Humoral immune responses to vaccination against Newcastle (NDV) and infectious bursal disease (IBD) virus as well as effects of Salmonella typhimurium lipopolysaccharide (LPS) injection on liver fatty acid profile were studied in the modern 2000 and the random-bred 1957 broiler chicks maintained on ad libitum as against restricted feeding regimens. Two hundred and seventy five d-old broiler chicks of 2000 and 1957 strains were randomly divided among 64 pens, half of each strain being kept on feed-restricted diet, from d 4 receiving 76, 70, 80 and 90% of the estimated feed intake (through weeks 1 to 4), respectively (factorial 2 x 2 ). To determine antibody titers, two chicks per pen were randomly selected, vaccinated against NDV and IBD on d 21 and 35, and then bled on d 21, 35, and 42. To obtain the liver fatty acid profile,6 chicks from each strain and feeding regimen(n24) were removed from each group pens (on d 0,7,14, and 28), individually housed, and fed on their original feeding regimens. Three chicks in each group were injected with LPS on a day before each experimental period (d 6, 13, 27 and 41). All chicks were slaughtered on the days following injections, with their liver samples being dissected out. Anti-NDV titers in primary and secondary responses in 1957 strain were greater than in strain 2000 (P0.0001); but, anti-IBD titer being not affected by strain (P>0.05). Feeding regimens had indicated effect on humoral immune response (P>0.05). Liver fatty acid profile was affected by strain, feeding regimen, LPS-injection, age, as well as their interactions (P<0.05). In conclusion, the results in this study confirmed the negative effect of selection for weight gain on humoral immune response. In addiation, production of catabolic pro- inflammatory mediators from n-6 PUFA precursors was more in the 2000 strain than in 1957 strain. Since the same differences were observed between chicks under two feeding regimens it is concluded that, restriction might reduce production of inflammatory mediators with an adverse effect on growth.
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