| چکیده انگلیسی مقاله |
The present study was conducted to determine the appropriate fattening age for Afshari lambs. For this purpose, 24 male Afshari lambs were divided into four age groups (60, 90, 120, and 150 days) with average initial weights of 22.83 kg, 27.73 kg, 36.30 kg, and 42.55 kg, respectively, in a completely randomized design. The objective of this experiment, based on a previous study, was to achieve a slaughter weight of 50 kg in the shortest possible time. The results showed that the average slaughter age of the experimental groups differed significantly, with lambs fattened at 60 and 90 days of age having a lower slaughter age compared to the other groups (P < 0.05). The effect of fattening start age on weight gain was significant, with the 90-day group showing the highest daily weight gain (333 grams) (P < 0.05). There was a significant difference in dry matter intake among the experimental groups, with the lowest intake observed in the 60-day group (1.31 kg), which increased with age (P < 0.0001). As the fattening start age increased, the feed conversion ratio significantly increased, with the highest value in the 150-day group (7.72) and the lowest in the 90-day group (4.48) (P = 0.0003). Neck weight differed significantly among the groups, with values of 0.848 kg, 0.693 kg, 0.975 kg, and 0.770 kg for the first, second, third, and fourth groups, respectively (P < 0.0001). The weights of the shoulder, breast, thigh, and loin were similar among the groups and did not differ significantly. However, the weight of the tail fat was significantly higher in the 60- and 90-day groups compared to the 120- and 150-day groups (3.063 kg and 3.200 kg vs. 2.085 kg and 2.427 kg, respectively) (P = 0.0029). Hot carcass weight and cold half-carcass weight did not differ statistically, but the highest cold carcass weight was observed in the first group (60-day start, 26.683 kg), and the lowest was in the third group (120-day start, 23.933 kg). The weight of meat and bone in the cold half-carcass did not differ significantly among the experimental groups. Subcutaneous fat weight was significantly lowest at 120 days and highest at 90 days (P = 0.0152), while intermuscular fat weight in the cold half-carcass was similar among the groups (P > 0.05). However, total fat weight, including visceral fat, in the cold half-carcass differed significantly (P = 0.0500), being higher in the 60- and 90-day groups (5.218 kg and 5.300 kg, respectively) compared to the 120-day group (4.347 kg), with the 150-day group (4.626 kg) showing no difference from the other groups. The lowest slaughter age was observed in lambs fattened starting at 90 days, which was significant (P < 0.05). Overall, it can be concluded that the optimal fattening start age for male Afshari lambs, considering carcass composition and cost-effectiveness, is 90 days, with a starting weight of approximately 27 kg. |