The present paper describes spontaneous pathological findings including etiological aspects in digestive tracts of kangaroos, which have been detected in 166 necropsies during the last 20 years. Protozoan - infections, herpes virus infections, gastroenteritis of unknown etiology and especially the occurrence of the so called "lumpy-jaw" turned out to be of special importance. These findings are discussed with reference to the literature, completed as well by short literature reviews, sub-divided into the different organs and the variable etiology of the diseases, as by a brief description of digestive tract physiology and anatomy in marsupials.

The study of animal welfare continues to struggle with two persistent, interrelated problems: how to define animal welfare, and how to determine which measures should be used to evaluate it. One potential indicator of an animal’s welfare is the presence or absence of stress, or anything that seriously threatens homeostasis. The actual or perceived threat to an organism, the stressor, and the response will determine when stress becomes distress. Pathologically speaking, this occurs when tissue damage (lesions) and disease appears as a result of a severe (acute) or prolonged (chronic) stress response. Veterinary Pathology is a diagnostic tool, which looks for and identifies lesions involved in disease/s as well as determines cause/s of death. In this respect Veterinary Pathology could be a diagnostic tool of cetaceans’ (whales, dolphins and porpoises) welfare. In recent years, attention has been focused on how human activities may affect cetaceans, particularly through use of improving methods and techniques to identify and classify lesions, and to understand mechanisms and causes, in order to associate stressors with distress. In this chapter we discuss three test cases (beaked whales mass stranding and antisubmarine mid-frequency active sonar, active stranding and capture myopathy, fingerprints in the brain of dolphins). We show what animal pathology can do to contribute to animal welfare assessment in stranded cetaceans, ranging from death to improved population welfare.