Oregano extract (Origanum vulgare) in female broiler chickens of free-range strain raised in the Western Amazon

ABSTRACT This study aimed to evaluate the effect of oregano extract added to commercial diets on zootechnical performance parameters, carcass yield, immunological conditions, morphometry, and intestinal pH for free-range broiler chickens raised under sanitary challenge conditions. Three hundred chicks of the strain ‘Heavy red’ were used and distributed in a completely randomized experimental design with five treatments and six replications, totaling 30 experimental units, each consisting of 10 birds. The treatments were: T1: Basal diet without oregano extract (OE); T2: Basal diet with OE (150 mg/kg); T3: Basal diet with OE (250 mg/kg); T4: Basal diet with OE (350 mg/kg); T5: and Basal diet with OE (450 mg/kg). There was a significant effect on feed intake, weight gain, feed conversion, feed efficiency, heterophil/lymphocyte ratio (H/L), and intestinal morphometry. No significant differences were observed in viability, carcass yield, intestinal pH, lymphoid organs, gizzard, heart, and intestine. Oregano extract influenced the liver yield and abdominal fat of broilers. Overall, the inclusion of oregano extract at the level of 350 mg/kg provided better results.