Present study was conducted to investigate the production of immune yolk against multiple avian viruses and effect of physicochemical factors on its keeping quality. It was observed that peak antibody titers in the yolk of eggs laid by the birds vaccinated against avian viruses (Newcastle disease virus-NDV, infectious bursal disease virus-IBDV, avian influenza virus-AIV-H9 and hydro pericardium syndrome virus-HPSV) were attained on 4 weeks post-boosting which were maintained over subsequent 6 weeks and started declining thereafter. The immune yolk treated with chemicals (antibiotics, sodium azide and formaldehyde) was stored at room temperature, refrigerator and freezer. Any change in physical properties (color and odor) and antibody titer of the yolk was determined at day 0, 7, 14, 22 and 30 post-storage.
Antibiotics (penicillin, streptomycin and gentamycin) in the yolk during storage at room temperature inhibited the bacterial growth but permitted fungal growth that induced physico-chemical changes such as change in color, development of bad smell and reduction in antibody titer. Antibiotics / sodium azide treatment and freezing / refrigeration for more than 30 days showed undetectable change in antibody titer of the immune yolk. However, formaldehyde
in the yolk during storage at -20°C precipitated its proteins leaving clear fluid free from the antibodies.
Effect of chemically treated stored immune yolk was investigated on the recovery of Newcastle disease virus (NDV) infected layer cockerels (35 days old). Antibiotics and sodium azide treated fresh and stored immune yolk (at 4°C for 15 days) containing 64 units of anti-ND V-haemagglutination inhibition (HI) antibodies showed 100 percent protection in the birds. The immune yolk treated with the same chemicals and stored at -20°C for 30 days also showed 100 percent protection. However, antibiotics and sodium azide treated yolk (containing same titer of the antibodies) stored at 4°C for 30 days showed 70 percent and 90 percent protection, respectively. It is inferred that sodium azide in the immune yolk during storage at 4°C or -20°C might have preserved antibodies and hence such yolk may be used for passive immunization to treat the virus infected birds.