**2. The importance of animal models in the study of CLD**

Throughout history, experimental animals have played a key role in the research of diseases affecting human beings. Rodents are similar to humans in their anatomical, physiological, genetic, molecular, and biochemical conditions, which facilitates studies involving certain diseases. They also incorporate complex factors, such as the environmental and background genetic and molecular changes within a cell under pathological conditions, making them an ideal research tool. From the perspective of scientific research, animal experimentation has contributed considerably to the growth of biomedical science, from the development of prophylactic measures and methods of diagnosis to disease treatments for humans [21, 22]. It can additionally provide information on mechanisms of injury, drug target identification, and characterization of the pharmacological and toxicological profile of innovative drug development.

The best animal model must be easily performed in the laboratory, be reproducible, have no features unrelated to the disease, have minimal limitations, and, most importantly, reproduce both the histopathological and clinical characteristics of the human disease. Poor or inadequate models will result in limited or erroneous information, perhaps even data that cannot be extrapolated to humans. The choice of an experimental model must be precise, as it is the most essential piece in the experimental strategy for the study of liver disease. The most pertinent animal models for CLD research are rodents (rats, mice, and hamsters), but rabbits have been used as well [23]. These animals meet all the basic conditions needed to induce, manipulate, and obtain biological samples for the study of liver disease. Although the choice of the appropriate animal model appears easy, one must take into consideration that it will not completely mimic the human disease because each patient has different and diverse clinical signs and symptoms, comorbidities, genetics, and the complications that might occur from the disease. These conditions cannot be identically mimicked in experimental animals, but it is possible to reproduce the histopathological and functional alterations occurring in the liver tissue. Therefore, the success of CLD studies in animals will depend on the choice of an experimental model that can represent those changes in the liver. Generally, CLD study involves experimentally inducing the disease in the animals, either *via* chemical agents, surgery, genetic modifications, or diet [24]. If the research, however, is focused on mechanisms of injury, specific pathophysiological processes of the disease, molecular targets, pharmacokinetics, or pharmacodynamics, it is important to accurately select species, gender, age, size, number of animals, etc. Said choice will depend on the desired number of samples, organ size, blood volume for the quantification of biochemical parameters and liver enzymes, or obtaining DNA, RNA, etc., for molecular studies. An appropriate experimental animal model enables understanding of the disease, including identification and stage differentiation.
