Since large animal transgenesis has been successfully attempted for the first 
time about 25 years ago, the technology has been applied in various lines of 
transgenic pigs. Nevertheless one of the concerns with the technology--animal 
welfare--has not been approached through systematic assessment and statements 
regarding the welfare of transgenic pigs have been based on anecdotal 
observations during early stages of transgenic programs. The main aim of the 
present study was therefore to perform an extensive welfare assessment comparing 
heterozygous transgenic animals expressing GFP with wildtype animals along 
various stages of post natal development. The protocol used covered reproductory 
performance and behaviour in GFP and wildtype sows and general health and 
development, social behaviour, exploratory behaviour and emotionality in GFP and 
wildtype littermates from birth until an age of roughly 4 months. The absence of 
significant differences between GFP and wildtype animals in the parameters 
observed suggests that the transgenic animals in question are unlikely to suffer 
from deleterious effects of transgene expression on their welfare and thus 
support existing anecdotal observations of pigs expressing GFP as healthy. 
Although the results are not surprising in the light of previous experience, 
they give a more solid fundament to the evaluation of GFP expression as being 
relatively non-invasive in pigs. The present study may furthermore serve as 
starting point for researchers aiming at a systematic characterization of 
welfare relevant effects in the line of transgenic pigs they are working with.