Expounding on Satanus' reference to WT excuses note the original QFR in 1964:
*** w64 2/15 pp. 127-128 Questions from Readers ***
Would it be a violation of the Scriptures for a Christian to permit a veterinarian to give blood transfusions to a pet? And what of animal food? May it be used if there is reason to believe there is blood in it? Also, is it permissible to use fertilizer that has blood in it?
What, then, of animal food? May it be used if there is reason to believe there is blood in it? As far as a Christian is concerned, the answer is No, on the basis of principles already mentioned. Therefore, if a Christian discovers that blood components are listed on the label of a container of dog food or some other animal food, he could not conscientiously feed that product to any animal over which he has jurisdiction. He could not conclude that doing so would be excusable, for this would not be a case of an animal killing another animal and helping itself to the blood of that creature. (?????) No, this would be a direct act on the part of the Christian, making him responsible for feeding blood to a pet or other animal belonging to him.
Of course, if there is no indication on the label of a package of animal food that the product contains blood, a Christian might conclude that it could be used. Still, his conscience might trouble him. In that case he should put his conscience to rest by making reasonable inquiry and acting in accord with the information he receives, for a Christian surely desires to have a good conscience before God.?1 Pet. 3:21.
But now, what about fertilizer that has blood in it? One who is going to show respect for God?s law on blood would not use it. True, according to the Mosaic law, blood when taken from a body was to be poured out upon the ground and covered over with dust. (Lev. 17:13, 14) The objective was, however, that the blood should serve no useful purpose when thus disposed of. It was not placed on the ground with the thought in mind that it would serve as fertilizer. Hence, no Christian farmer today could properly spread blood on his fields to fertilize the soil, nor would he use commercial fertilizer containing blood. Such blood use would be a commercializing on something that God has reserved for himself. It would be a violation of God?s Word.
Ah, the old dogmatic days... Now the WTS answers questions with questions:
*** w81 10/15 pp. 30-31 Questions from Readers ***
Another situation that sometimes arises involves feeding blood to animals. It is true that at present many animals in the wild do not live on vegetation as the Bible says they did originally. (Gen. 1:30) Rather, they eat other creatures, blood and all. Nonetheless, would a Christian who knows God?s law on blood intentionally feed blood to animals under his care? Would that harmonize with what he knows about how blood was handled under the Law?
And now we note the logical gynastics of leeches and blood:
*** w82 6/15 p. 31 Questions from Readers ***
However, though leeches parasitically feed on blood in their natural state at present, it would not be proper for a Christian to permit leeches to draw his blood. (Proverbs 30:15) Even where this was urged for medical reasons and the leeches would later be disposed of, the use of leeches would involve deliberately feeding blood to these creatures. That would conflict with the Bible?s indication that blood, being sacred and representing life, should be disposed of if it is removed from a body.
HAHAHAHAHAHAHAHAHA!!!! Right (as I gain my composure), so even though God didn't create animals to eat blood originally (including leeches it seems ) they do now with God's sanction, but we don't want to d elirberately feed them blood. OK. Finally the next quote makes perfect sense...
*** w05 1/15 p. 20 Foregleams of God's Kingdom Become a Reality ***
Perhaps some have found certain information published by "the faithful and discreet slave" hard to grasp.