Effect of Fattening Season and Period on Feedlot Performance of Ghezel and Mehraban Lambs

This experiment was conducted using 172 male lambs of Ghezel and Mehraban breeds for two periods of 60 and 80 days. Two systems of fattening were studied. The first group of lambs entered feedlot boxes immediately after weaning (spring) but the second group being fed on pasture, entered the experiment approximately 4 months later (autumn). Fattening periods were 60 and 80 days. The average weaning age of lambs was 74.3±3.7 days. During the experiment, a pelleted finishing ration was fed ad libitum twice a day. The lambs were housed in individual boxes. Traits studied were birth and weaning weight, pre and post-weaning average daily gain, feed consumption and feed conversion ratio. The average weaning weight for Mehraban and Ghezel were 24.17 and 27.04 kg, respectively. The least square means of pre-weaning average daily gain for Ghezel and Mehraban were 299.5 and 267.9 g/day respectively. Average daily gain for Ghezel lambs were 260.3±19.7 and 218.8±19.8 g/day and for Mehraban were 233.3 and 195.6±19.2 g/day during spring and autumn fattening, respectively. Feed conversion ratios for Ghezel were 6.94±0.59 and 7.96±0.59 while they were 7.48±0.55 and 8.77±0.58 for Mehraban during spring and autumn, respectively. The least square means of daily feed consumption, average daily gain and FCR during the 60-day fattening were 1.84±0.03 kg, 249.7±7.9 g/day and 7.43±0.24, respectively. The corresponding values for 80-day fattening were 1.59 kg, 204.3±5.7 g/day and 8.15±0.17, respectively. Interaction effects of year×breed, season×breed and season×duration of fattening were not found as significant. Age and weight of ewe did not significantly affect the on fattening performance of lambs