The objective of this study was to investigate the effects of dietary oils on growth performance of broiler chicks vaccinated with La Sota vaccine against Newcastle disease. One hundred and seventy five 1-week old Ross PM3 male broiler chicks were randomly allocated to five dietary groups (n = 35 chicks/group) and fed diets supplemented with 0.5% sunflower oil (Group A), 0.5% olive oil (Group B), 0.5% beef tallow (Group C), 0.5% conjugated linoleic acid (CLA, Group D) or 0.5% hazelnut oil

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... E) for five weeks. Diets contained 230 g crude protein/kg and 12.97 MJ metabolisable energy (ME)/kg (starter diet); 220 g crude protein/kg and 12.97 MJ ME/kg (grower diet) or 200 crude protein/kg and 12.97 MJ ME/kg (finisher diet). The broiler chicks were vaccinated with La Sota Newcastle vaccine at 22 days of age. Body weights were measured weekly and carcass characteristics and some organ (liver, heart, gizzard and intestine) weights were determined after slaughter. The growth rates of broilers from the Groups A, C and E were negatively influenced by vaccination, compared to Group D, which maintained its growth rate. There was no difference in the proportions of abdominal fat (%) of the chickens among the groups. The respective relative organ weights did not differ significantly between the respective dietary treatments. This study showed that the broiler chicks fed a diet supplemented with CLA had significantly better performance and carcass weights compared to the other groups. The present study also indicated that CLA included at a level of 0.5% in the diet prevented weight loss due to vaccination. _______________________________________________________________________________________