Growth Performance and Meat Characteristics of the First Awassi–Rambouillet Callipyge Backcross

SIMPLE SUMMARY: The Awassi sheep breed is very resilient in the Mediterranean region but shows poor meat quality. The callipyge mutation enhances growth and meat characteristics, and as such we bred Awassi-Rambouillet Callipyge carrier rams with Awassi ewes and compared meat quality in the first backcross of Awassi-Rambouillet callipyge carriers (CRAW), non carrier Rambouillet Awassi (RAW), and pure Awassi (AW) ram lambs in a fattening trial for 94 days. CRAW lambs showed mostly similar growth potential and meat characteristics to RAW lambs. However, CRAW lambs showed higher growth potential as compared to AW lambs, and better meat characteristics in the shoulders and legs, but not in tenderness. Fat tail weight did not change in CRAW as compared to AW lambs. Therefore, the introgression of the callipyge mutation in Awassi lambs allows for improvement in growth and meat, without impacting the currently desirable traits of the fat tail. This research allows the improvement of meat production and return on investment in the local flocks of Awassi sheep. ABSTRACT: 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.