Influence of ruminal Quebracho tannin extract infusion on apparent nutrient digestibility, nitrogen balance, and urinary purine derivatives excretion in heifers

- Quebracho tannin infusions linearly reduce protein and carbohydrate digestibility.
- Even moderate tannin dosages decrease urinary purine derivatives excretion.
- Quebracho tannin supplementation likely not improves total duodenal protein flow.

Six fully grown heifers (491 kg body weight, standard deviation 35) fitted with ruminal cannulae received incremental dosages of a commercial Quebracho tannin extract (QTE) to investigate its effects on apparent total tract nutrient digestibilities, nitrogen balance, and purine derivatives excretion as an indicator of duodenal microbial crude protein flow. The basal diet comprised 2.6 kg/d grass hay, 2.6 kg/d concentrate feed, and 60 g/d of a mineral premix (as-fed basis) and was offered in two equal meals. The QTE was administered at 0 (CON 1), 1, 2, 4, or 6% of the daily DM intake from the basal diet (i.e., 45 g, 90 g, 180 g, and 270 g/d; as-fed basis). For this, half of the daily QTE dosage was suspended in water and intraruminally infused during each feeding. All animals simultaneously received the same QTE dosage. Every period comprised 9 d of adaptation and 6 d of total urine and feces collection. Subsequent to highest QTE dosage, infusion was ceased and after 14 d of adaptation, urine and feces were collected again for 10 d (CON 2). The QTE infusions at ≥4% lowered apparent total tract organic matter digestibility (P≤0.045). The effects were more pronounced for neutral detergent and acid detergent fiber digestibilities which decreased from 0.718 and 0.626 without QTE to 0.590 and 0.493 at 6% QTE, respectively (P<0.001). Nitrogen excretion linearly decreased in urine (P=0.003) and linearly increased in feces (P<0.001) with incremental QTE dosages. Irrespective of the dosage level, nitrogen retention was higher with than without QTE infusion (P≤0.035). Urinary purine derivatives excretion declined from 103 mmol/d at 1% QTE to 80 mmol/d at 6% QTE (P<0.001), indicating a 36% decrease in estimated duodenal microbial crude protein flow. At QTE dosages of ≥4% of DM intake, reduced carbohydrate digestibility will lower energy supply to the host animal. The pronounced decrease in estimated microbial protein synthesis even at moderate QTE levels is unlikely to be compensated by the increase in rumen-escape protein. The QTE addition to ruminant diets might not improve protein supply and performance of cattle.