Fatty liver in birds at the Zoological Society of London.

The livers of 531 captive wild birds necropsied at the Zoological Society of London were examined histologically. Marked fatty infiltration of the liver was found in 13 cases. Seven of the 13 cases were from the order Psittaciformes indicating that some species (cockatoos, parakeets and parrots) in this order may be particularly susceptible to fatty infiltration of the liver. Affected livers were commonly swollen or enlarged, pale, white or yellow in colour and soft, friable or fatty at post mortem examination. Histologically, marked fatty infiltration of the liver was characterised by the presence of intracytoplasmic fat vacuoles within hepatocytes without zonal or lobular distribution throughout the sections examined. Reticulolysis and fibrosis of the hepatic parenchyma were found in association with marked fatty liver in a proportion of cases. Macroscopic or histological evidence of hepatic haemorrhages was not found in affected birds. In psittacine birds, obesity was frequently seen at post mortem examination and it was considered that nutritional and/or metabolic factors were important causes of fatty liver in this group. Fatty liver was found in association with chronic wasting diseases caused by mycotic infection in two cases.