ABSTRACT
Early transgenic farm animal research was inspired by the dramatic growth of transgenic mice that expressed a growth hormone (GH) transgene.[1] A number of transgenic pigs and sheep were subsequently produced with human, bovine, rat, porcine, or ovine GH under the control of several gene promoters.[2] Although pigs expressing GH transgenes grew faster, utilized feed more efficiently, and were much leaner than their nontransgenic siblings, they were not larger and exhibited several notable health problems, which included lameness, susceptibility to stress, gastric ulcers, and reproductive problems.[2] The GH transgenic lambs did not grow faster or utilize feed more efficiently than control lambs, but they were much leaner and had serious health problems.[2]
More recently, an insulin-like growth factor-I (IGF-I) transgene has been used to produce transgenic pigs with enhanced muscle development and reduced fat in the carcass, but the transgene did not improve growth rate or feed efficiency. In contrast to the GH transgenic pigs, definitive phenotypes for the IGF-I transgenic pigs were not detected, and no gross abnormalities, pathologies, or health-related problems were encountered.[3]
MODIFICATION OF MILK COMPOSITION
Transfer of genes to alter milk composition has thus far received little research emphasis, but offers the dairy industry considerable potential for the future. A list of potential changes in milk components worthy of consideration is shown in Table 1.
