Production and analysis of transgenic pigs containing a metallothionein porcine growth hormone gene construct

While initial studies with growth hormone (GH) fusion genes demonstrated th at transgenesis could be used to enhance growth performance in the pig, the y also highlighted the need to be able to control expression in order to av oid pathological problems associated with high-level expression. We have pr oduced transgenic pigs containing a GH construct consisting of a modified h uman metallothionein IIA (MT) promoter fused to the cDNA sequence for the p orcine growth hormone gene. A total of 289 pigs were born live of which 88 (2.8% of embryos injected) were transgenic. Founders were reared on diets c ontaining 100 ppm of zinc. Induction of transgene expression was assessed b y feeding 1000 ppm of zinc in the diet (high zinc) for 3 weeks and measurin g plasma IGF-I as a marker of CH production, before, during and after the h igh zinc. diet. Evidence to suggest that transgene expression could be indu ced was obtained in 12/36 founders tested. Founders were mated to nontransg enic animals to produce transgenic progeny. Twenty-two per cent (4/18) of m ale founders did not transmit the transgene and 39% (7/18) transmitted the transgene at frequencies of less than 30%. The effect of transgene expressi on on growth performance was evaluated by feeding transgenic and non-transg enic progeny the high zinc diet from 20-100 kg liveweight. Rate of gain, fe ed intake and estimates of carcass fat and muscle were compared between the two groups of progeny of 60-100 kg liveweight. Analysis of transgenic prog eny growth performance was confounded by considerable individual variation between transgenic progeny and the relatively few transgenics available for evaluation from mosaic founders. A number of transgenic progeny exhibited enhanced growth performance and have been selected for further breeding and analysis.