Supplementation of low dosages of condensed tannins to dairy cows

Abstract

This study evaluated the effect of low dosages (0, 0.14, 0.29, or 0.43 % of DM) of condensed tannins (TA) from Acacia mearnsii (Tanac, Brazil) on milking performance, DMI, digestibility, rumen fermentation, and N balance of dairy cows. Twenty Holstein cows (590 kg, 78 DIM) were individually fed each of 4 treatments in 5, 4 × 4 Latin squares, with 21-d periods, and 15-d adaptations. TA replaced citrus pulp in the TMR and other feed ingredients were kept constant. Diets had 17.1% CP, mostly from soybean meal and alfalfa haylage. The model had the effects of cow, period, and treatment. Linear, quadratic, and cubic contrasts of TA level were evaluated. TA had no effect (P ≥ 0.14) on DMI (21.8 kg/d), milk yield (33.1 kg/d), and components. The proportion of Mixed origin milk fatty acids (FA) was linearly increased, De Novo FA was reduced (P < 0.01), and the secretion of unsaturated FA was increased (P = 0.02) by TA. Ruminal butyrate was linearly increased (P = 0.02) and propionate was reduced (P = 0.03) by TA, while acetate did not differ (P ≥ 0.23). The A/P ratio tended (P = 0.09) to be linearly increased by TA (2.44 to 2.63). The total-tract digestibility of OM, NDF, starch, and CP did not differ (P ≥ 0.25). TA linearly reduced (P ≤ 0.03) rumen microbial yield, estimated by the concentrations of allantoin and creatinine in urine. There was no major effect of TA on eating behavior, except for a linear increase (P = 0.04) in length of the first daily meal (58.5 to 65.5 min) and on 0.45% TA cows refused feed particles > 19mm in the morning (P < 0.01 for cubic). There were trends (P ≤ 0.10) for linear decreases in MUN (16.1 to 17.3 mg/dL), urine-N (150 to 166 g/d and 29.8 to 32.9% of N intake), and PUN at 6, 18, and 21 h post-feeding and PUN 12h post-feeding was reduced (P = 0.01) by TA. The proportion of N intake in milk (27.1%) and feces (25.2%) did not differ (P ≥ 0.23). Reductions in urine-N, MUN, and PUN suggest that TA reduced ruminal AA deamination, but the decrease in rumen microbial yield may have offset the gain in dietary MP supply, and lactation performance did not differ. Overall, TA up to 0.43% of DM did not affect DMI and lactation and tended to reduce urinary N excretion.