PS9-7. Proteomic Analysis Reveals Change in the Lipid Metabolism of Muscle in Beef Cattle Submitted to Early Weaning and Pasture Finished.

Abstract Early weaning and postnatal nutritional management are crucial strategies in livestock production systems and can affect long-term growth in beef cattle. This study aimed to evaluate the effect of early weaning associated with post-weaning supplementation on the muscle proteome of pasture-finished cattle. Forty male calves were assigned to early weaning (EW; 120 days, n = 20) or conventional weaning (CW; 205 days, n = 20). The EW group received protein–energy supplementation (20% CP; 78% TDN) at 10 g/kg BW/day until 205 days of age. After 205 days, all animals were raised together on pasture with protein–energy supplementation until slaughter (915 days). Longissimus thoracis muscle biopsies were collected at 205 and 915 days (pre-slaughter) and analyzed by nanoLC-MS/MS. The comparisons were as follows: (1) EW vs. CW at 205 days; (2) EW vs. CW at slaughter; (3) slaughter vs. 205 days in the EW group; and (4) slaughter vs. 205 days in the CW group. At 205 days, EW calves showed lower abundances of proteins related to lipid metabolism (CPT1B, SCP2, FABP3) and cellular stress (HSPB7), and higher abundances of proteins associated with muscle development (CSRP3, MYOZ2), compared to CW calves. At slaughter, fewer differences were observed between treatments, and the enriched pathways were primarily associated with oxidative phosphorylation; specifically, an upregulation of ATP5PF and a downregulation of NDUFB6 were observed in the EW group. Longitudinal analyses (205 days vs. slaughter) revealed distinct temporal trajectories in metabolic regulation between EW and CW groups. The transition to slaughter in both groups was characterized by the downregulation of proteins involved in mitochondrial lipid synthesis (HSD17B8) and β-oxidation (ACAA2, HADHA, HADHB, ACADS, ACADM, ACADVL, and ECI2). However, this decline was more pronounced in the CW group, which also showed a reduction in MDH2 and SDHB. Collectively, these findings suggest that the downregulation of mitochondrial oxidative metabolism at slaughter compared with 205 days was more pronounced in the CW group. An increased abundance of proteins related to lipid transport (APOD) and oxidative stress response (CFH, C3, C6, C7, and C9) was observed, along with elevated levels of complement system components. The EW group exhibited more balanced regulation, indicating improved energy efficiency and reduced inflammation throughout growth. Overall, early weaning with supplementation altered proteins related to lipid metabolism at 205 days, however, these differences were not maintained until slaughter. Funding from the São Paulo Research Foundation (FAPESP): 2022/10240-8, 2023/16301-1, and 2023/16127-1.