This study was designed and carried out to determine the effects of dietary fat sources with various n-3: n-6 polyunsaturated fatty acid (PUFA) ratios on performance and primary antibody response in broiler chicks. Seven hundred 5-day-old male Ross broiler chicks were assigned to 35 pens (a completely random design) and fed isocaloric and isonitrogenous corn – soybean meal diets containing 0.75, 1.5, and 2.25 g/ 100 g of either fish or cottonseed oil. Diet with no supplementary oil served as control. Five to six chicks from each pen were randomly selected and either vaccinated with Newcastle disease virus (NCV) or injected (im) with 1 ml of a 5% suspension of sheep red blood cells (SRBC) on days 13 and 36, respectively. Blood samples were taken prior to immunization and every 3 to 6 days post – immunization for 3 weeks in order to collect serum and subsequent antibody (Ab) assay. Body weight (BW) and feed intake were measured on days 21, 42, and 49. There was no effect of diet on BW, gain and feed intake during periods of starter and grower, but feed consumption was more in chicks fed the diets with 2.25% of fish or cottonseed oil on finishing period (P<0.01). Chicks on the diets with the 2.25% of fish oil produced the highest anti – SRBC titers on 3, 7, 10 and 13 days after SRBC injection (P<0.05, P<0.01, P<0.05 and P<0.01, respectively). Chicks fed control or cottonseed oil (2.25%) diets produced more Ab than chicks in other groups on day 18 after vaccination (P<0.01). There was a negative correlation between BW and anti-SRBC titer on days 3 and 7 after injection (r=-0.246 and –0.383, respectively). The results showed that Ab production against SRBC in chicks fed a diet with highest ratio of n-3: n-6 PUFA was higher among the dietary groups, where moderate dietary ratio of n-3: n-6 PUFA improved Ab production against NCV.
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