The Evaluation of the Relationship Between Condensed Tannin Content and Rumen Protein Degradability in Sainfoin (Onobrychis viciifolia)

Özet

Condensed tannins (CT), naturally occurring polyphenolic compounds in some legumes such as sainfoin (Onobrychis viciifolia), can bind dietary proteins at ruminal pH levels. These tannin-protein complexes resist microbial degradation in the rumen but dissociate in the acidic environment of the abomasum, enhancing amino acid absorption in the small intestine. This study aimed to evaluate the relationship between CTs content and ruminal protein degradability in sainfoin, focusing on the potential role of CTs in protecting dietary proteins from microbial breakdown. Twenty-five sainfoin hay samples, harvested as green forage from various regions of Türkiye at 50–100% flowering stage, were used in this study. Crude protein (CP) was determined according to AOAC (2003) method 954.01, and CTs content was measured using the hydrochloric acid (HCl)-butanol assay. The effective protein degradability (EP) of the samples was assessed using the in situ nylon bag technique, following Ørskov and McDonald (1979). The ED values of samples, calculated at a ruminal outflow rate of k = 0.06 h⁻¹, ranged from 53.7% to 62.5%, indicating variation in protein degradation characteristics among the samples. Correspondingly, the condensed tannins content of the samples varied between 32.4 and 55.0 g kg-1 dry matter. Regression analysis revealed a strong negative linear relationship between CT concentration and EP, with a coefficient of determination (R²) of 0.89. This suggests that 89% of the variation in protein degradability can be attributed to differences in condensed tannin content. These findings indicate that CTs may play a significant role in reducing ruminal protein breakdown by forming stable tannin-protein complexes, thereby increasing the potential of feed proteins to reach the small intestine intact as rumen-undegraded (bypass) protein.