The effect of feeding a mix of condensed and hydrolyzable tannins to heifers on rumen fermentation patterns, blood urea nitrogen, and amino acid profile

The objective of this pilot study was to begin to evaluate the effect of feeding a mix of condensed and hydrolyzable tannins to heifers on rumen fermentation patterns, blood urea nitrogen (BUN), and amino acid profile. Four growing Holstein-Friesian x Jersey heifers with a mean live weight of 319.5 +/- 8.38 kg and a mean body condition score of 4 +/- 0.17 out of 10 were used in a cross-over design. Heifers were either orally administered the mixed tannin treatment at 0.15% of daily DMI or a control dose of water whilst consuming perennial ryegrass baleage and soybean meal for 12 days in a cross-over trial. Administration of mixed tannins reduced non-glucogenic volatile fatty acid (VFA) production by 2%, the acetate to propionate (A:P) ratio by 13%, and the relative abundances of specific methanogenic archaea - i.e., Methanobrevibacter and Methanosarcina. The tannin treatment also reduced BUN concentration by 12% in comparison with the control dose of water, which indicates associated reductions in daily urinary nitrogen excretion and therefore environmental impact. The effects of ingestion of mixed tannins on rumen function in this study would be expected to result in a reduction of both methane and urinary nitrogen excretion and thereby reducing the environmental impact of heifers consuming conventional feeds.