Not if they are going to process within a couple weeks. Won't even know they are preg. How old are these heifers? I would worry more about the age than the 60 day preg for tenderness and all. If over 30 months they have to remove the spinal cord and backbone. Other than that should be fine
No issues at all. In fact I have read that being bred will increase tenderness. Back when I was raising locker beef I would turn a bull in 60-90 days before butcher. That way the heifers would not be cycling causing steers to ride them, calm them down, everyone was interested in eating, and not cycling on the date of butcher. Worked for me.