Effects of a soluble essential oil additive on inflammatory response, epithelial integrity, and performance of broilers subjected to an experimental infectious bronchitis virus challenge.

Infectious bronchitis virus (IBV) remains one of the major respiratory pathogens affecting broiler production, compromising performance, respiratory integrity, and immune function. This study evaluated the effects of a water-soluble additive containing eucalyptus, camphor, mint, and copaiba essential oils administered either by environmental spraying or through the drinking water to broilers subjected to an experimental IBV challenge. A total of 280 one-day-old Cobb 500 male broilers were allocated to four treatments: nonchallenged control, IBV challenge (challenged untreated group), IBV challenge plus soluble additive by spraying, and IBV challenge plus soluble additive via drinking water. Birds were challenged at 8 d of age using a 10-fold dose of the attenuated Massachusetts H120 vaccine strain, whereas the essential oil additive was administered from 9 to 13 d of age. Growth performance, antibody titers, carcass yield, relative organ weights, tracheal and spleen histology, tracheal antioxidant metabolism, and expression of genes related to immunity, oxidative stress, and epithelial barrier integrity were evaluated until 35 d of age. The experimental challenge affected productive performance, including final body weight (P = 0.0369) and feed conversion ratio (P = 0.0441), and reduced breast yield, with the control group showing a higher breast yield (27.46 %) than the challenged untreated group (24.98 %). Antibody titers differed among treatments at 16 and 35 d (P < 0.0001), with higher titers observed in challenged birds receiving the soluble additive; however, these differences indicate an altered serological response rather than evidence of enhanced protection. Qualitative histological evaluation revealed alterations in tracheal and splenic tissues following the experimental challenge, whereas additive-treated birds showed less pronounced tissue alterations. The additive was also associated with changes in oxidative status, including lower lipid peroxidation and differences in total superoxide dismutase activity, as well as modulation of genes involved in innate immune signaling and epithelial barrier function. Overall, the soluble essential oil additive modulated selected physiological, serological, oxidative, and molecular responses in broilers subjected to an experimental challenge with the attenuated H120 strain. However, the absence of a nonchallenged group receiving the additive limits the ability to distinguish challenge-dependent responses from the independent effects of the additive.