Effect of Different Tannin Sources on Nutrient Intake, Digestibility, Performance, Nitrogen Utilization, and Blood Parameters in Dairy Cows

SIMPLE SUMMARY: Improving dietary nitrogen utilization efficiency or at least changing the nitrogen excretion route in lactating dairy cows, benefits both the environment and dairy economics; and reduces competition for nitrogen resources between animal feeding and human consumption. However, the effects of tannin supplements from different sources on nitrogen use in dairy cows require further investigation. This study showed that dietary supplementation with tannins in lactating dairy cows significantly decreased the milk and blood urea nitrogen concentrations, and altered the nitrogen excretion routes from the urine to the feces, which may alleviate concerns about nitrogen excretion from dairy farms to the environment. ABSTRACT: This study investigated the effect of tannin sources on nutrient intake, digestibility, performance, nitrogen utilization, and blood parameters in lactating dairy cows. Four multiparous lactating Holstein cows were used in a balanced 4 × 4 Latin square design, with each period lasting 28 days. Cows were randomly assigned to one of four dietary treatments: Control diet (CON, a totally mixed ration without tannin supplements), control diet supplemented with 3% bayberry condensed tannins (BCT), control diet supplemented with 3% Acacia mangium condensed tannins (ACT), and control diet supplemented with 3% valonia hydrolyzed tannins (VHT). Dietary treatments did not significantly affect nutrient intake, milk yield or composition, microbial protein synthesis, nitrogen utilization efficiency, or plasma concentrations of glucose, non-esterified fatty acids, β-hydroxybutyrate, total protein, and globulin, or the albumin-to-globulin ratio. Tannin supplements decreased the apparent total tract nutrient digestibility to varying degrees and significantly decreased the milk and blood urea nitrogen contents (p < 0.05). Tannin supplements altered nitrogen excretion routes in lactating dairy cows, and BCT significantly decreased the urinary nitrogen excretion (p = 0.04). Compared with the CON, ACT, and VHT diets, BCT yielded the highest nitrogen retention and nitrogen retention-to-digestible nitrogen ratio despite having a similar nitrogen utilization efficiency (p < 0.05). Bayberry condensed tannin supplementation may be a potential way to improve nitrogen utilization and reduce concerns regarding nitrogen excretion in dairy cows.