Reduction

Probably the two main means by which fewer animals can be used in an experiment relate to the design of the experiment and the way its progress is monitored.

Imaging helps to reduce animal numbers [Corbis].

Greater emphasis is now being placed on designing experiments so they use the right number of animals - not too many, not too few. Modern statistical methods mean that scientists can have more confidence that using lower numbers will still generate valid information. It has been suggested that there is the scope to reduce the numbers of animals needed in basic research by up to 25% through applying best statistical practice.

Monitoring the progress of an animal experiment would often require that some of animals were put down at each stage so that a post mortem could be carried out. The animals' vital organs would be examined under the microscope - that was the only way to see how a disease was progressing or whether a medicine was having an effect. Today, imaging technology means that often an animal does not need to be put down but can be examined repeatedly - it acts as its own control. For example, using MRI scanning has meant that only 24 rats were needed in an asthma study that previously would have demanded 500.

A different aspect of reduction comes with the breeding of transgenic animals. Transgenics - mice in particular - have had their genetic make up altered. This helps scientists work out what a particular gene linked to a disease is doing or means the mouse can mimic human disease more accurately. One quarter (710,000) of all the animal procedures reported in 2002 were with genetically modified animals, and the proportion is growing.

Research programmes involving transgenic mice can, like any other research programme, stop and re-start. Research establishments do not wish to continue breeding unneeded mice so increasingly they are freezing the embryos and sperm of transgenics. This cryopreservation means if a particular transgenic is indeed needed again, there have been no unwanted animals during the gap. Also there will be no need to start the breeding programme right from the start. This again saves lives as breeding of transgenics takes several generations before the desired animals are obtained. Another animal welfare benefit is that frozen embryos and sperm can be shipped to other laboratories in the UK or overseas, thus avoiding any distress of the journey to live animals.

Another breeding strategy, that also reduces numbers, involves identifying the sperm destined to produce females from the sperm destined to produce males. Sperm for female rats contains more DNA than sperm for male rats. Fluorescent dye is added to sperm and a laser sorts the brighter sperm (female) from the duller sperm (male). This is useful because some experiment require one sex only.