عنوان مقاله [English]
Introduction: Demands of agricultural products, particularly in developing countries, are increasing rapidly. Consequently, land and water resources are unable to sustain such demands. For decades, rangelands in Africa, West and Central Asia suffered from overgrazing and many areas are severely degraded. Range vegetation used to be the main feed resource for livestock particularly in the arid and semi-arid regions such as Iran. Soil and water salinity is another major constraint affecting dry land agriculture and following animal production as soil salinization is a major environmental problem in Iran. Climate change, human activities, reduced vegetation and a rising water table are contributing to expansion of saline soils worldwide. Halophytic plants can be regarded as feed resources for ruminants in Iran as identiﬁed 354 different species growing on highly saline sites. These plants are naturally grown or cultivated in salt affected lands such as in saline semi-deserts and could have great potentialities particularly as sources of livestock fodders. However, wide intra- and inter-plant species variations in productivity, palatability, chemical composition, and nutritive value depend on seasonal changes, environmental conditions and management practices. Salt marsh plants, in particular chenopods forages, are relatively low in metabolizable energy and high in ash content. Data derived from many studies, on average values of chemical composition, crude ﬁber (3.4 to 14 percent) and dry matter digestibility (more than 60 percent) of most dominant halophytes in the Near East region have been determined. The aim of the study was to assess nutritive value of three most dominant halophytes in Semnan Province through determination of chemical compositions, in situ degradability and in vitro gas production techniques.
Materials and Methods: Nutritive value of Atriplex (A. canesences), Salsola (S. rigida) and Aeluropus (A. littoralis) were evaluated through determination of chemical compositions, in situ degradability and in vitro gas production techniques using three fistulated steers. The samples were collected at seed ripening period from Research Station in arid zone of Semnan Province and analyzed for chemical composition including crude protein (CP),ether extract (EE), ash, neutral detergent ﬁber (NDF), acid detergent ﬁber (ADF), Ca, P, Na, K, Mg, Cl and S contents. Then, the samples were tested in an in vitro gas production method (96 h incubation) and batch rumen culture system (24 h incubation). The asymptotic gas production system (A) and lag time (L) parameters and also in vitro DM disappeared (IVDMD), organic matter digestibility (OMD), metabolizable energy (ME), short chain fatty acids (SCFA), N-NH3 content and pH were calculated. Subsequently, to determine the nutrients degradability of the plants, three fistulated steers were used. Approximately 5 g of each ground plant was weighed into Dacron bags with a pore size of 50 µm. Bags were incubated for 0, 2, 4, 6, 8, 12, 24, 36, 48, 72, 96 and 120 h in the rumen. Zero-hour bags were only presoaked and washed. After rumen incubations, bags on were rinsed immediately with cold tap water, washed and dried at 60 ºC for 48 h to determine DM degradability. The residues from incubation time were used for determination of nutrient content (CP and NDF). Rumen degradation parameters of CP and NDF were estimated using the NLIN procedure of SAS.
Results and Discussion: All of these halophytic plants had high concentrations of Na, K, and Cl, and low levels of Ca, P and Mg. Moreover, the CP and ash contents of these plants were considerably high. It would be noticed that much of halophyte nitrogen is associated with non-protein compounds such as nitrates, glycine, betaine and proline. Other reports showed Atriplex shrubs contained higher level of ash. This result might be attributed to effects of salinity on cation accumulation as concentrations of some minerals in Atriplex spp. are higher than those recommended for ruminants and seem to reduce voluntary feed intake. There are variation between our found with results from other studies which is attributed to the difference in species, geographical regions, seasons and soil type. The asymptotic gas production system (A) and lag time (L) parameters were highest for Aeluropus. Also, OMD, ME, and SCFA parameters in Aeluropus were higher than Atriplex and Salsola. Furthermore, significant increase in gas produced after 96 h incubation was observed with Aeluropus in comparison to other plants. These results indicate that higher protein and lower NDF contents in Aeluropus may be attributed to different in gas production parameters. The amounts of OMD and ME were in line with results in other reports. However, the average fermentation rate (AFR) and pH were similar for halophyte plants. The rapidly degradable fractions of DM and CP of Salsola (28.42 and 55.68 %) were higher than those for Atriplex (23.24 and 48.7 %) and Aeluropus (21.50 and 51.28 %) which is associated with lower NDF and higher Ash contents in Salsola. On the other hand, degradability potential of DM and NDF of Aeluropus (52.42 and 75.82 %, respectively) were higher than those for Atriplex and Salsola. Moreover, Salsola showed the lowest effective degradability for NDF as measured at different outflow rates.
Conclusion: Overall halophyte plants were high in ash (Na, Cl and S) and CP but low in energy. Salsola plant may have better palatability because of lower NDF content and more soluble fraction (a) than to Aeluropus and Atriplex. The measured data in this study suggest that these halophytic plants can be regarded as feed resources for ruminants in the arid zones of Iran.