Can't find in written citations except that of Chavez y Gilbert, but "dogal" for a stray calf is used by Hispanic cowboys in New Mexico. Chavez y Gilbert is reporting usage. It also means a nose halter. These usages may be local; elsewhere it means a neck halter or a hangman's noose. In a common phrase, it means to be in a tight spot.
I don't know the truth of it, but I tend to stick with Chavez.

Ramon F. Adams says that there has, "in recent years, been some controversy over its origin."