Right Livelihood and Veterinarians

I went to the vet last weekend and it got me thinking- veterinarians often kill animals in order to relieve suffering; would this form of killing be considered to violate the first precept, even though it would be done out of compassion? If so, would a career in vet medicine not be considered right livelihood? It seems as though leaving animals instead to die a slow and painful death would be inhumane. Just curious, thanks for reading. Ian Found this interesting article via a similar question, if anyone is still interested: http://www.urbandharma.org/pdf/geth0401.pdf