Department of Animal Sciences, College of Agriculture, University of Shiraz, Shiraz, Iran
Despite a shortage of animal feed in Iran, cereal stubble is often underutilized due to agro-economic reasons. On the other hand, lambs fed with a conventional fattening ration deposit a considerable amount of fat; therefore, this experiment was conducted aimed at better utilization of cereal stubble and reducing the fat content of lamb carcasses. Fat-tailed Mehraban and Ghezel ram lambs were put on four feeding systems (FS) for 100 days. Animals in one group (FS1) were lot-fed with a conventional fattening ration (4% of the mean body weight) consisting of 50% ground barley and 50% chopped alfalfa hay. FS2, FS3 and FS4 animals grazed stubbles, and in the evening, received 2% of their body weights either ground barley (FS2), a mixture (50:50 DM basis) of ground barley and alfalfa hay (FS3), or ground alfalfa hay (FS4). Daily gain, slaughter weight, and tail weight were greatest (P<0.05) for FS1, lowest for FS4, and intermediate for FS2 and FS3. Stubble-fed lambs had lower subcutaneous fat depth and cavity fat. The sum weight of lean in primal cuts was lower in FS4 as compared with other groups, but the lean weight as a percentage of carcass weight was lowest in SF1. Similar pattern was found for the dissected fat from the primal cuts. The weight of soft tissues was highest in SF1 and lowest in SF4, but its percentage in carcass showed a reverse pattern. Stubble feeding with some supplementary feed resulted in less fat deposition in fat-tailed lambs as compared with the conventional fattening ration, and was more economical in terms of unit live weight gain. Due to the feed shortage in Iran, stubble grazing should be encouraged in lieu of the current practice of burning the residues on the farm.