Three studies were designed to evaluate the promoting effect of cyclopropenoid fatty acids (CPFA) on avian myeloblastosis virus (AMV) infection in White Leghorn chickens. In the first study effects on growth parameters, blood serum and erythrocyte lipid composition of White Leghorn chickens were investigated at 100 ppm and 300 ppm dietary CPFA. In comparison to controls, chicks fed dietary CPFA had reduced body weights and food intake. At both levels, CPFA increased the saturated fatty acids and decreased monoenes in blood serum and erythrocyte triacylglycerols and phospholipids. In a second study, the effects of high dietary (300 ppm) CPFA on AMV infectivity were investigated. Chicks were inoculated with 0.1 ml AMV at 7 days of age. A diet containing CPFA was fed before and after inoculation. CPFA/AMV treated chicks showed a marked reduction in body weight gain and food consumption in comparison to controls. CPFA appeared to promote AMV infection along with unexpected violent hemorrhagic manifestations. These hemorrhagic manifestations appeared to cause death before AMV induced myeloblast proliferation in the circulating blood. In comparison to controls, CPFA altered the phospholipid composition of isolated myeloblasts and the cholesterol/phospholipid ratio of isolated myelobasts, myeloblast plasma membrane, and virus particles. Analysis of the acyl group composition of choline and ethanolamine phospholipids from CPFA treated myeloblasts and myeloblast plasma membrane revealed an increase in saturated fatty acid and a decrease in monoenes. In both, CPFA appeared to affect ethanolamine more than choline phospholipids. In contrast, the alterations observed in CPFA treated virus particle choline and ethanolamine fatty acyl chains were reversed from those found in the myeloblast and myeloblast plasma membrane. In addition, ATPase specific activity was altered in relation to the CPFA induced lipid changes in the myeloblast plasma membrane and virus particle. It was shown that as saturation increased enzyme activity increased. As a third investigation, the effects of low dietary (75 ppm and 150 ppm) CPFA on AMV infection was conducted in an attempt to eliminate the hemorrhagic manifestations. A difference that was observed between this investigation and the 300 ppm CPFA/AMV study was less severe hemorrhagic responses. Histological examination of CPFA treated liver and spleen by light microscopy revealed heavy infiltration of mitotic myeloblasts into each tissue. Analysis of the number of virus particle/ml by reverse transcriptase revealed 300 ppm dietary CPFA stimulated the synthesis and release of virus particles. This was in contrast with 150 ppm dietary CPFA which retarded the synthesis and release of virus particles. / Graduation date: 1982