Argument: Genetically modified animals often contract genetic diseases
"Genetically Modified Animals in Research". Fund for the Replacement of Animals in Experimentation - "The demand for better animal models for drug development and toxicity testing, and the need to define the roles of specific human genes have resulted in a worldwide increase in the generation and use of genetically modified animals.
In 2005, 957,451 procedures were performed on genetically modified animals and recorded within that year's UK Home Office statistics. Another 288,101 animals used in scientific procedures that year carried harmful genetic defects that had dramatic consequences for their welfare. By far the most commonly used laboratory species for these procedures was the mouse."