Effects of quebracho tannin extract (Schinopsis balansae) and activated charcoal on feed intake and digestibility by goats and their faecal microbial biomass

Faecal microorganisms directly influence autochthonous soil microbial biomass, microbial residues and subsequent soil C and N cycling. This study investigated the effects of feeding activated charcoal (AC) and quebracho tannin extract (QTE) on feed and nutrient intake, apparent nutrient digestibility and faecal excretion of C, N and fibre fractions in growing male goats, and on faecal microbial biomass. The completely randomised feeding trial comprised of three subsequent periods with 12 male Boer goats (age 4.8 +/- 0.59months, weight 28 +/- 3.9kg) assigned to five treatments and a control. Experimental diets contained 2 and 4% QTE (QTE2, QTE4), 1.5 and 3.0% AC (AC1.5, AC3.0) and a mixture of 2% QTE plus 1.5% AC (QTEAC). Faecal microbial biomass was measured using ergosterol and amino sugars as indices for fungi and bacteria. There were no significant effects of QTE and AC on intake of feed and nutrients. Faecal concentration of slowly decomposable carbohydrates increased with QTE as well as with AC feeding (p<0.001), whereas faecal N concentration only increased with QTE feeding (p<0.001). Although total microbial C concentration in faeces was not affected by QTE and AC feeding, QTE shifted the microbial community towards fungi (p<0.01). The results demonstrate that including up to 4% QTE in goat diets enhances the concentration of slowly decomposable N and C fractions in the faeces, whereas feeding up to 3% AC increases the faecal concentration of slowly decomposable C fractions and the faecal C/N ratio.