Variation in fat content between liver lobes and comparison with histopathological scores in dairy cows with fatty liver.

BACKGROUND: The assessment of a liver biopsy remains the gold standard for diagnosing and staging fatty liver in dairy cows, which is often necessary for diagnostic and research purposes. Accuracy of the diagnosis relays on the quality of the biopsy, the assumed representativeness of a small tissue sample for a disease process throughout the liver and accurate human evaluation of histologic specimens. The objective of the present study was to assess the distribution of triacylglycerol (TAG) infiltration throughout the parenchyma of livers with different degrees of fatty liver in dairy cows. In addition, histopathological scores from the corresponding specimens were compared to a quantitative measurement of TAG, as well as the agreement between two observers. METHODS: Thirty livers with different degrees of lipid infiltration were selected and 10 different locations throughout the liver were assessed. The TAG content was measured enzymatically, calculated in % or mg/g wet weight, and assigned to a scoring system. Corresponding tissue specimens were stained with hematoxylin-eosin (H&E) and Oil red O (ORO) for histopathological evaluation, using a scoring system. RESULTS: The difference in TAG content between any locations was less than 2%. Based on the scoring system the TAG concentration was even distributed in 79.3% of the livers. Based on kappa statistics the agreement between two pathologists and staining technique in scoring histological specimens was moderate to fair. CONCLUSIONS: Overall the distribution of TAG throughout the liver and the accuracy of human evaluation of liver biopsies may lead to acceptable diagnoses for clinical purposes. Within the liver lobules a common pattern of lipid distribution depending on severity could be observed. For the staging of lipid infiltration for research projects, some degree of variation needs to be considered.

Altered plasma lipidome profile of dairy cows with fatty liver disease.

Fatty liver disease is a common health problem of dairy cows occurring during the transition from pregnancy to lactation. It is a direct response to fat mobilization due to negative energy balance. Accumulation of lipids in the liver occurs if the uptake of non-esterified fatty acids by the liver exceeds the capacity of lipid oxidation or secretion by the liver. Currently, the diagnosis of fatty liver disease requires confirmation through biopsies to determine the hepatic lipid content. In view of this lack of a practical diagnostic tool, we compared the plasma lipidome of diseased dairy cows using liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. Multivariate data analysis yielded 20 m/z values that were able to distinguish between dairy cows with no hepatic lipidosis and those exhibiting different stages of the disease. Based on the chromatography retention time and m/z ratios, we identified phosphatidylcholines with reduced plasma abundances in cows with fatty liver disease. The abundances of different bile acids tended to be increased. In addition, we detected two metabolites related to inflammation, resolvin E1 and palmitoyl-ethanolamine (PEA), which need to be further investigated in cattle. These results indicate that the measurement of specific representatives of phosphatidylcholines in plasma may provide a novel diagnostic biomarker of fatty liver disease in dairy cows.

Blood plasma lipidome profile of dairy cows during the transition period.

BACKGROUND: The transition period of dairy cows, around parturition and the onset of lactation, involves endocrine and metabolic changes to compensate for an increased energy requirement aggravated by reduced feed intake. Transition cows adjust to the resulting negative energy balance with the mobilization of lipids from the adipose tissues yielding increased blood levels of non-esterified fatty acids and ketone bodies like ß-hydroxybutyrate. RESULTS: To study the biochemical adaptations underlying this physiologic adjustment and possible pathologic derangements, we analyzed the blood plasma lipidome of transition cows by ultra-pressure liquid chromatography coupled to high-resolution quadrupole time-of-flight mass spectrometry. The resulting data were processed by principal component analysis, revealing over 60 lipid masses that change in abundance over the test period ranging from two weeks before calving to four weeks postpartum. Further characterization of analytes by tandem mass spectrometry demonstrated that the concentration of triacylglycerides in plasma drops at the day of parturition whereas the plasma level of many phosphatidylcholines and two sphingomyelins increases steadily during early lactation. CONCLUSION: This newly identified shift in phospholipid composition delivers a potential biomarker to detect aberrant metabolic pathways in transition cows and also provides insights into how to prevent and treat associated disorders like fatty liver disease.