Restricted ovulator hens as a novel experimental model of fatty liver disease

Fatty liver disease (FLD) is a common metabolic disorder in laying hens, characterized by excessive hepatic lipid accumulation and reduced egg production. The development of reliable experimental models is essential for improving the understanding of FLD pathogenesis and for evaluating preventive and therapeutic strategies. This study aimed to determine whether restricted ovulator (RO) hens represent an effective experimental model for FLD based on hepatic lipid accumulation and the severity of the phenotype under dietary challenge, in comparison with wild-type (WT) hens. A total of 72 Hy-Line laying hens, including 36 WT hens and 36 RO hens, were fed a normal (N), low-choline (L), or low-choline and high-cholesterol (LH) diet for 4 weeks in a 2 × 3 factorial design. All data were analyzed using two-way ANOVA, and Student's t-test or Tukey's honestly significant difference test was applied when P < 0.05. Hepatic total lipid content (% of dry and wet liver weight) was significantly higher in RO hens than in WT hens (P < 0.0001) and was further increased by the LH diet compared with the N or L diets (P < 0.0001). Hepatic triglyceride levels exhibited a significant genotype × diet interaction, with the highest levels observed in RO hens fed the LH diet (P = 0.02). The expression of genes involved in de novo lipogenesis (ACLY, ACACA, FASN, and SCD) was significantly increased by the LH diet compared with the N or L diet. In contrast, the expression of genes involved in triglyceride synthesis (GPAM and DGAT2) was significantly elevated in RO hens compared with WT hens. In conclusion, hepatic lipid accumulation was associated with diet-induced upregulation of de novo lipogenesis-related genes and genotype-associated increases in the expression of triglyceride synthesis-related genes in RO hens. Collectively, these findings support the use of RO hens as a suitable experimental model for FLD and indicate that feeding an LH diet to RO hens represents an effective approach for inducing a more pronounced FLD phenotype in laying hens.