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Blood clotting is the incredible process that keeps deer on their feet when injured or even mortally wounded. Here’s how it works.

By Dr. Phillip Bishop

Last fall I was bowhunting with one of my favorite buddies in a beautiful timber tract surrounded by suburbia. The place was full of deer sign, and he put me in one of his best stands. I hadnxe2x80x99t been there long when deer started appearing xe2x80x94 including a very nice buck, easing along the far end of a small greenfield. It didnxe2x80x99t take me long to make the decision that I would shoot as soon as he stepped clear of the thick brush, but he turned just before I had a clear shot. I didnxe2x80x99t have too long to grieve, though, because another deer stepped out into the open field from the opposite direction. But in this case, it didnxe2x80x99t take me long to decide not to shoot. It was clearly a young deer, and since it was alone, was likely a buck.

A little while later, a young doe showed up, which I first assumed was a young buck. But after watching it a while a close range, a careful study of its head and rear made it clear it was a doe. The nature of the area suggested the need to thin the herd, and I hadnxe2x80x99t killed a deer the previous season, partly due to moving to another state. So I drew and released an arrow aimed at the deerxe2x80x99s spine xe2x80x94 the first spine-shot I had taken with an arrow.

The three deer I killed during the 2017 season all dropped in their tracks, including the archery kill, and thatxe2x80x99s why I like the spine shot xe2x80x94 because I have tremendous respect for the excellent ability of deer blood to clot. Let me explain.

The Good and Bad News of Blood Clotting

I consider myself very blessed in that I have lost very few of the deer I have shot in more than 50 years of hunting. The few I failed to recover I attribute to the excellent clotting capacity of deer blood. When you initially find blood, and then it disappears, in most cases clotting is the reason.

When I taught physiology and discussed blood and circulation in class, I told my students that they were potentially within about six minutes of being dead. If our blood spontaneously clots, we are goners. If our larger blood vessels create a clot, and that clot (called a thromboembolus) travels and lodges to block a large artery supplying blood to a large portion of our lungs, brain or heart, we will be dead within a few minutes.

I also told the students that if our blood fails to clot and we hemorrhage (bleed), we might live a little longer than with a clot blocking a major artery, but not too much longer. So the point is that our circulatory system, and that of a deerxe2x80x99s, depends on blood not clotting when we donxe2x80x99t need clotting (within our vascular system) and clotting when we actually do need it (that is, when we are losing blood).

So when a bullet or broadhead damages a deerxe2x80x99s heart or major blood vessels and no clotting occurs, it will bleed out fairly quickly. Blood volume inside the circulatory system gets low enough that blood pressure falls too low for blood to reach the brain and death ensues. This can be observed when an arrowed deer runs for a bit and then stops and gets woozy before toppling over.

On the other hand, if damage to blood vessels is not too severe, the well-designed clotting mechanism effectively stops the leaking blood and the animal escapes and might recover. And in my early academic training, I learned that four-legged animals are able to survive much, much larger blood losses than we humans.

How Clotting Works

It takes about 13 different blood factors coming together to cause blood to clot. In a previous article, (D&DH December 2017) I described the crucial role of Vitamin K in blood clotting. In fact, when an animal is accidentally poisoned with an anti-coagulant such as rat poison, one of the medical treatments is to give it large doses of Vitamin K.

So, one key factor is Vitamin K. Another is Factor 1, which is a protein that is converted in clotting to fibrin, which forms a mesh in the circulation system to start building a clot. Another factor similarly helps form thrombin, which in turn helps produce more fibrin.

Calcium is also a necessary ingredient, along with other substances in blood plasma, which produce a sealing material sufficient to totally stop the flow of blood from the damaged vessels. Several of these factors, when missing, cause different forms of hemophilia (a health condition wherein blood fails to clot).

Effective blood clotting requires proper functioning of the blood vessel walls, platelets and the coagulation proteins. The platelets circulating in the blood respond to damage to the inside wall of a blood vessel, due to a bullet, an arrow, or a predatorxe2x80x99s teeth and claws. They are tiny, but they clump together to aid in forming a clot. In healthy deer, there has to be a fine balance between the drive to form clots and the drive to keep them from forming; and, as I said before, that balance keeps both us and deer alive. That all of these things come together in such an effective way is a tribute to Godxe2x80x99s excellent design.

Harvesting Deer

For us to humanely harvest a deer, our primary goal is to either anchor it on the spot with a major shock to its nervous system (spine shot), or create so much damage to large blood vessels that the clotting mechanism is insufficient to stop blood loss. If you feel confident, and a good shot presents itself, take the spine-shot. Otherwise, target areas that will cause major blood loss. The goal is to do major damage to the heart, lungs or a major blood vessel, and prolong bleeding long enough to render the deer unconscious and ultimately dead. This will also provide a good blood trail, so the deer is easier to recover.

The heart and lungs xe2x80x94 both full of blood xe2x80x94 are obvious targets, and a large, well-designed bullet, delivering adequate terminal energy, is the right tool. An archery kill requires a large and very sharp broadhead. Remember that damage to the blood vessel wall initiates blood clotting, so you want to cut the vessel but damage it as little as possible. A sharp broadhead helps achieve that goal.

Deer have large femoral arteries running up both of their back legs. If severed, they can result in sufficient blood loss to kill a deer. However, there are obvious reasons to avoid this shot due to the ethics associated with a smaller target (vs. broadside heart-lung shots) and the potential to damage a considerable portion of the meat.

So, hit the right spot, with the right bullet or broadhead to achieve maximize blood loss. A quick, humane kill is the goal, and blood clotting is the enemy.

Deer are Survivors

Last fall, I shot a small-racked buck that turned out to be one of the most memorable of my hunting career. I had been hunting mornings and evenings for several days with one of my all-time favorite hunting buddies and time was running out. I had seen one good buck and several does, but so far I had been skunked.

I was in a stand I had hunted from a couple of days earlier xe2x80x94 just inside the woods and about 70 to 80 yards from the corner of a woodlot bordered by harvested cornstalks. An hour or so after daylight, a buck came down the hill into the corner of the woods. I got a good look at his rack and determined he wasnxe2x80x99t a shooter. The woods were pretty thick between my treestand and the deer, but after milling around briefly, he cut across the corner and stepped right into the open. I could hardly believe what I saw!

That buck had a softball-size hole in his side, right beneath the spine and behind the rib cage. With an obviously wounded deer, I decided I had no choice, and a .270 Win. bullet to the spine put him on the ground. A few minutes later, when I went over to the downed buck, I saw the extent of the damage caused by the earlier wound. Apparently, the day before, a spine shot went slightly too low. The deer had survived the night with that gapping wound, and when I saw him he wasnxe2x80x99t even limping or showing any signs of injury. With the extent of the wound, I could hardly believe it. Perhaps with his excellent clotting ability, he could have survived, but I felt it was my ethical duty to put him down mercifully.

In a stroke of bad luck for the first hunter, the bullet, although expanded, had failed to damage the spine. Though it took a large chuck out of the para-spinal muscles (backstraps), the wound had clotted quickly, and the deer apparently had not lost very much blood. In fact, the wound had minimal dried blood on it, and when I opened the deer there wasnxe2x80x99t much clotting from the original wound. Only the backstraps had been badly damaged, and the miracle of blood clotting kept the deer alive and moving well.

Hunt and learn. I sure learned an impressive lesson that day about the incredible blood clotting ability of deer!

xe2x80x94 Emeritus Professor at the University of Alabama, Dr. Phillip Bishop is a former NASA scientist.

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