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As part of the Harwell Ageing programme, experimental cohorts of mice are being aged to 18 months. Mice have their weight recorded at regular intervals and we have found this information can also be a valuable indicator for welfare concerns.

It is important to know what the weight of an individual is being compared to, for example some animals may appear leaner than others. It is essential to know what is 'healthy' for the individual animal by assessing the animal's while weight history and using information known from the background strain.

Assessing animals over 1 year of age, by using body condition checks, palpating for growths in the abdomen and recording weight every 6 weeks, has helped us to pick up possible welfare concerns. Tumours in the abdomen can be easily felt for by gently palpating and is usually coupled with a deterioration of body condition and weight loss.

At Harwell, animals within experimental cohorts that show signs of weight loss are monitored at more regular intervals. Individuals that have lost 8-14% weight are weighed weekly if their overall body condition appears fine and there is no sign of a growth developing in their abdomen. From our studies, weight loss was taken from the maximum weight the animal reached.

Examples of background strain weight data