Simple SummaryPrevious studies indicate that green liver discoloration in fattening turkeys, which has occurred with a high prevalence in organically reared turkeys, is not caused by a certain pathogen but by a variety of factors weakening the immune system. Other than vitamin D3supplementation and feed withdrawal, the influence of the provided feed, including nutrient and energy content, has not been investigated. This study aimed to investigate the state of the immune system and liver function of affected turkey hens and to determine a possible nutritional influence on the pathogenesis. Hematological analyses, clinical chemistry analyses, and determination of vitamin E and selenium liver concentrations at 2 examination dates (70th to 75th and 120th to 127th day of fattening, respectively) as well as feed analyses throughout the whole fattening period were performed. The results indicate a subacute inflammatory process in flocks with the occurrence of green livers at the early fattening stage and acute inflammation in individuals with green livers at the late fattening stage. It is suspected that an inadequate nutrient supply contributes to the development of green liver discoloration, but further research under experimental conditions is needed.AbstractGreen liver discoloration (GL) in fattening turkeys is suspected to be a multifactorial disease complex with a compromised immune system as the key factor. This study aimed to identify the formal pathogenesis of GL and to investigate possible nutritional influences. A total of 360 Bronze turkey hens out of 10 flocks from 5 fattening farms were necropsied for detection of GL during 2 consecutive trials on 2 examination dates each (70th to 75th and 120th to 127th day of fattening, respectively). At each examination date, hematological and clinical chemistry analyses, as well as determination of vitamin E and selenium concentrations in the liver, were carried out in 6 hens with (if applicable) and 6 hens without GL, representing a total of 130 individuals. Raw nutrient, energy, amino acid, bulk and trace element, and vitamin E and D3concentrations were analyzed in feed samples for each of the five feeding phases during each trial. The results of the hematological analyses, clinical chemistry analyses, and determination of vitamin E and selenium liver concentrations were statistically evaluated between: (i) individuals with and without GL, and (ii) individuals from flocks with and without turkeys with GL. At both fattening stages, the occurrence of GL was characterized by an inflammatory reaction. A subacute inflammatory reaction was detected in the early fattening stage, indicating a viral cause of the disease. In the late fattening stage, acute inflammation indicated a bacterial cause of the disease. The results of the feed sample analyses of the different flocks were generally quite homogeneous. However, the nutrient and energy content of the feed likely contribute to GL pathogenesis.