Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/1997
Publication Date: N/A
Citation: Interpretive Summary: Previous transgenic animal research has shown that expression of growth hormone (GH) transgenes in swine can enhance growth rate, increase efficiency of feed utilization, and dramatically reduce carcass fat content. However, rigorous regulation of the transgene expression is needed so that the animals are only exposed to elevated GH for about two months. The present experiment was conducted with a sheep GH transgene that when tested in mice only provided a low level of transgene expression unless the mice received zinc supplementation. Of the 12 transgenic pigs that were evaluated, five exhibited very high levels of GH, one exhibited low levels of GH and six did not have elevated GH. When that latter seven transgenic pigs received supplemental zinc in their feed, the pig with a low level of GH responded with a 20-fold increase in the level of GH, and the other six pigs remained unresponsive. Thus, while transgene was quite inducible by zinc in pigs, the background level of transgene expression was too high for this transgene to be effective for use in swine production.
Technical Abstract: An ovine metallothionein-1a (oMT1a)-ovine growth hormone (oGH) fusion gene was microinjected into 400 pig zygotes to produce 15 transgenic pigs. Five pigs expressed high levels of oGH, one pig expressed low levels of oGH, and six did not have constitutive oGH expression. Dietary supplementation with 2,000 ppm zinc for 6 d induced a 20-fold increase in plasma oGH in the pig with low GH expression but did not induce expression in the other six pigs. The average daily gain of five transgenic pigs with elevated oGh was 5% higher than littermate controls during a 9-wk feeding trial. The liver, kidney, adrenal and thryoid weights were all significantly heavier for the oGh-expressing transgenic pigs than for non-transgenic littermates. Total carcass fat, longissimus muscle fat, subcutaneous back fat thickness and loin eye area were lower, and carcass protein and water content and longissimus muscle B Red fiber area were higher in the transgenic pigs with elevated oGH than in littermate controls. (P <.05 for each). The data indicate that while the oMT1a promoter was more inducible by zinc in swine that was previously reported for the mouse MT promoter, the former provided a higher level of constitutive expression than the mouse MT promoter.