Determination of Chemical Composition, Gas Production Parameters and in vitro Digestibility of Astragalus podolobus in Different Phenological Stages and Comparison with some Halophyte Plants

[ Endemic plants of rangelands, especially key species and palatable ones are inevitable for improvement and development of rangelands. The grazing is a critical managing factor regarding to the resources conservation and quantitative and qualitative increase of plants production at the rangeland ecosystems. Rangelands are dynamic ecosystems and changing as a result of the environmental disturbances. Sustainable utilization of rangelands is obtained when the changes become known. The increase in population over the past few decades, due to the increased demand for livestock production, has increased the number of livestock in the rangeland, and as a result, the pressure on the rangelands, especially in arid and semi-arid areas, has damaged many rangelands. After the degradation of rangelands, one-year species, non-palatable and toxic species are replaced by the high quality and palatable species and therefore the quality and quantity of forage in most of the rangelands is by no means satisfactory. Many rangelands in arid and semi-arid regions have been affected by soil erosion and dust and greasy vegetation due to the lack of vegetation. In the vast array, rangelands cultivating non-domestic species have been imported, For example, in dry and semi-arid rangelands of northern of Golestan province, imported species of Atriplex cultivate which, despite proper forage production and other benefits, has some disadvantages, including gradual increase of soil salinity, lack of plant regeneration in the years after establishment which cause metabolic disorders in animals, negative effects on native plants, parasite organisms in planting areas and the destruction of the plant due to extreme cold, which will undoubtedly lead to an increase in economic costs after its destruction, as well as reducing fodder production. Therefore, in order to improve and revitalize dry and semi-arid rangelands, it is necessary to introduce, reproduce and deploy indigenous species with high adaptability and high yield.

Plant samples in different growth stages (vegetative, flowering and seeding) were collected from arid and semi-arid hilly loess soil located north of Golestan province, Gonbad-e Qabus (Dashli Borun). The Gonbad-e Qabus is located (55o 12 N, 37o 16 E) and 45 m above sea level. The mean annual rainfall amount is below 450 mm and mean annual temperature is above 20 °C. Samples of Astragalus podolobus, Atriplex (A. canesences), Salsola (S. rigida), Lyceum, Artemisia sieberi were taken and air dried at 60 °C for 48 h and milled to pass a 1 and 1.5 mm screen. Their nutritive value was evaluated through determination of chemical compositions and in vitro gas production techniques. Samples were tested in an in vitro gas production method (96 h incubation) and batch rumen culture system (24 h incubation). Rumen fluid was collected before the morning feed from three fistulated Dalagh male sheep (45 ± 2.5 kg live weight fed on a forage diet at a concentration of 40:60). In vitro gas production was measured in triplicate and for each replicate, a sample of 200 mg DM were used. The bottles were then filled with 30 ml of incubation medium that consisted of 10 ml of rumen fluid plus 20 ml of buffer solution and placed in a water bath at 39 °C. Gas production was recorded at 2, 4, 8, 16, 24, 48, 72 and 96 h. Total gas values corrected for blank incubation and gas values expressed in ml g-1 of DM. The asymptotic gas production system (A) and rate of gas production (c), organic matter digestibility (OMD), metabolizable energy (ME) and short chain fatty acids (SCFA). A medium similar to one developed for gas production was used for batch rumen culture system to measure pH, and NH3-N and in vitro digestibility. The pH of the media was measured after 24 h incubation. After 24 h incubation, the contents of each glass bottle were empty, strained through four layers of cheesecloth and then 10 ml of strained rumen fluid was acidified by 10 ml of 0.2 N HCl for determination of NH3-N using the distillation method. Finally, all contents remaining in the bottles were filtered through nylon bags, oven dried at 60 °C for 48 h and analyzed for IVDMD and IVOMD.

Results showed that there were significant differences among plants species for chemical composition. The OM content ranged from 63.77 to 89.33% for all species and Artemisia sieberi had highest and salsola had lowest at seedling stage. The results of the present study showed that there were significant differences among plants species on potential and rate of gas production. Artemisia sieberi and Atriplex canscens had highest potential gas production at flowering and seedling, respectively. Salsola had lowest OM digestibility, ME and ACFA concentration. There were significantly differences among different species on DM digestibilty vegetative stage and Artemisia sieberi and Atriplex had highest (58.66 %) and lowest (50 %) DM digestibilty, respectively. Salsola showed the highest value of partitioning factor at vegetative stage(7.37 mg/ml) and lycium showed the lowest value of partitioning factor at seeding stage (3.42 mg/ml).

In conclusion, results of current study showed that Astragalus podolobus has nutritive value as similar as Artemisia Sieberi. However, further investigation is needed in order to determine nutritive value of these species.