This idea must begin with the realization that Christ's redemptive work was for all creation. John 3:16- God so loved "the world." God loved the cosmos- the entire universe, not just the human world. Again in II Corinthians 5:19, God reconciled the cosmos to himself in Christ. Certainly this does not deny the spiritual dimension of humanness which can commune with The Spirit, but it does make verses such as Romans 8:19, 20 more understandable.
In Romans we are told that "the creation waits in eager expectation for the sons of God [note small s on "sons"] to be revealed... that creation itself will be brought into the glorious freedom of the children of God." The main theme in these verses refers, of course, to the future time when death and decay will cease. The curse of the fall will be banished. However Christianity is, in its essence, a way of life which requires change now in the direction of the perfection which will only be realized when Christ returns. We accept this preposition easily in terms of our moral behavior when we aim to become (by God's grace) more loving, giving, etc. But there is a large corollary of thought (too big to tackle fully here) which relates this to all creation. Francis Schaeffer says, "Christianity... has in it the possibility of substantial healings now in every area where there are divisions because of the fall... The Christian who believes the Bible should be... [one] who is treating nature now in the direction of the way nature will be then." (Pollution and the Death of Man, p 68,69)
How will nature be "then?" No carnivores. (what implications here for ecology before the Fall and after the Second Coming!) Isaiah 11:7 and 65:25. The lion will eat grass like the ox, and food chain subordinates will become peers.
The next point to ponder is the origin of animal deaths. God initiated the slaughter! He killed animals for their skins to cover the naked and aware Adam and Eve. (Genesis 3:21) This was the first animal sacrifice, an integral part and huge burden of the curse. We then begin to see the salvation of creation unfold, intertwined with the familiar story of human redemption. The quintessential Old Testament picture of redemption, the Passover, had redemptive adequacy for beasts as well as humans. The firstborn of the Egyptians' livestock, as well as of their families died on that fateful night. But the passover blood on the Hebrew's doors protected their flocks as well as their children. (Exodus 11, 12, 13)
Continuing to think about redemption being provided by sacrifice, we are brought smack up, hard, against the immutable truth of I Peter 3:18: "Christ died for sins once for all." And also, in Hebrews 9:22, 26: "Without the shedding of blood there is no forgiveness... but now he [Christ] has appeared once for all at the end of the ages to do away with sin by the sacrifice of himself." The blood of Christ replaces and supercedes the blood of animals. The blood of Christ covers all sin.
I do not think it is too big of a step to choose to participate in the redemptive work of Christ by extending the forgiveness of God to the animal kingdom now. I can aim to treat all of creation as it will be in perfection- no sin or death, waste or decay. I can move in the direction of godliness in all aspects of my life. Does this mean that I have become a strict vegetarian? Well, no; no more than it means that I am perfectly loving or forgiving. (And if you think I have those traits perfected you don't know me very well, ha ha.) Remember I call this section "Off the Wall."
But I do often find myself asking, "Since the Creator has already given His perfect sacrifice, how many more creatures must die for me?"