Effect of different doses of quebracho tannins extract on rumen fermentation in ewes

Sixteen Merino ewes, fitted with ruminal cannulae, were divided into four groups of four, with the aim of studying effects of different doses of quebracho tannins on rumen fermentation in sheep. Zero (control, Q0), 0.5 (Q1), 1.5 (Q2) and 3.0 g (Q3) of quebracho tannins extract (containing 76% condensed tannins (CTs)) per kg LW per day (equivalent to 0, 28, 83 and 166 g/kg DM (dry matter) feed, respectively) were intra-ruminally administered, for up to 21 days. The rumen in sacco technique was used to examine in situ DM, crude protein (CP), neutral-detergent fibre (NDF) and acid-detergent fibre (ADF) disappearances, and a gas production method was used to examine rate and extent of in vitro gas production and in vitro dry matter disappearance (ivDMD). Alfalfa hay (AH), barley straw (BS) and Erica arborea (EA) were used in all the incubations. In vivo pH and ammonia-N and volatile fatty acid concentrations were also measured. Ewes from groups Q0, Q1 and Q2 remained healthy throughout the experiment and consumed the entire ration offered. However, ewes from group Q3 showed signs of toxicity and were removed from the trial on day 10. Data on in situ disappearances from rumen incubations conducted in those animals, on day 9, suggest that there was virtually no rumen fermentation activity. Although results obtained with the gas production and the nylon bags techniques were not exactly the same, they suggest the same general conclusions. Effect of quebracho CTs extract on ruminal fermentation activity was dependent on the dose and the substrate incubated. The daily administration of dose Q1 did not produce adverse effects on rumen fermentation. In contrast, administration of dose Q2 negatively impacted parameters such as in situ crude protein disappearance (CPD) from HA (P<0.10), in situ DM, NDF and ADF disappearances from BS (P<0.05), ivDMD from AH, BS and EA, cumulative gas production from AH fermentation (P<0.05) and AH and EA fractional rates of gas production (P<0.05). The highest dose of quebracho tannins extract (Q3) was toxic to the rumen microbial population.