Carcass composition and skeletal muscle morphology of swine expressing an insulin-like growth factor I transgene

Abstract. Research was conducted to determine if directing expression of insulin-like growth factor I (IGF1) specifically to striated muscle would enhance lean muscle growth in swine. At 120 kg BW, 25 transgenic (T) and 26 control (C) pigs were sacrificed to evaluate carcass composition. T-pigs had lower percentages of fat and higher percentages of lean tissues than C-pigs for the overall carcass and each carcass region (P ≤ 0.002 for each). Expression of the IGF1 transgene did not alter the percentages of the three fiber types in the five skeletal muscles, however, fiber areas of longissimus dorsi muscle (LM) and serratus ventralis were larger (P ≤ 0.031) in T- than in C-pigs. In Tpigs the relative abundance of IGF1 mRNA in gastrocnemius, gluteus medius, LM, and the average for all five skeletal muscles (ASM) was positively (P ≤ 0.011) correlated with percentage of carcass lean (r = +0.597 to 0.804), whereas the relative abundance of IGF1 mRNA in the LM and the ASM was negatively (P ≤ 0.047) correlated with average backfat (r = −0.546 and −0.488, respectively). Based on these results we conclude that expression of IGF1 specifically in skeletal muscle had a positive effect on carcass composition of swine.