This experiment was conducted to investigate the effect of different natural zeolite (clinoptilolite) levels on average daily gain (ADG), dry matter intake (DMI), feed conversion ratio (FCR) and carcass characteristics in Varamini lambs. Forty eight male and female (average body weight 24.68±1.58 Kg (males) to 23.42±2.11 Kg (females) and age of 165±10 days (males) to 173±5 days (females) were studied as a complete randomized block design, the sex in lambs being taken as block. The lambs were fed by total mixed ration (TMR) as ad-libitum individually. The trial treatments included 0 % zeolite (Z) with 0 % urea (U), 1.5 % Z with 1 % U, 3.5 % Z with 1 % U and 5.5 % Z with 1 % U. At the end of the experiment all male lambs were slaughtered and their carcasses physical and chemical compositions determined. Feed sample analyses for dry matter (DM), crude protein (CP), ether extract (EE) and neutral detergent fiber (NDF) were carried out. Apparent digestibilities were determined through fecal collection method. The results indicated that ADG and FCR were improved by zeolite and urea addition. The lambs which received the 3.5 % Z and 1 % U had the highest ADG (168.63 gr) and the best FCR (7.74) while the lambs that received control diet had the lowest ADG (152.53gr) and the lowest FCR (8.16). Average DMI was not affected by dietary treatments, although it tended to be increased by addition of zeolite. Carcass weights were not affected by dietary treatments, although they tended to be increased by addition of zeolite. Average CP%, CP/EE ratio and ash % of boneless 10-11-12th ribs were significantly (P<0.05) affected by dietary treatments. The 5.5 % Z had the highest CP % (15.67 %), while control containing the lowest (14.31%). Zeolite (clinoptilolite) supplementation decreased EE % while increasing ash percentage in the 10-11-12th boneless ribs.
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