Abstract:
Tannins have become important phytochemicals in ruminant production, due to their
wide range of biological activities. The use of a crude extract often comes with limitations, such
as reduced feed intake and fibre digestibility, which could be overcome by the use of encapsulated
tannin extract. In this study, four rumen-cannulated Merino wethers were used in a 4 4 Latin square
design to determine the e ect of encapsulating Acacia mearnsii tannin extract on intake, nutrient
digestibility, and methane emission. The animals were placed on one of the following diets: control
diet only, diet + silvafeed (Silvafeed ByPro, 10 g/kg feed), diet + Acacia tannin extract (ATE), 40 g/kg
feed), and, diet + lipid-encapsulated-ATE (palm oil encapsulated ATE, 50 g/kg feed) in 4 cycles.
Wethers were o ered an Eragrotis and Lucerne hay-based total mixed ration diet above maintenance
requirement with forage: concentrate ratio 50:50. Silvafeed, a commercial tannin additive, was used
as a positive control. Nutrient intake was not di erent across the treatments, but nutrient digestibility
was a ected by dietary additives (p < 0.05). Compared to the control, and unlike the crude extract,
encapsulated-ATE and silvafeed did not reduce dry matter, organic matter, and neutral detergent
fibre digestibility. While the overall N-retention and total N-excretion (g/d) were not a ected by
dietary additives, ATE and encapsulated-ATE diets reduced urine-N excretion (g/d) and only a slight
reduction was observed in silvafeed diet. The faecal-N proportion was highest in the ATE diet
(388 g/kg N-intake), followed by encapsulated-ATE (317 g/kg), and silvafeed (267 g/kg), with the
control diet having the lowest proportion (230 g/kg). The acetate:propionate (A:P) ratio reduced as
a result of the inclusion of dietary additives with crude ATE and silvafeed having lower A:P ratio
compared to the control diet. Methane production expressed in g/kg dry matter (DM) intake was reduced by 12%, 30% and 19% in the silvafeed, crude ATE and encapsulated-ATE diets, respectively
(p < 0.05). The reduced methane production with higher neutral detergent fibre (NDF) digestibility in
the encapsulated-ATE, compared to the crude-ATE, confirms that encapsulated-tannin can be used as
an additive in ruminant diets.
