Extraction, quantification and distribution of the major lipid fractions in small liver biopsies of cows in transition period

摘要

There are difficulties in understanding changes in the distribution of the major lipid fractions in the liver of dairy cows due to the need for invasive techniques for sampling and relatively large quantities of sample needed for analysis. The objective of this research was to integrate a method for extracting total lipid (TL) with the enzymatic determination of its fractions in small biopsies. Liver biopsies from 60 Holstein cows in the transition period (between day 270 of gestation and 20 postpartum) underwent TL extraction using Hexane-Isopropanol mixture. TL obtained was dissolved in hexane, several aliquots of different volumes were used for the enzymatic determination of: triglycerides (TG), phospholipids (PL), total cholesterol (TC) and free fatty acids (FFA). The amount of liver sample used was 49.6 mg ± 18.45mg (Mean ± Standar Deviation). The average was 7.20% TL. The average coefficient of variation (CV) in TL extraction was 7.62%. TL. TG, PL, TC and FFA represented 52.5%; 18.30%; 19.30% and 0.41% respectively of the TL. CV for enzimatic determinations of TG, PL, TC and FFA were: 5.2%; 9.9%; 6.1% and 4.0% respectively, indicating that this method is suitable for determination of lipid fractions in small liver samples. High correlation coefficient was observed between TL and TG (0.96); while for TL and PL was -0.42; and for TL and TC -0.62; It is indicating that the increase in hepatic lipid occurred mainly in the TG fraction and consequently showed a relative decrease in the fractions PL and TC.