This is a calf puller, also known as a calving jack or fetal extractor. It is a veterinary instrument used to assist in the delivery of a calf during a difficult birth, a condition called dystocia. 

The tool works by applying controlled, steady traction to the calf, helping to guide it out of the birth canal when the cow is unable to deliver it on its own. This particular model appears to be a ratchet-style calf puller, which uses a lever and ratchet mechanism to apply force incrementally, allowing for a more controlled pull. The A Shape brace is placed against the cow's rear, and chains or ropes are attached to the calf's legs to provide the pulling force