Performance, digestibility, nitrogen balance and ingestive behaviour of goat kids fed diets supplemented with condensed tannins from Acacia mearnsii extract

Context. Tannins are phenolic compounds derived from secondary plant metabolism that at moderate levels can limit the excessive degradation of the protein in the rumen and provide greater amino acids availability in the small intestine. Aims. Two experiments were performed to determine the best level of inclusion of condensed tannins (CT) from Acacia mearnsii extract in the diet of goat kids. An experiment was performed with 32 castrated crossbreed Boer goat kids, with a mean age of 4 months and mean bodyweight (BW) of 19.7 +/- 2.05 kg, to measure nutrient intake and performance, and another experiment was developed with 20 Boer goat kids, at 5 months of age and 29.0 +/- 2.45 kg BW, in which the digestibility, nitrogen (N) balance, microbial protein synthesis, ingestive behaviour and blood urea N were determined. In both experiments, a completely randomised design was used, including CT levels at 0, 16, 32 and 48 g/kg DM. Results. DM; crude protein; ether extract; neutral detergent fibre (NDF); non-fibrous carbohydrates and total digestible nutrients intakes, ether extract digestibility; time spent on ruminating, idling or chewing; number of chews per bolus; eating and ruminating rate of DM and NDF; N intake and retained, blood urea N and loin eye area were not affected (P > 0.05) by the addition of CT from A. mearnsii extract in the goat kid diets. However, the NDF g/kg BW and BW0.75 intakes and N faecal excretion showed a linear increase (P < 0.05). There was a linear increase trend (P < 0.1) in time spent eating, and a linear decrease on N urinary excretion by CT from A. mearnsii extract inclusion. The digestibility of DM, crude protein, NDF, non-fibrous carbohydrates and total digestible nutrients exhibited a linear decrease (P < 0.05) by CT from A. mearnsii extract inclusion. There was a quadratic increase (P < 0.05) in synthesis and microbial efficiency, final BW, average daily gain, total gain, gain:feed ratio, and hot and cold carcass weights and yields. Conclusion. The inclusion of CT from A. mearnsii extract up to 17.7 g/kg DM is recommended, as it improves the synthesis and efficiency of microbial production, increasing the gain:feed ratio and performance of goat kids.