The Awassi breed is desirable due to its resilient traits, but shows poor lean meat content on the carcass; the callipyge mutation may enhance growth and meat characteristics. The first backcross of callipyge Awassi–Rambouillet (CRAW) lambs was generated by mating Awassi ewes with heterozygous F1 (50 % Awassi and 50 % Rambouillet) rams for the callipyge mutation. A fattening trial with carriers of CLPG (CRAW), non-carriers (RAW), and Awassi (AW) ram lambs was conducted for 94 days and growth and meat characteristic parameters were recorded. Final body weight, average daily gain (ADG), feed conversion ratio, and dry matter intake, but not initial body weight, were greater in CRAW and RAW lambs as compared to AW lambs; hot and cold carcass, dressing percentage, and shoulder, rack, and loin weights were greater in CRAW vs. AW but not RAW lambs. Leg cuts were heavier in CRAW vs. both RAW and AW lambs; intermuscular and subcutaneous fat percentages were greater in CRAW as compared to AW but not RAW lambs. Non-carcass components showed kidney fat, kidney, liver and testes weights higher in CRAW lambs as compared to AW lambs, but these parameters were similar to those of RAW lambs. There were no differences in fat tail weight. Further, CRAW lambs had higher shear force and water holding capacity than RAW and AW lambs, while cooking loss was the lowest in CRAW lambs. In conclusion, the callipyge mutation with 25% Rambouillet genes can provide efficient improvements in growth and meat characteristics, with the exception of tenderness in Awassi sheep.

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The association between the ovine calpastatin gene (CAST) genotypes, growth performance and meat characteristics of Awassi sheep was investigated. Homozygous (MM) and heterozygous (MN) genotypes of the CAST were obtained by RFLP, using Awassi ram lambs (age=7 to 14 days n= 80).A fattening trial was conductedusing 10 ram lambs MspI - of CAST genotypes (5 lambs from each genotype) (homozygous (MM) and heterozygous (MN). Lambs were weighed at the beginning of the experiment and the subsequent weights were measured biweekly before the morning feeding throughout the duration of the experiment. At the end of the fattening period, all lambs were slaughtered to evaluate carcass characteristics and meat quality. The results showed a significant association between CAST genotypes and growth rate and final body weight showing that lambs of the MN genotype had a higher average daily gain and final body weight compared to lambs of the MM genotype. The CAST gene genotypes showed a significant effect on some carcass components and meat quality parameters indicating that MN genotype showed lower total bone and higher meat to bone ratio than the MM genotype in the dissected leg cut. Furthermore, the MN genotype had a higher longissimus muscle weight compared to MM animals. Meat quality analysis showed that MN genotype lambs had higher shear force, lower cooking loss and lightness. It can be concluded that the CAST gene can be considered as one of the genes that control growth performance and meat quality traits.