It takes muscle to compete in the Sonoma County Fair. Prince and Sheila E., two handsome young hogs at Bivalve Dairy, are on a fitness regimen, hiking every afternoon with their owner Eva Taylor ahead of next month’s contests. Eva said the hikes build strength and stamina for the show ring. On the Point Reyes Station dairy, new calves are learning to drink milk from a bucket, and Roomba-like robots are scraping out the barns.…