Genetic models of human disease can lead to new insights concerning di
sease aetiology or suggest novel therapeutic interventions. Livestock
species, especially pigs, cows, sheep and horses, ate often good anima
l models of human disease. However, genetic models in livestock specie
s have included only the study of spontaneous mutations. Production of
transgenic livestock is now possible but owing to a low efficiency of
production, it is very expensive and its application limited. Anticip
ated application of improved technologies such as embryonic stem cells
and homologous recombination will allow for increased sophistication
of experimental design and wider use of genetically modified livestock
. In all cases, the appropriate species for a genetic model of human d
isease should be the species which best models the physiology of the o
rgan or system under consideration. In the future, livestock will play
an increasingly more important role in biomedical research through th
e application of genetic engineering methodologies.