Chestnut tannin supplementation at ensiling: Effects on composition, degradability, and fermentation of forage silages

Tannins are plant secondary compounds capable of forming pH-dependent reversible bonds with proteins, thereby reducing protein degradation in the silo and rumen. This study evaluated the effect of adding chestnut hydrolysable tannin (HYT) at ensiling on the chemical composition, protein degradability, and rumen fermentation of grass, whole-crop pea, and bean silages. Forages were harvested, wilted (48 h), chopped (5 cm), and ensiled in mini silos (~25 kg) with one of four treatments: 40 g kg-1 FW HYT (HT), 20 g kg-1 HYT (LT), an inoculant (IN), or water (W, control). Tannin addition reduced (p< 0.01) ammonia-N during ensiling by 31% (HT), 19% (LT), and 7% (IN) compared to W. Tannin treatments decreased (p< 0.01) CNCPS fraction A and increased (p< 0.01) fractions B1, B2, and C, as well as undegradable protein at a 0.05 h⁻¹ outflow rate (HT = 282; LT = 273; IN = 222; W = 216 g kg⁻¹ CP). In-situ degradation showed reductions (p< 0.01) in both the immediately soluble fraction “a” and total degradable fraction “a+b” with tannin inclusion. Gas production was also reduced (p< 0.01) with HT (254 ml) and LT (281 ml) compared to IN (310 ml) and W (337 ml). Furthermore, dry matter (DM) and organic matter (OM) disappearance declined (p< 0.01) with tannin treatment (DM: HT = 532, LT = 583; OM: HT = 588, LT = 605 g kg⁻¹ DM) relative to control (DM = 641; OM = 661 g kg⁻¹ DM). In conclusion, ensiling with chestnut tannins improved protein preservation and reduced the rumen degradation and fermentability of protein, suggesting potential benefits for enhancing forage utilization in ruminant diets.