It's difficult to see but it seems to be a medium shank gag bit, possibly a Jr Cow Horse. I can't tell if the center piece of the mouth is chain or the chain I see is the curb chain. A chain as a middle piece of the mouth piece is rather mild even though it looks severe.
It's a dogbone, I rode my mare in that exact same bit and have since changed to a different version of the same bit. Be careful, the sides of the bit slide up and down ever so slightly and can pinch the sides of the mouth.
The dogbone is great for horses that are busy with their mouths, and my mare really loved the copper rollers. It's actually a fairly mild mouthpiece.