Comparative liver proteome analysis of feedlot steer calves reveals growth trait-specific pathways influenced by calving season

BACKGROUND: The bovine liver is a key organ governing nutrient metabolism, immune regulation, and growth. However, the effects of birth season and growth potential on hepatic protein expression remain poorly understood. RESULTS: This study investigated the liver proteome of steer calves born during the spring and fall 2023 calving seasons (n = 5-6 steer/growth trait/season). Using a comparative label-free quantitative proteomics approach, 2,133 proteins were identified and quantified following feedlot entry. Principal component and hierarchical clustering analyses revealed distinct segregation of protein expression profiles according to both birth season (spring vs. fall) and growth trait (high vs. moderate), with calving season exerting the stronger overall influence. Bioinformatic and pathway enrichment analyses identified significant growth- and season-independent proteins. Growth-associated proteins were primarily involved in immune signaling, including antigen processing and presentation, as well as glutathione-CYP detoxification pathways. In contrast, season-independent proteins were enriched in pathways related to circadian rhythm, hormonal regulation, and muscle contraction. CONCLUSION: These results demonstrate that both growth trajectory and season of birth independently modulate the bovine liver proteome, with stronger seasonal effects, providing novel insight into the metabolic and immune mechanisms underlying variation in calf growth performance.