Types of humane endpoints

Generally, humane endpoints can be based on different categorizing indicators like: 

• clinical signs (e.g.: tumor formation);
• pathophysiological changes (e.g. drop in body temperature);
• behavioural changes (e.g.: stereotypic behaviour);
• biochemical changes (e.g. ketonury);
• hormonal changes (e.g. prolactin). ​

New Developments in the field of humane endpoints

New developments in the field of humane endpoints focus on achieving maximal reduction of pain and/or distress and, if possible, to eliminate them completely. Generally speaking, the developments can be grouped into one of two categories:

Preclinical humane endpoints

Preclinical humane endpoints are endpoints that can be identified before the onset of pain or distress.

By way of example: think of the use of non-invasive measuring technologies such as bioluminescence. This molecular biology technique involves labeling of virulent micro-organisms or tumor cells with the luciferase gene. The labeled pathogen or tumor cell can then be followed in a non-invasive manner. This technology can be used to gauge the growth or dissemination of the pathogen or the tumor cell (e.g. in metastatic disease), so that the animal can be removed from the experiment at an early stage, even before clinical signs become manifest.

Another example of a preclinical endpoint may be found in the use of molecular biology techniques such as transcriptomics (expression profiling). This means that in carcinogenicity studies, the endpoint may be the up or down-regulation of the genes associated with tumor growth, rather than the appearance of the tumor itself.

Non-clinical humane endpoints

With non-clinical humane endpoints, the procedure in the experiment that will ultimately lead to clinical signs is replaced by a procedure that will not result in clinical signs. A clear example is to be seen in the efficacy study for a newly-produced batch of vaccine. Until recently, this type of study to determine the degree of protection afforded by a vaccine required challenging vaccinated animals several weeks post immunization with an injection of the virulent micro-organism (or its toxin). The degree to which the animals were protected was taken as the measure of efficacy of the vaccine.

Nowadays, for several types of vaccines, the illness-inducing challenge procedure may be replaced with a blood test in which the degree of protection is determined by in-vitro antibody titration (i.e. by demonstrating pathogen or toxin neutralization in tissue culture or in an ELISA assay).