I have a question? are deers neck bigger or smaller during the rut or only when it gets cold out? the reason why is because i seen a Nice 4x5 yesterday during the late Bow season, I couldnt taken a shot but i'm waiting for a bigger Buck any ways, this buck had a small neck, this morning i seena buck with a huge neck!! Can anyone explain whats going on?

Yeah they get thicker from fighting and rubbing there antlers against the trees.

Bingo.

itsall about and preparing for the rut

One thing to keep in mind. The only purpose of antlers is to enable a buck to fight for dominance. It serves no other purpose. Given that, the extra work a buckperforms during the rut swells the neck(fighting, sparring, rubbing trees.) I would also assume that there is some biochemical (hormones) influence going on that sends fluid to that area.

I would bet that the buck with the smaller neck was a younger buck or a really old buck, regardless of antler size. The big neck bucks get is a factor of several things and is actually a hypertrophy (increase in size)of the muscles of the neck. Just like a weight builder that lifts weights, part of the reason that bucks necks increase in size is that they "work out" preparing for the rut. Pushing against each other and pushing against trees. Hormones of course have a role too just like anabolic steroids that bad boy atheletes take cause their muscles to get bigger. Don't know all the mechanisms, but older bucks tend to have bigger necks. That said, it seems to go the other way when they get really old and don't get as big anymore.

The big neck is definately "meat" though. I can cut many more pounds of hamburger off the neck of a rutting buck than I can from a nonrutting one.

Bucks necks aren't filled with fluid. They are just get big and muscular from rubbing and fighting. With all the testosterone flowing through their veins this time of year, it's like being on steroids. A buck can make 3000+ rubs in one season. Bigger bucks will have more muscle mass to begin with meaning bigger necks when at full swell. Like the one guy said, it's all about being in better shape for fighting to win dominance for the does.

Wow, everyone gave you the right answer. Not much to add.

Except, let me clarify my statement about fluid amounting for the swelling. Yes, it is increased muscle mass, but muscle tissue is approximately 80% water. I wan't trying to say the neck swelling is due to just a fluid build up. Just thought I would clear that up.