l-carnitine plays an important role in energy metabolism through supporting the transport of activated fatty acids to the subcellular site of β-oxidation. An acute phase reaction (APR) is known as an energy consuming process. Lipopolysaccharides (LPS) are often used in animal models to study intervention measures during innate immune responses such as APR. Thus, the aim of the study was to investigate the effects of dietary l-carnitine supplementation during an LPS-induced APR in mid-lactating German Holstein cows. Animals were assigned to a control (CON, n = 26) or l-carnitine group (CAR, n = 27, 25 g rumen-protected l-carnitine/cow/d) and received an intravenous injection of LPS (0.5 μg/kg body weight) at day 111 post-partum. Blood samples were collected from day 1 pre-injection until day 14 post-injection (pi). From 0.5 h pi until 72 h pi blood samplings and clinical examinations were performed in short intervals. Clinical signs of the APR were not altered in group CAR except rumen motility which increased at a lower level compared to the CON group after a period of atonia. Group CAR maintained a higher insulin level compared to group CON even up to 72 h pi which might support glucose utilization following an APR.

This study investigated the effect of body condition around calving on the hepatic mRNA expression of genes involved in fatty acid (FA) metabolism and mitochondrial protein import system of dairy cows during the transition period. Fifteen weeks before their anticipated calving date, 38 multiparous Holstein cows were selected based on their current and previous body condition scores (BCS) and allocated to either a high or a normal BCS group (19 cows each). They received different diets to reach targeted differences in BCS and backfat thickness (BFT) until dry-off. At dry-off, normal BCS (NBCS) cows had a BCS <3.5 and BFT <1.2 cm, and the high BCS (HBCS) cows had a BCS >3.75 and BFT >1.4 cm. The expression of targeted genes in the liver was assayed by reverse-transcription quantitative real-time PCR using microfluidics integrated fluidic circuit chips on a subset of 5 cows from each group. Liver biopsies were collected at d −49, +3, +21, and +84 relative to parturition. The mRNA abundance of 47 genes related to lipid metabolism including carnitine metabolism, FA uptake and transport, lipoprotein export, carnitine metabolism, mitochondrial and proximal FA oxidation, ketogenesis, AMP-activated protein kinase/mammalian target of rapamycin pathway, and mitochondrial protein import system was assessed in liver tissue. The mRNA abundances of FA binding protein (FABP)6 (in both groups), and FABP1 and solute carrier family 22 member 5 (SLC22A5) in HBCS were upregulated (>1.5-fold change, FC) in early lactation (at d +3 and +21 postpartum) compared with antepartum (d −49), indicating promoted FA uptake and intracellular transport in the liver due to the metabolic adaptations of elevated lipo-mobilization after parturition. The upregulation of SLC22A5 and SLC25A20 after parturition was more pronounced in HBCS than in NBCS cows, suggesting a need for increasing the capacity of FA uptake, and FA transport into the hepatocyte. The increased mRNA abundance of carnitine palmitoyltransferase 1A, after parturition and to a greater extent in HBCS (FC = 4.1) versus NBCS (FC = 2.1) indicates a physiological increase in the capacity of long-chain fatty acyl-CoA entry into the liver mitochondria compared with antepartum (ap; d −49 relative to calving). The greater hepatic mRNA abundance of genes encoding enzymes involved in mitochondrial FA oxidation in HBCS than in NBCS points to an increased rate of mitochondrial β-oxidation. The hepatic mRNA abundance of 3-hydroxy-3-methylglutaryl-CoA synthase 2 and 3-hydroxy-3-methylglutaryl-CoA were upregulated after parturition (d +21/d +3 pp) to a greater extent in HBCS than in NBCS cows, indicating that excess acetyl-CoA generated via β-oxidation was increasingly used for ketogenesis. We observed for the first time that the mRNA abundance of genes involved in the translocase of the inner membrane (TIM) complex (TIM22 and TIM23) in the hepatic mitochondrial protein import system were undergoing distinct changes during the transition from late pregnancy to early lactation in dairy cows. Even thoug...

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