Effect of Dietary Crude Protein Level and Supplemental Herbal Extract Blend on Selected Blood Variables in Broiler Chickens Vaccinated against Coccidiosis

SIMPLE SUMMARY: Today the poultry industry is facing mounting pressure to phase out chemoprophylaxis. One of the major threats to the poultry production is coccidiosis, a widespread parasitic disease, commonly controlled by in-feed coccidiostats. The use of immunoprophylaxis with the live anticoccidial vaccines instead of coccidiostats in broiler chickens is a promising approach; however, there is a broad reluctance to use them in intensive production due to a possible transient performance deterioration. Thus, nutritional methods such as dietary modification or herbal extracts used as complements to anticoccidial vaccination may support gaining a satisfactory performance, as well as an improved health status in broilers. ABSTRACT: Immunoprophylaxis with a live anticoccidial vaccine is regarded as the most promising alternative in place of in-feed coccidiostats in the poultry industry. An experiment, designed as a 2 × 2 × 2 factorial arrangement with 6 replicate pens per treatment and 8 male Ross 308 chicks per pen, was conducted to evaluate the effect of dietary crude protein (CP) levels (21.6% or 23.6%, during the starter phase) and a herbal extract (HE) blend dietary supplementation (Echinacea purpurea, Salvia officinalis, Thymus vulgaris, Rosmarinus officinalis, Allium sativum, Origanum vulgare; 0 or 2 g/kg of feed) on selected hematological, biochemical, redox, and immunological parameters in broilers vaccinated against coccidiosis (anticoccidial vaccine (ACV); none or 1× dose, administered at 1 d of age). The blood samples were collected at 14 d of age. Anticoccidial vaccination (p < 0.05) had a negative effect on immune responses, as shown by a reduced total white blood cells (WBC) count, a reduced lymphocytes count (L), a higher proportion of heterophils (H) in leukogram assessments, as well as H/L-ratio increase. ACV resulted in a decrease in phagocytic activity assessed as decreased percentage of phagocytic cells, phagocytic index and NBT test, as well as in reductions in plasma glucose and LDL-cholesterol concentrations, and increases in HDL-cholesterol and aspartate aminotransferase (AST) activity. In terms of redox status, ACV significantly increased the catalase (CAT) activity and ferric reducing ability of plasma (FRAP), and decreased malondialdehyde concentrations. An increase in dietary CP in vaccinated chickens resulted in higher relative L and lower relative H counts, a lower H/L ratio, a decrease in AST and an increase in CAT activities, but also a decrease in FRAP and concentrations of lipid peroxides. Vaccinated chickens fed a diet supplemented with HE were characterized by higher relative L and lower relative H counts, a lower H/L ratio, and a decrease in AST activity. A change of diet composition, such as an increase in CP content and dietary HE supplementation, can be recommended in broilers vaccinated against coccidiosis, mainly due to its positive effect in alleviating stress levels. However, the simultaneous increase of CP and HE dietary supplementation offered no additional relevant benefits in most of the blood indices of vaccinated chickens.