عنوان مقاله [English]
In the present study, 9 rangeland species including; Acantholimon festucaceu, Cleome coluteoides, Convolvulus calverti, Eurotia ceratoides, Halothamus glaucus, Stipa barbata, Verbascum speciosum, Zygophyllum atriplicoides were sampled at three different phenological stages (vegetation, flowing, seeding) in 2009. All species belong to most important plant type of study site. Forage quality index namely; crude protein (CP), acid detergent fiber (ADF), dry matter digestiblility (DMD) and metabolism energy (ME) were determined to meet animal maintenance requirements. Analysis of variance was used to compare the index among species and different growth stages. Specific differences were evaluated by Duncan’s test. Results showed average crude protein for vegetating, flowering and seeding stages were 18.03, 14.13 and 9.12%, respectively. However, it was the highest in phenological stages and even lower than critical level (7.0%) to meet a animal unit maintenance requirement. Average dry matter digestible values for different phenological stages were 66.13, 60.29 and 52.72% with higher value for all phenological stages with values lower than critical amount (50%) to meet animal maintenance requirements in seeding stages. Metabolisme energy in vegetation, flowing and seeding stages were 9.24, 8.25 and 6.96 Mj/Kg/DM respectively with higher values for vegetation and flowering stage with values even lower than critical level (8Mj) to meet a animal unit maintenance requirement in seeding stages. This suggests that desirable quality of pasture forage at different times grazing is not same and determination of daily animal units requirement based on forage quality is needed. It is clear that forage quality is changed with variation of weather, but due to the expense of determination forage quality is very high, can use the results of this research for estimate of animal requirement in different years.