The nutritive value for ruminants of tagasaste ( Chamaecytisus palmensis), a leguminous tree

Abstract

The nutritive value of the leguminous tree tagasaste ( Chamaecytisus palmensis), commonly known as tree lucerne, was investigated in a series of experiments. The tree grows in dry environments, the leaves are highly palatable and on the basis of its chemical composition it would appear to have a role as a high quality feed source or supplement. 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. The CP content decreased significantly with time from 260 to 170 g kg −1 DM, but DMD did not change significantly (average in vitro DMD, 0.73). Most leaf senescence appeared to occur ∼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 day −1), prairie grass (151 ± 35 g day −1) and tagasaste (81 ± 36 g day −1). Subsequently, a cut and carry system was used to investigate the feeding value of tagasaste for lambs (27 ± 1.5 kg). Liveweight gain was 95 ± 30 g day −1. In a third experiment, the digestion of tagasaste leaf was examined in more detail by measuring the partitioning of digestion of DM, organic matter (OM), neutral detergent fibre (NDF) and crude protein (CP) in the digestive tract of lambs with duodenal and ileal fistulae. At high levels of feeding, there was a net loss of non-ammonia nitrogen (NAN) across the stomachs (30%) and an average NAN absorption across the small intestine of 68%. The average in vivo digestibility of DM, OM and NDF were, respectively, 0.77, 0.78 and 0.65, and the average proportion of in vivo digestion occurring in the stomachs was 0.55 and 0.80 for DM and NDF, respectively. In collating the results of all trials, it was observed that the DMD of leaf ranged from 0.71 to 0.78 and that of stem was 0.46 on average. The chemical composition of leaf was 210–240 g CP kg −1 DM and 300–370 g NDF kg −1 DM, whilst stem had values of 95 g CP kg −1 DM and 660 g NDF kg −1 DM. No significant levels of tannin were detected. A feature of these trials was the low Na content of the leaves, and marginal levels of P and S. No ill health was observed in any animal consuming tagasaste for periods of 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 (e.g., silage, brassica crops), but less than that of intensively managed temperate pastures. Its leaves were high in CP content and DM digestibility.