Lactic-fermented red onion (Allium cepa L.) extract in drinking water improves feed efficiency, selectively modulates cecal microbiota, and reduces ammonia emission in heat-stressed yellow-feather chickens.

Heat stress is a major constraint to sustainable poultry production in tropical regions. This study evaluated the effects of Lactobacillus plantarum 1582-fermented red onion bulb extract (LFRO), supplied through drinking water, on growth performance, cecal microbiota, and excreta gas emissions in heat-stressed yellow-feather chickens. A total of 300 one-day-old male Rilai chicks were assigned to four treatments in a completely randomized design with five replicate pens of 15 birds each: unsupplemented control or LFRO at 25, 50, or 100 mg/L in drinking water. Birds were reared for 70 days under natural chronic tropical heat stress, with the temperature-humidity index predominantly within the severe-to-very severe range (28.9-31.1). Supplementation with 100 mg/L LFRO increased final body weight and body weight gain, reduced feed intake, and improved feed conversion ratio over the whole trial. The European Production Efficiency Index and Broiler Performance Efficiency Factor were also highest in the 100 mg/L group. Cecal 16 S rRNA sequencing showed no major changes in alpha- or beta-diversity, but several selected bacterial genera were modulated. LFRO at 50 and 100 mg/L reduced ammonia emission from excreta, whereas the other measured gases were not affected. This study shows LFRO at 100 mg/L is a natural drinking water supplement that improves feed efficiency and gut microbial balance in yellow-feathered chickens exposed to chronic tropical heat stress.