Observations on the collection and handling of blood samples for N.E.F.A. estimation

Studies of the blood lipid pattern in healthy dairy cows

The object was to add to the knowledge of certain blood parameters of significance for charting the lipid metabolism in dairy cows. The result may be summarized as follows: Determination of the serum content of NEF A and free glycerol could be done on blood samples drawn in non-refrigerated tubes and centrifuged at room temperature within 45 min. Deep-freezing of serum did not affect the results of the analysis for these parameters. A significant diurnal variation occurred for NEFA and free glycerol. The highest values were measured in the morning, when the cows had been without feed for about 12 hrs. For glycerol (but not for NEFA) the values in the afternoon, when the cows had been without feed for 3–4 hrs., were significantly higher than those taken 2 hrs. after the morning feed. NEFA and free glycerol varied significantly with the daily yield. The NEFA content was highest at the highest level of yield, while the glycerol values were highest during the dry-period. The investigations reported under point 3, however, included no production figures during the period 21 days before to 30 days after calving. During the first month of lactation the NEFA and glycerol values showed a great mutual parallelism. The values during the first weeks of lactation were considerably higher than during the remaining lactation periods, which in all probability is a result of inevitable underfeeding of cows with good milking predisposition. During the first two days after calving there were very great variations in NEFA and free glycerol. If sampling had been consistently done during the first hrs. after calving, the values would probably have been higher throughout owing to the sympathicotonia which occurs at that time. In general, blood glucose varied less than NEFA and free glycerol with the level of yield. Thus, it seems as if blood glucose is a less sensitive measure of the energy balance. Deep-freezing of serum did not affect the values of triglycerides. No significant diurnal variation occurred for this parameter. The triglyceride values were distinctly higher during the dry-period than during lactation. No significant differences existed, however, between different production levels or during different stages of the dry-period.