Water balance in the dog and cat

In respect of its metabolic control of water balance, the cat probably differs as much from the dog as it does in most other respects. In qualitative terms the routes of gain and loss of water are very much the same: in quantitative terms and in its homeostatic response to different environmental stimuli or insults the cat and the dog are rather different. Dogs and cats are among the commonest species with which veterinarians have to deal. They share much the same environment and are treated in much the same way by their owners. They are almost interchangeable as pets. So far as the veterinary profession is concerned, there are a few outstanding differences such as their response to certain drugs, their reproductive behaviour and their range of aggressive and defensive weapons—but they are in other ways treated in a somewhat similar fashion. It is, however, only within recent years that some other outstanding differences have really become identified between the two species. These differences are in aspects of protein, fat and vitamin metabolism which have direct or indirect relevance to feeding cats and dogs. But they are also manifest in water metabolism, which is the subject of this paper. The first part of this paper will deal with some differences in the water metabolism of dogs and cats which are in the scientific literature but are not widely known outside the research field. The second part will describe some of the work which we have been doing on food/water interrelationships of the dog and cat.