Characterization of the liver proteome in dairy cows experiencing negative energy balance at early lactation.

Negative energy balance (NEB) is associated with metabolic disorders in early lactation dairy cows. Therefore, our objective was to characterize the liver proteome in cows experiencing either NEB or positive energy balance (PEB). Forty-two multiparous Holstein dairy cows were milked either 2 or 3 times daily for the first 30 days in milk (DIM) to alter EB, and were classified retrospectively as NEB (n = 18) or PEB (n = 22). Liver biopsies were collected from 10 cows (n = 5 from each milking frequency) at 17 ± 3 DIM (NEB, n = 6; PEB, n = 4). The liver proteome was characterized using label-free quantitative shotgun proteomics and Ingenuity Pathway Analysis used to identify key affected canonical pathways. Overall, 2741 proteins were identified, and 68 of those were differentially abundant (P ≤ 0.05 and FC ± 1.5). ENO3 (FC = 10.3, P < 0.01) and FABP5 (FC = -12.5, P = 0.045) were the most dramatically upregulated and downregulated proteins, respectively, in NEB cows. Numerous mitochondrial proteins (NDUFA5, NDUFS3, NDUFA6, COX7A2L, COX6C, and COA5) were differentially abundant. Canonical pathways associated with NEB were LPS/IL-1 mediated inhibition of RXR function, oxidative phosphorylation, and mitochondrial dysfunction. Additionally, cows experiencing NEB had less hepatic IL10 transcript abundance than PEB. Together, NEB was associated with altered hepatic inflammatory status, likely due to oxidative stress from mitochondrial dysfunction. SIGNIFICANCE: Our manuscript describes the associations of negative energy balance with the liver proteome in early lactation dairy cows, when metabolic stress and the incidence of diseases is increased. Specifically, we found associations of negative energy balance with shifts in hepatic protein abundance involved in fatty acid uptake, impaired anti-inflammatory responses, and mitochondrial dysfunction. Moving forward, differentially abundant proteins found in this study may be useful as either biological markers for disease or therapeutic targets to improve metabolic adaptations to lactation in postpartum dairy cattle.