Plant growth development effect on amount of forage quality parameters in Sabalan mountain rangelands

The determination of nutritional value of range plants is essential to assess the available energy for animals at different growth stages, recognition of correct grazing time and increasing animal yield without damage to range plants. In this study, four species including; Alopecurus textilis, Festuca sulcata, Poa trivialis, Bromus tomentellus were sampled in three phenological stages (initial growth, flowering & seeding) in 2008. Quality parameters such as crude protein, acid detergent fiber, dry matter digestibility and metabolisable energy were calculated based on AOAC (2000) instruction. A one-way ANOVA was used for comparing the quality parameters of species and phenological stages, and Duncan’s Multiple Range Test was used to determine the source of variations within groups. Results showed that the mean amounts of crude protein at different growth stages were 9.96, 8.18 and 6.09 percent, respectively that in initial growth and flowering stages were higher and at final growth stages were lower than the approximate amount of critical level (7%) for supplying the daily requirement of animal unit (50 Kg sheep). The mean amounts of digestibility at different growth stages were 51.34, 46.86 and 41.69 percent, respectively which were higher at vegetative growth stage and lower at flowering and seeding stages than the critical level (50%) for one animal unit maintenance. The amounts of metabolizable energy at different growth stages were calculated to be 6.73, 5.97 and 5.09 Mj/KgDM respectively that their amounts at all growth stages were lower than the approximate critical level (8 Mj) for supplying the requirement for one animal unit. These results represent that the favorability of rangeland forage quality is not same in different growth stages and determining the daily animal unit requirement on the basis of forage quality is needed. Overall, studied species in terms of crude protein supplying, especially at initial growth stages, were evaluated as favorite but in terms of supplying the daily metabolizable energy requirements of grazing animal in region, had less favorability.