Nutritional value of Chamaecytisus palmensis (tree Lucerne) browse at different growth stages

Abstract

Chamaecytisus palmensis (tree Lucerne) is a multipurpose tree, which is cultivated mostly for supporting protein nutrition in livestock. Tree Lucerne also serves a critical role in human nutrition and ethno pharmacology. Most tree parts are browseable hence the increase in research focus to optimise utilization of this forage resource. The objectives of this study were to (1) evaluate effects of stage of growth (early-bloom and post-bloom) and postharvest drying method on chemical composition, structural carbohydrate fractions and relative forage value of browseable leafy and woody components of tree Lucerne; (2) Evaluate of drying mature herbage (post-bloom) on rumen degradability of edible components. Tree Lucerne was harvested in Bela Bela, Limpopo province, South Africa in 2016. Leaves, twigs (< 4 mm) and stems (< 8 mm) were harvested during early-bloom (EB) and post-bloom (PB). Samples of the leaves, twigs and stems were partitioned for whichever air-drying, sun-drying or no drying (fresh material-control) treatment in a complete randomised design yield the following treatments: EBLf (early-bloom fresh leaves); EBLa (early-bloom air-dried leaves); EBLs (early-bloom sun-dried leaves); EBTf (early-bloom fresh twigs); EBTa (early-bloom air-dried twigs); EBTs (early-bloom sun-dried twigs); EBSf (early-bloom fresh stems); EBSa (early-bloom air-dried stems); EBLs (early-bloom sun-dried stems); PBLf (post-bloom fresh leaves); PBLa (post-bloom air-dried leaves); PBLs (post-bloom sun-dried leaves); PBTf (post-bloom fresh twigs); PBTa (post-bloom air-dried twigs); PBTs (post-bloom sun-dried twigs); PBSf (post-bloom fresh stems); PBSa (post-bloom air-dried stems) and PBLs (post-bloom sun-dried stems). Proximate analysis was done to assess compositional changes caused by drying of EB and PB portions; equations of Traxler et al. (1998), Weiss (2004), and Van Soest (1994) and Fox et al (2003) were applied to estimate composition of structural and non-structural components. In sacco dry matter degradation of PB materials was done to deduce effective degradability. Proximate and degradation data was applied in estimating relative feed value. Nutritional value of leaves: Early-bloom leaves: Crude protein content of EB leaves varied within treatment (21-28% DM) with highest level in EBLa and lowest in EBLs. Air-dried and EBLf contents were low in fibre and varied from 21.1-28.7% NDF DM respectively. Non-fibre carbohydrates (NFC) were high (up to 52.6% DM) with highest level in EBLs and lowest in EBLf. Lignin and indigestive CP were both < 2% and 5%, respectively. Leaves had mean of 87.1% TDN, 3.0-3.5 Mcal/kg ME with estimated dry matter intake of 5.7% and relative feed value/ index of 372. The EBLa had the highest forage quality. Post-bloom leaves: Mean crude protein was 23.2% DM and differences were not observed within treatments. Leaf NDF ranged between 23.2-36.6% DM inversely related to NFC contents (45.7- 49.1%). Lignin content and indigestive CP were < 3%. Leaves varied between 81.5-89.4% TDN, 2.8-3.4 Mcal/kg ME, 213.1-339.3 of RFV with 3.3-5.2% estimated DMI. Although, difference was observed within treatments, PBLa had high RFV and DMD. Mean DMD and NDFD was 81.7 % DM and 66.5% DM respectively with no difference across treatments. Nutritional value of twigs: Early-bloom twigs: Although, CP content of twigs varied between 9.8-17.1% DM, no differences were observed. Twigs had 40.7- 48.7% NDF DM. Indigestible CP (ADFICP) was 2% DM. Mean NFC was 26.7% DM and the indigestible fibre CHO was higher in EBTf 42.6% and lower in EBTa (29.8%). The EBTa had the highest RFV (176.7) compared to EBTs (156.3) and EBTf (140.3). Post-bloom twigs: twigs ranged between 48.3-51.5% NDF DM, 5.7-16.7% CP DM, with greater proportions in PBTf. Mean NFC was 21.7% DM, which related to higher indigestible fibre CHO (29.8; 37.3 and 46.1% DM in PBTa, PBTs and PBTf, respectively). The RFV was low. The PBTa had the highest DMD (63.2%) and NDFD (49.4%) while PBTf was least degradable. Nutritional value of stems: Early-bloom stems: Mean CP of stems was 11.5% DM and did not vary. NDF was greater in EBSf (54.9% DM NDF) and least in EBSa (35.7% NDF DM). Lignin content was low in dried material, but about 11% in EBSf associated with higher indigestible CHO C content (46% vs 23.7% DM in EBSa). The EBSa had high NFC content (37.4% DM) and lower in EBSs (7.4% DM). The estimated DMI was < 1.4% BW. Post-bloom stems: Drying treatment did not affect crude protein contents, which varied between 8.3-11.6% CP DM. Indigestible CP was 0.3-1.7% DM and NFC were 3.1-18% DM. Drying did not affect DMI and RFV index. At 48h of incubation, DMD was about 56% DM, in the order PBSs< PBSa< PBSf. The NDFD component was between 38-51% NDF. Findings of this study show that there were less changes in NSCHO components loss, which are essential sources of nutrients.