The objective ofthis research was to evaluate the performance, carcass yield and intestinalmorphometry of broiler chickens raised under different temperatures that receivedfeed with or without yeast extract and prebiotic in the pre-initial phase. Onethousand four hundred and forty one-day old male chicks were used, raised indifferent climate chambers. Feed with or without the addition of yeast extractand prebiotic was offered only in the pre-initial phase (1 to 7 days). Fromthe eighth day on, every chick received the same feed, readjusted accordingto usual recommendations. A randomized complete experimental design was usedin a 3 × 2 × 2 factorial arrangement, consisting of three environmentaltemperatures (hot, comfort and cold) and two levels of yeast extract (with orwithout) and prebiotic (with or without). The performance of the birds was evaluatedconsidering weight gain, feed intake, food conversion and viability at 42 daysof age. Carcass yield and intestinal morphometry were also evaluated. Environmentalheat impaired performance and carcass yield. Prebiotic inclusion in the pre-initialfeed increased weight gain and enhanced food conversion of birds raised underhot conditions. The inclusion of products in the feed of broiler chickens raisedin hot and cold environments has beneficial effects on chicken intestinal villi.
