In summertime, cows wait under a canopy to be milked at Mark McAfee’s farm in Fresno, California. From his Cessna 210 Centurion propeller plane, the 63-year-old can view grazing lands of the dairy company he runs that produces products such as unpasteurized milk and cheese for almost 2,000 stores. Federal regulators say it’s risky business. Samples of raw milk can contain bird flu virus and…