Abstract
In this study, two experiments were performed to clarify the effect of dietary supplementation of coconut oil (CO) on the growth, immune response, hematological ,biochemical parameters and mortality of uninfected and experimentally infected rabbits with Ornithobacterium rhinotracheale (ORT) and /or mixed infection of ORT + Pasteurella multocida (P. multocida). To achieve this goal, seventy-two New Zealand White male rabbits were used in this study and divided into 3 groups of 24 rabbits each. The first experiment was represented by the first group, which explored the impact of different dietary levels of CO on normal rabbits and subdivided into four subgroups. The first subgroup fed basal diet (Control) and the second, third and fourth subgroups fed a basal diet supplemented with 1 %, 1.5%, and 2% coconut oil, respectively for 4 weeks. The second group represented the second experiment. The second group was subdivided into four subgroups and subjected to a single infection with ORT infection. The first one was kept as infected control subgroup; the second, 3rd, and 4th infected subgroups were treated with 2% coconut oil, Sulpha-trimethoprim and 2% coconut oil plus sulpha-trimethoprim respectively. The third group was similar to the second group but subjected to mixed infection with ORT+ P. multocida infection for 4 weeks. The results revealed that, the 1st experiment represented by the result of the 1st group which revealed a significant increase (P<0.05) in body weight gain (BWG), phagocytic activity (PA), phagocytic index (PI), total leukocyte counts (TLC), lymphocytes and high density lipoproteins (HDL-C), when compared with control subgroup 1.1. Also there was a significant decrease (P<0.01) in food conversion ratio (FCR), serum total cholesterol (TC), triglycerides (TG), low density lipoproteins-cholesterol (LDL-C), very low density lipoproteins-cholesterol (VLDL-C) and glucose concentrations in (CO) supplemented subgroups compared with control subgroup 1.1., with the superior effect for the highest concentration of coconut oil ( 2%). The results of the second and the third groups represented the result of the second experiment. ORT infected untreated subgroup 2.1. Moreover, the mixed infected untreated sub group 3.1. showed clinical signs and postmortem lesions of respiratory tract affections as coughing, sneezing, fever and pneumonia, increased mortality rate, significant decrease (P<0.05) in feed intake, body weight gain, phagocytic activity, phagocytic index, normocytic normochromic and macrocytic hypochromic anemia respectively, stress leukogram and a significant increase (P<0.05) in serum biochemical parameters as AST, ALT, total cholesterol (TC), triglycerides (TG), low density lipoproteins-cholesterol (LDL-C), very low density lipoproteins-cholesterol (VLDL-C) and glucose concentrations. Together with a significant (P<0.05) increase in biomarkers of renal injury; urea, creatinine and a significant (P<0.05) decrease in total proteins and albumin concentrations. Coconut supplementation (2%) played role in improving the general health condition, immune responses, the severity of adverse clinical signs, postmortem lesions, mortalities and ameliorated the deteriorating effects of ORT and/ or P. multocida infection, especially in hematology and serum biochemical parameters in all infected treated groups compared with infected untreated or infected treated groups with antibiotic only.

Key words: Coconut oil ,rabbits, growth, haematology ,biochemical,Ornithobacterium rhinotracheale , Pasteurella multocida