Transfer of an ovine metallothionein-ovine growth hormone fusion gene into swine.

An ovine metallothionein-1a (oMT1a)-ovine growth hormone (oGH) fusion gene was microinjected into 400 pig zygotes, the zygotes were transferred into recipient females, and 15 founder transgenic pigs were born. Of 12 transgenic pigs assayed, five expressed high levels of oGH (> 900 ng/mL plasma), one expressed low levels of oGH (10 to 30 ng/mL), and six did not express oGH. Dietary supplementation with 2,000 ppm of zinc for 6 d induced a 20-fold increase in plasma oGH in the transgenic pig with low expression but did not induce expression in the six transgenic pigs with no constitutive oGH expression. The average daily gain of five transgenic pigs with elevated oGH was similar to that of non-transgenic littermates during a 9-wk feeding trial (P = .52). The liver, kidney, adrenal, and thyroid weights were all significantly heavier for the oGH-expressing transgenic pigs than for non-transgenic littermates. Total carcass fat, longissimus muscle fat, subcutaneous backfat thickness, and loin eye area were lower and carcass protein and water content and beta R fiber area of longissimus muscle were higher in the transgenic pigs with elevated oGH than in their littermate controls (P < .05 for each). The data indicate that even though the oMT1a promoter was more inducible by zinc than was previously reported for the mouse MT promoter in swine, the former provided a higher level of oGH expression than the mouse MT promoter.