Described herein are rats with a hepatic deficiency comprising decreased function, activity, or expression of an enzyme in the tyrosine catabolic pathway (such as fumarylacetoacetate hydrolase), and methods of using the same for in vivo engraftment and expansion of heterologous hepatocytes, such as human hepatocytes, analysis of human liver disease, and analysis of xenobiotics. Also disclosed is the use of immunodeficient rats for the engraftment and expansion of heterologous hepatocytes.
