What about vaccinations?
"As to the use of vaccines and other substances that may in some way involve the use of blood in their preparation, it should not be concluded that the Watch Tower Society endorses these and says that the practice is right and proper. However, vaccination is a virtually unavoidable practice in many segments of modern society, and the Christian may find some comfort under the circumstances in the fact that this use is not in actuality a feeding or nourishing process." (The Watchtower, November 1, 1961, page 670)
So injecting is not "feeding or nourishing"?
In the case of snake anti-venene, a horse has several litres of blood taken at a time.
Doug