The nutritive and feeding value of tagasaste (Chamaecylisus palmensis)

Abstract

Tagasaste (Chamaecytisus palmensis) is a leguminous tree which grows well in dry environments. Anecdotal reports exist on its good feeding value for livestock but no systematic study appears to have been done to investigate this. In this thesis, studies were initiated into the digestibility and chemical composition of newly emerged leaves and the effect of leaf maturity on these parameters, the feeding value in terms of liveweight gain of lambs and finally the partitioning of nutrient digestion in the digestive tract of lambs consuming tagasaste particularly in relation to duodenal protein supply. In the/first experiment, leaf buds were tagged in spring and the effect of leaf maturity on crude protein content (CP) and in-vitro dry matter digestibility (DMD) investigated. CP content L decreased significantly (P<0.05) with time from 26% to 17% but DMD did not change significantly (average in-vitro DMD, 0.73). Most leaf senescence appeared to occur approximately 5 months after leaf emergence. In the second experiment of 6 weeks duration the liveweight gain of lambs (23 ±1.5 kg) browsing tagasaste, and grazing lucerne or prairie grass was examined and the order of response was lucerne (265 ±33 g/d), prairie grass (151 ±35g/d) and tagasaste (81 ± 36g/d). In a third experiment of 9 weeks dut:ation, a cut and carry system was used to investigate the feeding value of tagasaste for lambs (27 .5 kg) and liveweight gain was 95 ± 30g/d. The in-vivo DMD of tagasaste was 0.69(±0.004) and animals consumed 27(±5.1) g digestible organic matter (DOMI)/kg W/ d of which 72 % of the dry matter intake was leaf. The i11-virro DMD for leaf (0.77) and stem (0.46) indicated that if high animal performance is to be achieved, then the animals must consume mostly leaf. A feature of these trials was the low Na content of the leaves and marginal levels of P and S. Animals had free access to salt blocks but the extent to which these minerals influenced the liveweight gain response is not known. In the fourth experiment the digestion of tagasaste was examined in more detail by investigating the pm·titioning of digestion of DM, OM, NDF, and protein in the digestive tract of lambs with duodenal and ileal. fistulae. The most important finding was that duodenal NAN supply was lower than that in it . other temperate pasture which promote high liveweight gain (ad-lib tagasaste 0.8 g NAN/kg W/d and 31 g NAN/kg DOMI). These results help explain the poorer performance of animals consuming tagasaste compared to those grazing lucerne and prairie grass. At high levels offeeding, there was a net loss of NAN across the stomachs (30%) and an average NAN absorption across the small intestine of 68%. This suggests that tagasaste has potential as a protein supplement for animals consuming low quality roughage. All digestion parameters changed with increasing level of feeding but the average i11-vivo DMD, OMD and NDFD were respectively 0.77, 0.78 and 0.65 and the average proportion of in-vivo digestion occuring in the stomachs was 0.55, 0.49 and 0.8 for DM, OM, and NDF respectively. These values were not ·" markedly different to values recorded for other temperate forages. In collating results of all trials, it was observed that DMD of leaf ranged from 0.71-0.78 and that of stem on average was 0.46. Other values for leaf were CP 21-24% and NDF 30-37%, whilst stem had values for CP of 9.5% and NDF of 66 %. No significant levels of tannin were detected. No ill health was observed in any animal consuming tagasaste for periods up to 9 weeks. It was concluded on the basis of the liveweight gain response that tagasaste had a feeding value similar to other conserved forages (eg. silage, brassica crops) but less than that of intensively managed temperate pastures (eg.lucerne, prairie grass).