Submitted to: Animal Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2003
Publication Date: 9/1/2003
Citation: Pursel, V.G., Mitchell, A., Bee, G., Elsasser, T.H., McMurtry, J.P., Wall, R.J., Coleman, M.E., Schwartz, R.J. 2004. Growth and tissue accretion rates of swine expressing an insulin-like growth factor 1 transgene. Animal Biotechnology. 15:33-45. Interpretive Summary: Previous research has indicated that exogenously administered insulin-like growth factor I (IGF-I) was either ineffective, or required more frequent or higher dosage to be effective for enhancing growth of swine. In the present research a transgene was used to deliver expression of IGF-I specifically to striated muscle so that it would have the opportunity to act locally to stimulate muscle development. The transgene appeared to be effective for reducing the fat and increasing the lean tissue composition of pigs at 120 kg body weight. However, neither the growth rate nor feed efficiency of the transgenic pigs exceeded that of the sibling control pigs. The magnitude of this change in body composition is considerably less than has previously been reported for pigs administered growth hormone by injections or implants. The transgene did not increase the incidence of health-related problems or the death rate compared to sibling control pigs. .Information on carcass composition, 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: The goal of this research was to determine whether directing expression of an insulin-like growth factor I (IGF-I) transgene specifically to striated muscle would alter the growth characteristics in swine. Transgenic pigs were produced with a fusion gene composed of avian skeletal alpha actin regulatory sequences and the cDNA encoding human IGF-I. Eleven litters of transgenic and sibling control progeny were produced. Daily gain of pigs a they grew from 20 to 120 kg, efficiency of feed utilization, and pig survival did not differ between transgenic and control pigs. Plasma IGF-I and porcine growth hormone concentrations were determined at 60, 90 and 120 kg body weight. Plasma IGF-I concentrations were 19% higher in transgenic gilts than control gilts and 11.1 % higher in transgenic boars than control boars (P = 0.0005). Plasma IGF-I concentrations for boars were also higher than for gilts (P = 0.0001). At 60, 90 and 120 kg body weight each pig was sscanned by dual energy x-ray absorptiometry (DXA) to derive comparative estimates of carcass fat, lean, bone content of the live animal. Control pigs had more fat and less lean tissue than transgenic pigs at each of the scanning periods, and the difference became more pronounced as the pigs grew heavier (P < 0.005 at each weight). Transgenic pigs also had a slightly lower percentage of bone than control pigs (P < 0.05 at each weight). While daily rates of lean tissue accretion did not differ for transgenic and control pigs, daily rates of fat accretion were lower in transgenic pigs than in control pigs (P < 0.05). Based on these results we conclude that expression of IGF-I in the skeletal muscles gradually altered body composition as pigs became older but did not have a major affect on growth performance.