M.R Javanmard - Department of Veterinary and Food Hygiene; University of Scientific-Applied, Arak, IRAN.
M Kazemi-Bonchenari - Department of Animal Science, Faculty of Agriculture and Natural Resources, Arak University, Arak, IRAN.
S Afshar - Institute of Scientific-Applied Higher Education of Jihad-e-Agriculture- Agricultural Research, Education and Extension Organization, Tehran, IRAN

To identification of optimum initial live weight (ILW) and sex effect for fattening of Iranian Lori-Bakhtiari breed, a total of 224 growing lambs were allocated in two separate experiments. The first experiment (n = 144) was conducted to study the optimum initial live weight for more efficient fattening program. The second experiment 80 lambs (40 male and 40 female lambs) was used to investigate the effect of sex of this breed in fattening program in intenstive rearing system. In the first experiment, 144 ram lambs allocated in three different treatments (48 animals per each) with different ILW; T1) 23.2, T2) 27.3 and T3) 32 kg. In the second experiment 80 lambs were assigned in two different treatments (40 male and 40 female lambs as M and F treatments, respectively). Feed intake (FI), average daily gain (ADG) and feed converion ratio (FCR) were determined in both experiments. The first experiment lasted 110 days and the second experiment lasted 100 days. Considering the results for experiment one showed that the best value for FCR was gained when the lambs were fattened at ILW of 23.2 kg and the best ADG also was gained in 27.3 kg ILW. Based on the first experiment, the ILW of about 27 kg could be recommendable for starting the fattening in Iranian Lori-Bakhtiari lambs. Considering the second experiment results show that male lambs had better gain (285 vs. 207 g/d) (P < 0.05) and alsolower feed conversion rate (6.31 vs. 6.42) (P < 0.05) in similar age andweight compared to female lambs. This study indicate that malelambs with intitial live weight of 27 kg might be recommendablefattening program in intenstive rearing system.

Feed conversion ratio, Initial live weight, Lori-bakhtiari sheep breed