Which of the following is true about the horse's frog?

The horse's frog is a significant part of its hoof anatomy, specifically located on the underside of the hoof. One of its primary functions is indeed to play a critical role in blood circulation. This is achieved through its unique structure: the frog is a wedge-shaped, rubbery tissue that acts as a pump. When the horse walks or moves, the frog expands and contracts, applying pressure to the digital cushion inside the hoof, which in turn facilitates blood flow back up the leg. This process is vital for maintaining healthy circulation in the lower limbs of the horse.

The other choices touch on different aspects of hoof anatomy but do not accurately represent the frog's primary functions. The frog is not the primary weight-bearing structure of the hoof; that role is predominantly served by the hoof wall and sole. While moisture regulation is an important consideration for overall hoof health, it is not primarily the frog's function. Additionally, the frog is located towards the back of the hoof rather than the front, which further highlights why the other options do not align with the frog's actual role in equine physiology.