This experiment evaluated the effects of an in ovo injection of conjugated linoleic acid (CLA) on immune status and blood metabolites of broiler chicks at 21 and 42 days of age. One hundred and sixty fertilized eggs were selected from a young broiler breeder flock and allocated to4 treatments with 4 replicates each. CLA was injected into the air sack of the selected eggs (150 and 300 mg, dissolved in 100 mL of commercial diluents, CLA150 and CLA300) on Day18 of incubation. Two control groups (injected with or without diluent) were also included. In ovo injection of 150 or 300 ppm CLA increased (p < 0.05) feed intake of chickens as compared to control groups up to 42 days of age. Weight gain and feed conversion ratio of chickens from CLA300, were improved (p < 0.05) as compared to chicks hatched from eggs injected diluent or control group during total period. Cutaneous basophil hypersensitivity response to injection of phytohaemagglutinin-P significantly (p < 0.05) increased in chickens from CLA300 comparing to chicks from CLA150 or control ones. In ovo injection of 300 ppm CLA, decreased blood serum cholesterol and low density lipoprotein (LDL) of chickens as compared to control chicks or those from CLA150 (p < 0.05). Central lymphoid tissues such as bursa of Fabricius and thymus relative weights were increased (p < 0.05) in chickens from CLA300 as compared to chicks injected diluent or control groups. It is concluded that feeding 300 ppm CLA through in ovo injection may be effective to subsequent growth rate, immune response and decrease blood serum cholesterol and LDL of broiler chickens during whole experimental period.

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