and combined effects of hydroalcoholic extract of Ferula asafoetida and condensed tannins extracted from raisin pomace on equine cecal fermentation parameters and nutrient utilization using in vitro gas production and batch culture techniques. Materials and Methods: A 2 × 2 factorial in vitro design was used with four treatments: control (C; basal diet only), F. asafoetida extract (A; 30 mg), condensed tannins from raisin pomace (G; 50 mg), and their combination (A × G). Fecal inoculum was collected from four healthy 14-month-old Arabian geldings adapted for 14 days to a forage-based maintenance diet. Fermentation kinetics were evaluated over 120 h using the in vitro gas production technique and fitted to the Gompertz model. Parallel batch cultures measured pH, ammonia-nitrogen (NH₃-N), and apparent disappearances of dry matter (DM), crude protein (CP), acid detergent fiber (ADF), and neutral detergent fiber (NDF). Data were analyzed using PROC GLM in SAS with Tukey–Kramer post-hoc tests (p < 0.05). Results: Cumulative gas production at 120 h was significantly higher in G (340.5 mL) and A × G (340.3 mL) than in C (228.8 mL) (p < 0.01), with faster fermentation rates and shorter lag times (p < 0.01). Terminal pH values remained stable (6.33–6.40) across treatments with no indication of acidosis. NH₃-N concentrations were elevated in G (26.0 mg/dL) and A × G (25.5 mg/dL) compared with C (24.5 mg/dL) (p < 0.01). Apparent digestibility improved markedly: DM increased from 64.5% (C) to 70.3% (G), CP from 60.3% (C) to 66.9% (G), with parallel positive trends observed for ADF and NDF (p < 0.01). Conclusion: Supplementation with F. asafoetida extract and condensed tannins from raisin pomace, especially in combination, enhanced fermentation efficiency, accelerated substrate degradation, and improved nutrient digestibility while maintaining stable pH in an in vitro equine cecal model. These findings indicate strong potential for these phytogenic compounds as sustainable natural feed additives to optimize equine hindgut function. In vivo validation, dose optimization, and long-term microbiome studies are recommended to confirm practical efficacy and safety in horses. Keywords: acidosis, cecal fermentation, condensed tannins, equine nutrition, Ferula asafoetida, horse feed additives, in vitro gas production, nutrient digestibility, raisin pomace tannins.