Submitted to: Journal of Meat Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2007
Publication Date: 10/1/2007
Citation: Bee, G., Pursel, V.G., Mitchell, A.D., Maruyama, K., Wells, K.D., Solomon, M.B., Wall, R.J., Coleman, M.E., Schwartz, R.J. 2007. Carcass composition and skeletal muscle morphology of swine expressing an insulin-like growth factor-I transgene. Archives of Animal Breeding. 50(5):501-519. Interpretive Summary: This study was conducted to further elucidate the impact of insulin-like growth factor I (IGF-I) expression on the carcass characteristics and muscle fiber morphology of the progeny from transgenic founder swine. This research indicates that using a transgene to deliver expression of IGF-I specifically to skeletal muscle was effective for enhancing muscle development and reducing backfat depth in swine killed at 120 kg BW. The magnitude of this improvement in the lean to fat ratio in carcasses was somewhat lower than has previously been reported for pigs administered growth hormone by injections or implants. In this study animal productivity was improved by the transgene without an adverse affect on general animal health. Additional research will be required to determine whether the improvements in carcass composition seen in gilts will also occur in barrows, and whether similar results can be obtained when transgenic pigs are crossed with other genetic backgrounds. Evaluation of pork quality and safety of pork products that contain elevated IGF-I will be required before the potential of this transgene for application to the swine industry can be fully assessed.
Technical Abstract: Research was conducted to determine if directing expression of insulin-like growth factor I (IGF-I) specifically to striated muscle would enhance lean muscle growth in swine. At 120 kg BW 25 transgenic and 26 control pigs were sacrificed to evaluate carcass composition. Transgenic pigs had lower percentages of fat and higher percentages of lean tissues than control pigs for the overall carcass and each carcass region (P less than or greater than 0.002 for each). Expression of the IGF-I transgene did not alter the percentages of the three fiber types in the five skeletal muscles, however, fiber areas of LM and serratus ventralis were larger (P less than or greater than 0.031) in transgenic than in control pigs. In transgenic pigs the relative abundance of IGF-I mRNA in gastrocnemius, gluteus medius, LM, and the average for all five skeletal muscles was positively (P less than or greater than 0.011) correlated with percentage of carcass lean (r = +0.597 to 0.804) and negatively (P less than or greater than 0.048) correlated with average backfat (r = -0.486 to -0.629). Based on these results we conclude that expression of IGF-I specifically in skeletal muscle had a positive effect on carcass composition of swine.