Effect of feedlot length on the carcass traits of male Afshari lambs

In order to study of the effect of feedlot periods (0, 60, 80, 100, 120, 140 days) on growth performance and carcass characteristic of the Afshari male lambs, 36 lambs were studied by completely randomized design (6 Treatments, with 6 Replications). Six lambs were slaughtered for carcass analysis at the beginning of experiment as the first treatment. Rations for the lambs of five other treatments were isocaloric and isonitrogenic, balanced by NRC(1985) recommendations. Lambs were fed individually 3 times daily. First body weight of lambs were considered as covariate for covariance analysis and data were analyzed statistically. Lambs' final weight were increased significantly according to increasing of feedlot periods, while there were not significant difference between the treatments of 120 and 140 days (p0.05). Bone percentage was decreased significantly by increasing of fattening period. Maximum bone percentage were observed at 60, 80 and 100 days , indicating rapid growth of bone at the beginning of animal life. Meat percentage was decreased significantly by increasing of fattening period so that maximum meat percentage was observed at 60 and 80 days, indicating the fast growth of muscle at short period of fattening of lambs. Total fat percentage was increased significantly by increasing the fattening periods, feed lot periods of 120 and 140 days had the most fat percentage with no significant difference showing the beginning of fat deposition in the animal body at short term fattening period and increasing the fat reservation at long term fattening period, all the items have allometeric growth. Tail fat percentage was the same as total amount of body fat so that it was increased significantly by increasing of feedlot period and maximum amount of it was found during 100, 120 and 140 days, but means did not differed significantly. Evisceral and subcutaneous fat amounts were in the same condition. Meat to fat ratio was decreased significantly by increasing of fattening period and the greatest ratios were observed in 60 and 80 days, and in longer the periods decrease of meat to fat ratio was obvious. By determining the mentioned characteristics, if the slaughtering weight is a standard for choosing of feedlot periods, 100 and 120 days feedlot periods were recognized as the better periods, but if market desirability, carcass quality, and percentage of meat and economical fattening is considered, and for avoiding of the feeding stuff convertion, specially grains, to body fat which is not desirable in the market, longer periods of fattening of lambs must be avoided. In practice the butchers commonly avoid buying the heavy sheep with high fat which cause the reduction of live body weight price. Therefore fattening periods of 100, 120 and 140 day are not suggested and maximum fattening period is 80 days, and if the meat price is not good in the market, it is better to reduce the fattening period toward the 60 days. Then, based on the obtained results, optimum body weight for slaughtering of fattening Afshari male lambs is 45.27±5.71 to 51.98±3.28 kgs.