By Naveen Thukral and Gavin Maguire YONG PENG, Malaysia (Reuters) – In barns filled with classical music and lighting that changes to match the hues outside, rows of chickens are fed a diet rich in probiotics, a regimen designed to remove the need for the drugs and chemicals that have tainted the global food chain. As food giants face growing pressure to offer healthier produce, Southeast Asian poultry firm Kee Song Group says its use of “good” bacteria in feed and water means it can meet one the industry’s biggest challenges: how to mass produce drug and hormone-free poultry at a reasonable price. A series of scandals in the last few years from melamine-tainted milk powder in China, horse meat supplied as beef in Europe and growth drugs causing lameness in U.S. cattle has triggered a consumer backlash over food standards and safety. Recently, Tyson Foods Inc pledged to eliminate the use of human antibiotics in chicken by 2017, one of the most aggressive timetables yet by a U.S. poultry firm.