INSERTION OF GROWTH HORMONE GENES INTO PIG EMBRYOS

Abstract

Recent research has clearly demonstrated that genes coding for growth hormone (GH) and growth hormone releasing factor (GRF) can be integrated into the genome of domestic swine by microinjection of the cloned genes into a pronucleus or nucleus of fertilized pig ova. The percentage of injected ova that developed into transgenic pigs varied from 0.30% to 1.69%. The proportion of transgenic pigs that expressed the gene varied from 17% to 100%. depending upon the composition of the fusion gene. The elevation of foreign GH in expressing transgenics stimulated the expected elevation in insulin-like growth factor (IGF-I). Enhanced growth rate has been reported for some transgenic GH pigs but not for others, with the difference possibly due primarily to dietary constraints and general health of the pigs. Expression of the GH genes has markedly reduced subcutaneous fat and improved the efficiency of converting feed into meat. The persistent excess GH in transgenic pigs was detrimental to general health; lameness, lethargy, and gastric ulcers were the most prevalent problems. Females that expressed foreign GH genes were anestrus. Most of the transgenic pigs that were reproductively sound transmitted the gene to a portion of their progeny.