I have 17 heifers that are roughly 18 months old and have been with a bull for 3 months. I noticed today that some of the heifers were riding each other. I hadn't noticed this behavior for some time. Do heifers sometimes do this even if they are bred just playing around, or is it always a sign they are in heat? If it's a sign of heat, our bull must have been lying down on the job.