Tannins of black wattle as modulators of ruminal fermentation and nutritional efficiency in grazing cattle

This study evaluated the effects of including condensed tannins from black wattle on intake, nutrient digestibility, fermentation profile, nitrogen retention, and microbial protein synthesis in cattle. Five rumen-cannulated Jersey steers (approximately 22 months old; 350 ± 50 kg BW) were used. There were no significant differences in pasture and supplement intake (P > 0.05). However, neutral detergent fiber (NDF) intake (P = 0.025), crude protein (CP) (P = 0.012), and NDF digestibility (P = 0.022) were higher in treatments with tannin inclusion. Ruminal pH was not affected (P > 0.05), while NH3-N concentration showed quadratic behavior (P = 0.018). A reduction in acetate concentrations was observed in treatments with tannin compared to the ionophore Narasin (P = 0.024), and quadratic behaviors were observed for propionate (P = 0.034), butyrate (P = 0.002), total VFA (P = 0.023), and estimated methane (P = 0.025). Nitrogen retention increased linearly with the inclusion of tannins (P = 0.026), while microbial protein synthesis showed quadratic behavior (P = 0.047), indicating a maximum point at intermediate tannin levels. The inclusion of condensed tannins from black wattle in cattle supplementation improved fiber and protein digestibility, increased nitrogen retention, and modulated the ruminal fermentation profile, reducing estimated methane production. Black wattle tannins influenced nutrient utilization and ruminal fermentation in a dose-dependent manner, without affecting intake or ruminal pH. Intermediate inclusion levels were associated with improved nitrogen utilization and reduced methane production.