Abstract: A pharmaceutical composition to be administered to avian species, especially poultry, either into the drinking water or into the diet or to be aerosolised over the hens, consisting of a vehicle system comprising a mono-/di-, ester-/etherglycerides conjugated with water-soluble polymer groups selected from PEG's containing 2-30 polyoxyethylene units, an antigen and optionally a bacterial toxin, preferably CTB, are useful for the production of antibodies in egg yolk. The conjugated glycerides are able to augment the production of antibodies ex-vivo in egg yolk, minimizing animal stress and invasive procedures.