Determining the breed of my dog

Hello all,

I am looking for help to determine the breed of my dog. I will give you as many characteristics as I can.

His mother is a Welsh Corgi. I believe that she is a Pembroke, but I am not 100% sure if she is a pure-bred or not.

She had 4 pups.
-1 was short (natural Corgi build) with wavy hair
-1 was tall (Collie build?) with wavy hair
-1 was short with straight hair
-1 was tall (this one is mine) with straight hair

They were all born with very short tails, which tells me that the mother was at least part Pembroke. All but one were docked to be even shorter.

Traits of mine:
24 inches tall, 60 pounds. These are not exact, but pretty close. I can give exact measurements on Monday when he gets his shots.

Loves to chase things. Sheep, cattle, cats, other dogs. Does not chase balls, frisbees, sticks, etc.

VERY loyal. Always stays by my side, and will remain seated. Quick learner and very good at reading me. A loud whistle will have him sprinting to me.

Loves to explore new areas, and has an awesome nose. Loves to hunt for small critters (squirrels, gophers, rabbits). Doesn't particularly care for muskrats though.

Is very protective of himself, me, and his food. Not that picky of an eater, but won't eat certain types of treats.

I think that the father is a Border Collie, but I do not know the father. The mother was pregnant when we got her. The previous owner had passed away. The naturally short tails is what has me debating whether or not these dogs could be part Collie. Plus they aren't all that hyperactive. They get pretty excited when they see me or get to go for a ride, but are not as crazy as pure-bred Collie's that I have had in the past.

I have posted a photo of him at a year old. On the right is his sister, on the left is his mother, who has the exact build of a Corgo.