Generally speaking, animal trial work falls into two main categories. There is the work that involves the use of anima as test models for products. In this case the animals are being used to test the safety and effectiveness of new substances to avoid putting human subjects to any risk. There is also the work that involves the use of animals as test models for therapeutic substances designed for animal use (veterinary products). In this case the animal subjects are performing a function similar to that of human subjects in a clinical trial, the main difference being that it is not voluntary.

Consider the first category animal models for testing the safety and effectiveness of new substances. The types of animals in common use for this purpose include mice, rats, guinea pigs, ordinary pigs, and rabbits. Several reasons influence the choice of animal models for trial work, including cost of purchase and maintenance, applicability for the type of trial work involved and the mechanisms of specific physiological functions peculiar to the species. In the main, mice, rats and guinea pigs are probably the most universally used animals. Pigs are valuable test models for substances involved with gastric changes due to the similarity of the gastric system in pigs and human beings.

In trial work involving animals, the problem of subjectivity can usually be ignored. Animals cannot be expected to have an emotional response and should not have a psychological response to trial stimuli. Stress factors cannot be ignored, however, and in fact animals can be used to demonstrate stress influences on body reactions.

Trials in which the effects of stress, in conjunction with drug treatment, on gastric ulceration in rats and pigs have been carried out. These have shown that stress does have an adverse influence on the degree of ulceration created by a particular drug. It is of interest to note that a stress condition in animals can be induced by subjecting the animals to physical factors such as cold, heat or restraint. Think of the analogy here with humans subjected to climatic extremes or physical restraint, for instance, physical incapacity or enforced change of home surroundings. Thus, any trial work done on animal models should take account of the fact that they are subject to stress factors and that these may not be as apparent as they would be in human subjects.

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