Longitudinal profiling of acute phase and cytokine responses in sheep supplemented with lemon essential oil during summer season.

Heat stress (HS) represents a significant environmental stressor for small ruminant production occurring during summer season, which affects feed intake, physiological homeostasis, immune function, and overall performance. Nutritional strategies based on functional feed additives, including essential oils (EO), have been proposed to enhance thermotolerance and mitigate the negative effects of HS. This study investigated whether dietary integration of lemon EO, supplied either as free oil or in microencapsulated form at two dosages, can modulate the acute phase response in sheep exposed to HS during summer season. Acute phase proteins (C-reactive protein, haptoglobin, ceruloplasmin, and albumin) and pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) was monitored for 42 days to characterize temporal dynamics of systemic inflammatory and stress responses connected with physiological responses during HS. Forty balanced dairy sheep were allocated to five dietary treatments: a control diet (CON), high-dose lemon EO (HEO, 800 mg/day), low-dose lemon EO (LEO, 400 mg/day), high-dose microencapsulated lemon EO (HEOM, 800 mg/day), and low-dose microencapsulated lemon EO (LEOM, 400 mg/day) and individually fed with a concentrate diet based on corn (50%), soybean meal (20%), barley (15%), beet pulp (12.5%), and a fat supplement (2.5 %). Blood samples were collected on days 0, 14, 28, and 42, and on plasma the concentrations of acute phase proteins (C-reactive protein-Crp, Haptoglobin-Hp, Ceruloplasmin-Cp, and Albumin-Alb) and cytokines (TNF-α, Il-6, and IL-1β) were determined by ELISA. Results showed that LEO and HEOM groups showed higher Hp concentrations than the CON group after 28 days of supplementation. Moreover, the LEOM group exhibited higher Cp levels than the HEOM group after 14 days. Albumin concentration was the highest in the CON group at day 14, whereas at day 28 it exhibited the opposite trend. Cytokine profile displayed a reduced level of TNF-α in lemon EO supplemented experimental groups, while the IL-1β level increased overall from the beginning to the end of the experiment with lower level registered in HEOM group than the CON and LEOM groups. Present data demonstrated that lemon EO influenced the acute phase protein and cytokine responses, indicating a modulatory effect on systemic adaptation to prolonged heat load during summer season.