Supplementation of low dosages of Acacia mearnsii tannin extract to dairy cows

Abstract

The supplementation of dairy cows with tannins can reduce the ruminal degradation of dietary protein and can have beneficial effect on urinary N excretion, but high dosages can penalize rumen function, diet digestibility, feed intake, and milk yield. This study evaluated the effect of low dosages (0, 0.14, 0.29, or 0.43% of DM) of condensed tannin extract from the bark of Acacia mearnsii (TA) on milking performance, dry matter intake (DMI), digestibility, chewing and sorting behaviors, rumen fermentation, and N partition of dairy cows. 20 Holstein cows (34.7 ± 4.8 kg/d, 590 ± 89 kg, and 78 ± 33 d in lactation) were individually fed a sequence of 4 treatments in 5, 4×4 Latin squares (21-d periods). TA replaced citrus pulp in the total mixed ration and other feed ingredients were kept constant. Diets had 17.1% crude protein, mostly from soybean meal and alfalfa haylage. The statistical model had the effects of cow, period, and treatment. Linear, quadratic, and cubic contrasts of TA level were evaluated. Significance was declared at P ≤ 0.05 and tendency at P ≤ 0.10. TA had no effect on DMI (21.8 kg/d), milk yield (33.1 kg/d), and milk components. The proportion in milk fat of Mixed origin fatty acids (FA) was linearly reduced, De Novo FA was increased, and the daily secretion of unsaturated FA was increased by TA. Cows fed TA had linear increase in the molar proportion of butyrate and reduction in propionate in rumen fluid, while acetate did not differ. There was a tendency for the A/P ratio to be linearly increased by TA. Cows fed TA had linear reduction in rumen microbial yield, estimated by the concentrations of allantoin and creatinine in urine, and total protozoa concentration did not differ. The total tract apparent digestibility of neutral detergent fiber, starch, and crude protein did not differ. There was no major effect of TA on chewing behavior, although TA induced a linear increase in meal size and length of the first daily meal and reduced meal frequency per d. Rumination behavior did not differ. Cows fed 0.43% TA refused feed particles > 19 mm in the morning. There were tendencies 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 plasma urea-N (PUN) at 6, 18, and 21 h post- morning feeding, and PUN 12 h post-feeding was reduced by TA. The proportion of N

intake in milk (27.1%) and feces (25.2%) did not differ. 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 absorbable dietary protein supply, and

lactation performance did not differ. Overall, TA up to 0.43% of DM did not affect DMI and lactation and there was a tendency to reduce urine-N excretion.