Native drought-tolerant range perennial shrubs (Alhagi camelorum Fisch, Salsola vermiculata L. and Peganum harmala L.) and herbaceous range plants (Poa sinaica Steud, Erodium cicutarium L. and Schismus arabicus Nees) grown naturally on the south-eastern semi-desert of Syria and harvested in the early bloom stage or in seed stage were evaluated in terms of some of their nutritive components (crude protein, ether extract, crude fiber, ash and gross energy), cell wall constituents [neutral-detergent fiber (NDF), acid-detergent fiber (ADF) and lignin] and nitrogen forms [buffer soluble nitrogen (BS-N), buffer soluble non protein-nitrogen (BS-NPN) and buffer soluble protein nitrogen (BS-PN)]. In vitro digestible organic matter (IVDOM), metabolizable energy (ME) and net energy lactation (NEL) after incubation with or without polyethylene glycol (PEG, 6000) at a ratio of 2:1 PEG/substrate were studied utilizing an in vitro incubation technique with rumen fluid.
The values of the nutrient components, cell wall constituents, nitrogen forms, IVDOM, ME and NEL varied with the experimental range plants studied. The shrubs studied had a high concentration (199 g/kg DM) of crude protein, whereas the herbaceous range plants had a low concentration (94 g/kg DM). The lower concentrations of crude fiber, NDF and ADF were in S. vermiculata and P. harmala (161, 266 and 190 g/kg DM, respectively), whereas the highest concentrations were in A. camelorum, P. sinaica, E. cicutarium and S. arabicus (289, 573 and 351 g/kg DM, respectively). S. vermiculata had a low concentration of gross energy (12.1 MJ/kg DM). The early harvest of S. vermiculata and P. harmala had high values of crude protein and low values of crude fiber and cell wall constituents than the late harvest. The highest value of the ME was obtained for P. sinaica and E. cicutarium and the lowest for A. camelorum and S. vermiculata harvested in the seed stage. S. vermiculata and P. harmala had high concentrations of BS-N, whereas P. sinaica, E. cicutarium, S. arabicus and A. camelorum had lower concentrations. The ME and NEL values of the experimental plant species amounted to 5.81-7.65 and 1.35-4.14 MJ/kg DM, respectively. The response of the range plants to PEG treatment varied between species and changed over time. The IVDOM, ME and NEL values increased from 573 to 638 g/kg DM for IVDOM, from 6.86 to 7.86 MJ/kg DM for ME and from 3.21 to 4.01 MJ/kg DM for NEL when the PEG was present in the incubation medium. The early harvest range plants had higher values of IVOMD, ME and NEL than the late harvest. Crude fiber and NDF were negatively correlated with IVDOM, BS-N, BS-NBN and crude protein. Native range plants are recommended for ruminants to cover the major part of their nutrient requirements.