Cow hooves are made of a protein called keratin, which is the same protein that makes up hair, fingernails, horns, and feathers. Hooves are not one solid piece, but rather grow in layers, with dead cells making up the hard, outer shell of the hoof called the hoof wall. The hoof wall is the strongest horn and most important for bearing weight, while the sole horn is the equivalent to the footpad on a dog or cat. The junction between the wall horn and sole horn is called the white line, which is made up of weaker horn. The inner claw of a cow hoof is equivalent to the middle finger of a human hand. Hooves grow continuously, and in nature, wild animals wear down their hooves as they continuously grow. However, captive domesticated species often require specific hoof care for a healthy, functional hoof. Hooves can be trimmed with a sharp knife while the cow is restrained and positioned with ropes, or with angle grinders and some type of hoof trimming crush to make the process quicker and less physically demanding.