Effect of non-encapsulated and encapsulated mimosa (Acacia mearnsii) tannins on growth performance, nutrient digestibility, methane and rumen fermentation of South African mutton Merino ram lambs

Abstract

The use of mimosa tannins as feed additives in contemporary ruminant nutrition studies has gained wider acceptance, because of their potential to reduce enteric methane and enhance dietary protein utilization. However, tannin’s astringency and quick dissolution decrease feed intake and digestibility. Microencapsulation technology could be adopted to neutralize the astringency and ensure controlled tannin solubility across ruminant digestive tract. The present study examined the influence of supplementing unencapsulated and encapsulated Mimosa (Acacia tannin) tannins on growth performance, digestibility, methane (CH4) and rumen fermentation in South African mutton Merino sheep. A total of 40 weaned Merino ram lambs of 96 days old (34 −35 kg body weight, BW) were randomly allocated to one of the four dietary treatments in a randomized complete block design as follows: total mixed ration, (T1, TMR alone); TMR + Monensin at 75 mg/kg feed dry matter, DM (T2, Monensin); TMR + unencapsulated Mimosa tannin at 20 g/kg DM (T3, UMT) and TMR + encapsulated Mimosa tannin in sunflower oil at 20 g/kg DM equivalent (T4, EMTS). The lambs were adapted to the diets over a period of 28 days thereafter, feed intake and weight changes were recorded for 77 days. The lambs were moved to metabolic crates and assessed for digestibility followed by methane measurement in open-circuit respiratory chambers. Finally, the animals were slaughtered, rumen fluids sampled and analysed for volatile fatty acids (VFAs) and ammonia nitrogen (NH3-N). Inclusion of UMT and EMTS did not affect (P > 0.05) feed intake and weight gain. Compared with the TMR alone, UMT and EMTS increased intake of DM (T1, 1328 g/day vs T3, 1578.1 and T4, 1569 g/day; P = 0.05), DM adjusted to BW (T1, 69.3 g/kg BW vs T3, 83.8 and T4, 83.7 g/kg BW; P = 0.04), organic matter, OM (T1, 1254 g/kg vs T3, 1494 and T4, 1490 g/day; P = 0.04), neutral detergent fibre, NDF (T1, 344 g/day vs T3, 434 and T4, 416 g/day; P = 0.01) and acid detergent fibre, ADF (T1, 174 and T3, 241 g/day vs T4, 218 g/day; P = 0.02), compared with the control. However, only UMT decreased (P = 0.01) digestibility of DM (T3, 640 g/kg vs T1, 746 g/kg), OM (T3, 655 g/kg vs T1, 761 g/kg) and CP (T3, 734 g/kg vs T1, 829 g/kg). Furthermore, UMT increased (P = 0.01) faecal nitrogen (N) excretion (T3, 13.7 g/head/day vs T1, 8.03 g/head/day and T3, 266 g/kg N-intake vs T1, 171 g/kg N-intake). UMT and EMTS reduced CH4 in g/kg DM-intake (T3, 15.3 and T4, 14.8; vs T1, 18.9; P = 0.04). However, NH3-N and total VFAs concentrations were not influenced (P > 0.05) by the inclusion of UMT and EMTS. It was concluded that UMT and EMTS could be utilized in mitigating enteric CH4 while enhancing nutrient intake when supplemented at 20 g/kg DM of feed. Among the two, however, EMTS reduced more CH4 without affecting digestibility compared to equivalent proportion of UMT. Further studies should be conducted on the total tannin concentration of the encapsulated mimosa tannin in sunflower oil.