Introduction

Egg drop may be defined as a sudden drop in egg production or a failure to achieve a normal peak in production. In the autumn of 1976 a distinct egg drop syndrome was first identified in Northern Ireland. Apparently a similar disease had been seen over a 4-year period in broiler parents in Holland. The cause has been identified as Adenovirus BC14, 127, first isolated in Northern Ireland in 1976.

It affects chickens and has occurred in Ireland, Holland, France, England, Germany, Spain, Peru, Brazil, Uruguay, Argentina. Mortality is usually negligible. Circumstantial evidence suggests that the main route of transmission is through the eggs (vertical transmission) followed by latent infection during rear with viral excretion starting shortly before sexual maturity. Lateral transmission from bird to bird is slow and may be prevented or slowed for weeks by netting divisions.

Contamination of egg trays at packing stations may play a part in transmission, as may wildfowl and biting insects. Clinical disease occurs during sexual maturity. Spread from house to house may take 5-10 weeks. Unvaccinated flocks with antibodies before lay do not peak normally. The infection is commonly present in ducks and geese but does not cause disease.

Signs

• Egg drop at peak or failure to peak. Drops may be of 5 to 50% and last for 3-4 weeks.
• Rough, thin or soft-shelled eggs and shell-less eggs.
• Loss of shell pigment.
• Poor internal quality.
• Lack of signs in the birds themselves.

Post-mortem lesions

• No specific lesion - only a slight atrophy of ovary and oviduct.
• Histopathology - it may be possible to demonstrate degenerative changes in the epithelial cells of the magnum of the oviduct.

Diagnosis

History, signs/lesions (mainly lack of). Isolation of haemagglutinatin agent in duck eggs or cell culture, group antigen distinct from classical adenoviruses (white cells, throat swabs, oviduct).

Serology: HI, SN, DID, Elisa. It is important to rule out other possible reasons for egg drop, which can be caused by a large number of factors acting individually or in combination.

Management problems may be involved: inadequate water supply; extremes of temperature; inadequate lighting programme; sudden changes of feed.

Nutritional deficiency should be considered, specifically vitamins E, B₁₂, and D as well as calcium, phosporus, selenium. Diseases in which egg drop occurs, may be infectious or metabolic.

Infectious diseases include Infectious Bronchitis, Infectious Laryngotracheitis, Avian Encephalomyelitis, Newcastle disease, Marek's disease/Leukosis or any infectious disease causing a significant systemic disturbance (CRD, Coryza, Cholera, Parasites, Diphtheritic Fowl Pox).

Metabolic diseases include Fatty Liver Syndrome, intoxication by sulphonamides, insecticides or nicarbazin.

Treatment

None. Soluble multivitamins may be recommended as a non­specific measure.

Prevention

Vaccination with inactivated vaccine prior to lay.