The trial of said action may be adjourned for not to exceed 10 days. The jury shall specify in their verdict, if they find the defendant guilty of causing or maintaining the encroachment as charged, and the extent thereof, and if the existence of the highway has been denied, they shall also specify, if they find a highway to exist, whether it be such by public use or by having been regularly laid out and established as a public highway. In the trial of any cause involving the existence of any highway, the burden of proof shall be upon the contestants to show that the same has not been regularly laid out and established as a public highway, or has not become such by public use.