Effect of Polymorphism of Calpastatin gene, Age on meat Tenderness for Carcasses in Local Awassi sheep

ABSTRACT
This study was conducted in the livestock farm, College of Agriculture, University of Baghdad and the Genetic Resources Laboratories Unit, Animal Resources Department, Ministry of Agriculture and Biotechnology Research Center, AL-Nahrain University. The study was carried out during the period from Mid-July 2014 to 1st April 2015. The aim of the study was to determine the genotypic polymorphism of Calpastatin (CAST) gene and its association with a number of qualitative characteristics of sheep meat of local Awassi sheep carcasses, considering the effect of the animal sex. The study utilized 40 animals of local Awassi sheep; 20 males and 20 females, from which blood and tissue samples (Longissimus dorsi muscle, LD, and Biceps femoris muscle, BF) were collected. After DNA collection from blood samples, polymerase chain reaction (PCR) technique was followed using the primer of Intron I from L domain of the ovine calpastatin gene, which resulted in a full amplicon length of 565 bp fragment. The PCR products was digested using restriction endonucleases MspI to identify the genotypes of the CAST gene following the PCR-RFLP technique. Digested products were separated by electrophoresis on 1.5% agarose gel and visualized after staining with ethidium bromide on UV transilluminater. The MspI digestion of the PCR products produced digestion fragments of 306 bp (allele M) and 259 bp (allele N). Genotypic frequency was 75.00, 22.50 and 2.50% for the MM, MN and NN genotypes, respectively. The variation among these frequencies were highly significant. Allele frequency estimates were 0.86 and 0.14 for the M and N alleles, respectively. General qualities of tenderness and acceptability were not affected significantly with different genotypes of the gene. However, the difference in age was highly significantly (P≤0.01) affecting the sensory qualities (flavor, tenderness, juiciness and public acceptance), reaching the highest value for the recipe flavored at age 2-4 years (4.83). The highest value for the mellowness was at age 1-2 years. It amounted 3.18 and showed the highest value of prescription juiciness at age 1-2 years (2.95), while other ages (2-4 years and more than 4 years) were 2.27 and 2.74, respectively. Significant differences (P<0.05) were shown due to age effect for the same muscle; 5.53, 5.34 and 5.24 for the age classes 1-2 years, >4 years and 2-4 years, respectively. The muscle post-mortem pH was not affected by the genotype in either LD or BF muscles, in different age classes. Water—holding capacity was significantly affected by the CAST genotype and showed significant differences (P<0.05). It is therefore concluded that age of animals and CAST genotype can be relied on for selection porposes for meat quality in Awassi sheep.