Alteration of carcass composition in transgenic swine

Abstract

During the past decade, scientists have learned how to transfer re‐combinant genes into the genomes of livestock to produce “trans‐genic” animals. Microinjection of ova with copies of a gene is the primary method used, but the efficiency is low. About 1% of injected ova result in transgenic offspring. Initial research primarily involved genes encoded for growth hormone (GH). The GH transgenes that have thus far been used result in high concentrations of GH being produced throughout life. In general, GH (bovine) pigs did not grow larger than their sibs, but they gained weight up to 13% faster and they were 18% more efficient in utilizing feed. The excess GH dramatically altered carcass composition in comparison to sibs. At 92 kg, carcasses of GH pigs had 85% less total fat, which consisted of 85% less saturated fatty acids (SFA), 91% less monounsaturated fatty acids (MUFA), and 66% less polyunsaturated fatty acids (PUFA) than sibs. In primal cuts of GH pigs, intramuscular fat was reduced 43% in ham, 66% in loin, 64% in shoulder, and 69% in belly. No significant differences were detected in meat tenderness (shear force) for GH transgenics and sibs. Persistent excess GH in transgenic pigs was detrimental to their health. These problems were of such magnitude that these pigs could not be used for farming. When molecular biologists know more about gene regulation, transgenes can be constructed in which GH secretion might be tightly regulated. At that time, transgenic swine may be produced with positive attributes provided by a GH transgene, or other transgenes, with potential to improve carcass merit without adversely altering the health status of transgenic swine.