The current study was conducted in the Animal field of the Department of Animal Production – College of Agriculture - Al-Qasim Green University for the period from 10/10/2019 to 19/1/2020 to investigate the effect of addition of monensin at levels of 15, 30 and 45 mg/kg concentrate on growth performance of Awassi lambs. First treatment in which lambs were fed concentrate diet without addition of monensin was considered the control treatment. Sixteen male Awassi lambs were used with an average

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... ight of 24.85 and 4-6 months of age. The lambs were randomly distributed to the experimental treatments, four lambs per each using the individual feeding in the cages. The concentrate diet was offered at a level of 2.75% of the body weight at 2 meals, morning and evening meals, while the ground wheat straw was offered at free choice. Results revealed no significant effect of level of monensin on pH values, whereas ruminal ammonia concentrations were significantly decreased (P˂0.05) from 7.54 in the control treatment to 6.08 and 6.45 mg/100 ml due to addition of monensin at levels of 30 and 45 mg/kg. Moreover, addition of monensin at a level of 30 mg/kg concentrate diet significantly increased (P˂0.05) ruminal concentration of total volatile fatty acids to 13.76 as compared with 10.99 mM/100 ml for control treatment. Concentrations of all rumen fermentation characteristics were significantly affected (P˂0.01) by time of ensiling.