Answer from Chris Bowden, International Species Recovery Officer & Saving Asia’s Vultures from Extinction (SAVE) Programme Manager:
Unfortunately, diclofenac remains potent to vultures for as long as it is in the tissues. A treated cow has very high levels of diclofenac in its tissues (especially in kidneys, liver, visceral organs as well as muscle tissues) for at least 3 days after treatment, after which it gradually reduces so that a week after treatment it is probably at safe levels if the cow lives that long (the diclofenac is mainly excreted in urine and passes through its system in that time) … BUT – unfortunately… if the cow dies within those 3-4 days after diclofenac treatment, then the diclofenac simply remains in the tissues and the meat is highly toxic to the vultures for a very long time indeed.
So in simple terms, keeping the meat of a treated cow before feeding it to vultures does not make it any safer at all… hence unless you really know whether it was treated or not, it should not be given to them.
This is a very important point to be clear on, especially for any prospective vulture feeding stations, and means it is a major added challenge to be 100% sure that livestock have not been treated in the week or so before their death.