Animals : an Open Access Journal from MDPI · 9 authors, 4 centres
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Green liver discoloration in organically reared Bronze turkey hens is a multifactorial disease linked to immune system dysfunction. Blood analyses revealed a subacute inflammatory process in early fattening (70–75 days) and acute inflammation in late fattening (120–127 days), suggesting different etiologies at each stage. Inadequate nutrient supply, particularly amino acid deficiencies, may contribute to disease development, though experimental confirmation is needed.
**Background:** Green liver discoloration (GL) in fattening turkeys has been observed for decades, often associated with Turkey Osteomyelitis Complex (TOC). In organically reared turkeys in Germany (2007–2017), GL prevalence was 27.7% in hens and 34.8% in toms, compared to 4.4% and 3.8% in conventionally reared birds. The condition is suspected to be multifactorial, with a compromised immune system as a key factor. Previous research identified correlations with immunosuppressive hemorrhagic enteritis virus in early fattening and joint/bone lesions in late fattening. Nutritional influences, beyond vitamin D₃ supplementation and feed withdrawal, had not been systematically investigated.
**Methods:** Five organic Bronze turkey farms were selected based on high GL prevalence in a predecessor study. Two consecutive trials were conducted (September 2020–March 2021 and February 2021–August 2021). From each of 10 flock samples, 20 randomly selected turkey hens were necropsied at two examination dates: early fattening (70th–75th day) and late fattening (120th–127th day). Six hens with GL and six without were selected per flock for detailed analysis (total n=130). Hematological analyses included packed cell volume (PCV), hemoglobin (Hb), total white blood cell (WBC) count, and differential counts. Clinical chemistry analyses measured albumin (ALB), alkaline phosphatase (AP), aspartate aminotransferase (AST), bilirubin (BIL), calcium (Ca), cholesterol (CHOL), creatine kinase (CK), gamma-glutamyl transferase (GGT), glutamate dehydrogenase (GLDH), urea, lactate dehydrogenase (LDH), low-density lipoprotein (LDL), magnesium (Mg), inorganic phosphate (Pi), triglycerides (TG), total protein (TP), uric acid (UA), bile acids (BA), and glutathione peroxidase (GPX). Hepatic vitamin E and selenium concentrations were determined. Feed samples (n=59) were analyzed for dry matter, crude ash, crude protein, crude fat, crude fiber, starch, sugar, apparent metabolizable energy (AMEn), amino acids, bulk and trace elements, and vitamins D₃ and E.
**Key Results:** GL prevalence was 8.7% in early fattening (range 0.0%–68.4% across flocks) and 9.4% in late fattening (range 0.0%–26.3%). At early fattening, turkeys with GL had higher WBC counts (p=0.011), higher lymphocyte counts (p=0.048), lower ALB (p=0.008), lower A:G ratio (p=0.003), lower AP (p=0.022), lower CHOL (p=0.033), higher GLDH (p=0.026), and higher GPX relative to PCV (p=0.004). At late fattening, turkeys with GL had higher WBC (p=0.007), higher heterophil counts (p=0.025), higher H:L ratio (p=0.030), lower PCV (p<0.001), lower Hb (p=0.033), lower A:G ratio (p<0.001), higher globulin (p<0.001), higher TP (p<0.001), higher Ca (p=0.002), higher Ca:Pi ratio (p<0.001), and lower CK (p=0.008). Hepatic vitamin E concentration was lower in flocks with GL at late fattening (p=0.049). Hepatic selenium (fresh matter) was lower in individuals with GL at late fattening (p=0.017). Feed analyses showed energy levels dropping below recommendations from phase 2 onward, and amino acid concentrations (particularly methionine and lysine) were generally below recommendations. Negative correlations were found between GL prevalence and supply of several amino acids (arginine, alanine, glutamic acid, glycine, phenylalanine, proline) in early fattening, and with arginine, aspartic acid, glutamic acid, proline, serine, and threonine in late fattening (all p≤0.05). Trace element concentrations exceeded legal limits in most samples (Zn: 86.54%, Se: 82.69% of samples).
**Clinical Implications:** The findings suggest two distinct pathogeneses for GL: a subacute, likely viral-associated inflammatory process in early fattening (elevated lymphocytes, low albumin) and an acute, likely bacterial-associated inflammatory process in late fattening (elevated heterophils, high globulin). The lower hepatic vitamin E in affected flocks suggests oxidative stress. While no direct causal link between specific nutrients and GL was established, the correlation between low amino acid supply and GL prevalence, combined with improved diet composition coinciding with lower GL prevalence compared to predecessor studies, suggests that optimizing nutrition—particularly amino acid and energy content—may reduce GL incidence. The study highlights challenges in formulating adequate organic turkey diets under EU regulations, including restrictions on synthetic amino acids and reliance on regional organic feed ingredients. Experimental studies are needed to confirm nutritional influences on GL pathogenesis.