|Abstract:||During the periparturient period (3 wk before calving to 3 wk after calving) dairy cows commonly experience a negative energy balance due to the increased nutrient requirements for fetal growth and milk production coupled with decreased dry matter intake (DMI). This combination can increase the risk of developing certain immunologic problems and metabolic disorders like oxidative stress, ketosis, and fatty liver. Two experiments were conducted to evaluate 1) hepatic microRNA (miRNA) involvement in periparturient Holstein dairy cows supplemented methionine and 2) how body condition score (BCS) in late pregnancy impacts hepatic biomarkers involved in energy metabolism.
Previous in silico work relevant to fatty liver disease and ketosis revealed miRNAs may play a role in variety of important biological pathways including, fatty acid metabolism (miR-186, -200b and c, -218, -369) and oxidative phosphorylation (miR-101, -142, -186, -200b, -200c, -218, and -369). The main objective of the present study was to verify the expression of these miRNA and examine the relationship they may have in cows supplemented methionine during the peripartal period. Nineteen multiparous Holstein cows were fed experimental treatments consisting of a basal control diet (CON; n = 11) and CON plus Methionine (MET; n = 8). (at a rate of 0.08% on a dry matter basis) (Smartamine M, Adisseo NA). All cows received the same far-off, close-up, and lactation diet. Liver biopsies were performed at −10, 10, and 30 d relative to calving for analysis of miR-218, miR-369 5p, miR-200b, miR-200c, miR-142 3p, miR-142 5p, miR-101, and miR-186 abundance via qPCR after normalization with 3 internal controls. Results indicated that MET cows had less expression of miRNAs that were predicted to downregulate oxidative phosphorylation and fatty acid metabolism, compared to CON. Considering that MET cows had greater overall DMI there is a possibility that they were experiencing less oxidative stress in the liver, as opposed to CON, but the relationship is still unclear. Further analysis of gene targets and protein expression relevant to miRNAs presented in this study will provide more insight into the biological importance of miRNAs.
In the second study, twenty-six multiparous Holstein cows at 4 wk were divided into 2 groups based on BCS, BCS ≥ 3.50 (n = 13; HiBCS) and BCS ≤ 3.25 (n = 13; LoBCS). In the prepartum, LoBCS cows had greater DMI compared to HiBCS cows (P = 0.06). In the postpartum, LoBCS continued to have greater DMI, but HiBCS cows averaged 5.34 kg/d greater in milk yield comparatively. Plasma sampled at d −30, −10, 7, 15, and 30, relative to calving indicated increased concentrations of biomarkers related to negative energy balance in HiBCS cows. In contrast, LoBCS had greater plasma concentrations of biomarkers that have antioxidant properties, thus suggesting a potential relationship with oxidative stress. Liver tissue harvested via biopsy at −15, 7, and 30 d relative to calving and used to evaluate protein abundance via western blotting. We were unable to detect any expression of nuclear factor erythroid 2-like 2 (NFE2L2) or p-NFE2L2 (both are involved in antioxidant signaling pathways) at any time point in liver tissue. However, LoBCS cows had increased abundance of proteins associated with glutathione metabolism, an antioxidant that is capable of preventing overloads of reactive oxygen species (ROS), compared with HiBCS. miR-369 5p, miR-186, and miR-200b, which downregulate fatty acid metabolism and oxidative phosphorylation, had decreased expression in HiBCS cows, which is contrary to the patterns of decreased oxidative stress in LoBCS cows we observed in plasma biomarkers and protein abundance. In conclusion, the differences between production data, blood biomarkers, miRNA expression, and protein abundance underscore a potentially important interaction between energy metabolism in relation to BCS during the periparturient period.