The objective of this study was to investigate the effects of different forage and nohy; forage fiber sources on the performance, chewing activity, digestion, blood parameters of young lambs. Thirty lambs of Ghezel (average age of 2 days and average weight of 5.5 kg) were tested in completely randomized design with 3 treatments for 65 days (45 days pre-weaning and 20 days post-weaning). Experimental diet consist of: 1- control( with no fiber source; 2- starter containing 7% barley straw; 3- starter containing 15% sugar beet pulp.The lambs were weighted on d 45 and 65 after 14-16 h of fasting. Daily dry matter consumption of lambs fed control, starter containing 7% barley straw, starter containing 15% sugar beet pulp were 515, 596 and 596 g/d, which were affected by experimental treatments (P 0.05), so that the feed intake in starter diet containing straw beet pulp were higher than the control in post-weaning. Daily weight gain, weight in pre and post-weaning periods were not affected by experimental diet. Eating time, rumination and total chewing time were significantly higher in lambs fed starter containing straw than control and beet pulp (P 0.01). Dry matter, organic matter digestibility were the highest in the control diet. There was no significant difference in the pH of the ruminal fluid among treatments. Blood glucose concentration in lambs receiving the control and straw diet was higher than the beet pulp (P 0.05). Blood urea nitrogen and beta-hydrobutyric acid were not significantly different between treatments. Feeding fiber source in particular straw improved feed in take and chewing activity but had no effect on growth performance and decrease nutrient digestibility. Keywords: starter - fiber – beet pulp- suckling lambs – barley straw
