Effect of quebracho chestnut tannin extracts at 2 dietary crude protein levels on performance, rumen fermentation, and nitrogen partitioning in dairy cows.
Our objective was to determine the effects of a tannin mixture extract on lactating cow performance, rumen fermentation, and N partitioning, and whether responses were affected by dietary crude protein (CP) The experiment was conducted as a split plot with 24 Holstein cows (mean standard deviation; 669+ 55kg of body weight; 87+ 36 d in milk; 8 ruminally cannulated) randomly assigned to a diet of [dry matter (DM) basis] 15.3 or 16.6% CP (whole plot) and 0, 0.45, 0.90, or 1.80% of a tannin mixture in three 4x4 Latin squares within each level of CP (sub plot) Tannin extract mixture was from quebracho and chestnut trees (2:1 ratio) Dietary CP level did not influence responses to tannin supplementation. A linear decrease in DM intake (25.5 to 23.4kg/d) was found, as well as a linear increase in milk/DM intake (1.62 to 1.75) and a trend for a linear decrease in fat and protein corrected milk (38.4 to 37.1kg/d) with increasing levels of tannin supplementation. In addition, there was a negative linear effect for milk urea N (14.0 to 12.9mg/dL) milk protein yield (1.20 to 1.15kg) and concentration (2.87 to 2.83% Furthermore, the change in milk protein concentration tended to be quadratic, and predicted maximum was 2.89% for a tannin mixture fed at 0.47% of dietary DM. Tannin supplementation reduced ruminal NH3 N (11.3 to 8.8mg/dL) total branched chain volatile fatty acid concentration (2.97 to 2.47mol/100mol) DM, organic matter, CP, and neutral detergent fiber digestibility. Dietary tannin had no effect on intake N (587+ 63g/d) milk N (175+ 32g/d) or N utilization efficiency (29.7+ 4.4% However, feeding tannin extracts linearly increased fecal N excretion (214 to 256g/d) but reduced urinary N (213 to 177g/d) and urinary urea N (141 to 116g/d) excretion. Decreasing dietary CP did not influence milk production, but increased N utilization efficiency (milk N/N intake; 0.27 to 0.33) and decreased milk urea N (15.4 to 11.8mg/dL) ruminal NH3 N (11.0 to 9.3mg/dL) apparent digestibility of DM (66.1 to 62.6% organic matter (68.2 to 64.3% and CP (62.9 to 55.9% as well as urinary N excretion (168 vs. 232g/d) Results of this study indicated beneficial effects of 0.45% tannin extract in the diet on milk protein content. Increasing tannin extract levels in the diet lowered urinary N excretion, but had detrimental effects on DM intake, milk protein content, milk protein yield, and nutrient digestibility.
Journal of dairy science