optimizing alfalfa silage with rumen-focused tannin dynamics: toward enhanced protein retention

The effects of tannic acid (ta) and purified tannins from pistachio by-products (pb) and pomegranate pulp (pp) on the chemical composition, in vitro gas production and in situ ruminal disappearance of crude protein (cp) and tannins in alfalfa silage (as) were investigated. the experimental treatments (on a dry matter [dm] basis) included: 1) control silage (cs), 2) alfalfa silage treated with 2% ta (tas), 3) alfalfa silage treated with 2% pb tannin (pbs), and 4) alfalfa silage treated with 2% pp tannin (pps). four replicates of each treatment were prepared and ensiled for 60 days. the results showed that the treatment of as with pb and pp tannins significantly lowered the ph of silage compared to the control (p<0.05). in addition, all tannin sources significantly decreased the ammonia nitrogen (nh₃-n) content in the silages (p<0.05). the treatment of as with all sources of tannins decreased the a fraction of cp (non-protein nitrogen compounds; npn), while it increased the b1 fraction (true soluble protein). potential gas production (ml) was significantly lower in pb- and pp-treated silages compared to control and ta-treated silages (p<0.05); however, the rate constant of gas production was only reduced in ta-treated silage compared to control (p<0.05). organic matter digestibility and metabolizable energy were also significantly reduced by all tannin sources (p<0.05). compared to the control, the in situ degradability of the rapidly soluble fraction (a) of cp decreased in the as treated with pb and pp tannins, while the slowly degradable fraction (b) increased (p<0.05). the degradability rate was higher in the pbs than in the ta-treated and control silages (p<0.05). no significant differences were found among treatments in ruminal tannin disappearance, with approximately 73% of tannins disappearing at the time zero in all silages. in conclusion, incorporation of 2% tannins from pb or pp into as, compared to ta and the control, effectively reduced nh₃-n and the soluble protein fraction in the rumen without significantly altering the potential and effective degradability of protein.