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Use of NEFA as a Tool to Monitor Energy Balance in Transition Dairy Cows
by James K. Drackley


  • Plasma nonesterified fatty acids (NEFA) reflect body fat mobilization in response to negative energy balance or stress conditions.
  • Measuring NEFA concentrations can be used as a tool with other factors to help diagnose problems during the transition period.

During times of energy deficit, animals break down triglycerides (fat) stored in adipose tissue. The resultant nonesterified fatty acids (NEFA) enter the blood stream to be transported to organs and tissues throughout the body. The concentration of NEFA measured in blood has been shown to reflect fat mobilized from body fat reserves. Elevated NEFA levels indicate that dietary energy intake is insufficient for the cows needs for milk production or fetal growth and that body fat is being broken down to supply the energy deficit. Researchers at Michigan State University found that increased NEFA during the late closeup period were associated with greater incidences of ketosis, displaced abomasum, and retained fetal membranes, but not milk fever, around calving. Extensive and prolonged mobilization of body fat as reflected by increased NEFA concentrations and loss of body condition generally leads to fat accumulation in the liver (hepatic lipidosis or fatty liver).

Plasma NEFA are measured by an enzymatic assay procedure. Typical changes in NEFA during the transition period are shown in Figure 1. Normal values for cows in positive energy balance are less than 200 micromolar (µM). During the close-up period, values increase slowly as the cow approaches calving, and usually range from 200 to 300 µM (0.2 to 0.3 mM) during the last week before calving. Values increase sharply from 2 to 3 days before calving and generally peak at 800 to 1200 µM on the day of calving due to hormonal changes and the stress of calving. After calving, NEFA should rapidly decrease. Values greater than about 700 µM beyond 7 days after calving indicate severe negative energy balance or health problems and suggest that transition and fresh cow management should be examined. By 3 weeks after calving, values should again be below 300 µM.

Measurements of NEFA are most useful during the closeup period and in fresh cows. Some precautions must be observed and the limitations of the test need to be understood. At least 7 cows per group (closeup and fresh) should be tested, because individual variation is large. The test assay has a coefficient of variation of about 10%, so that a value given as 500 µM actually could lie between 450 and 550 µM. Concentrations of NEFA are highest in the early morning and lowest in the late afternoon. Feeding markedly lowers NEFA. For example, University of Wisconsin researchers restricted feed offered to dry cows and heifers to simulate the feed intake depression and negative energy balance that often occurs immediately before calving. Plasma NEFA decreased sharply from about 500 µM before feeding to about 230 µM by 3 hours after feeding. Consequently, blood samples should be taken in the morning before the first feeding of the day.

Do not test cows within 3 days after calving, and closeup cows that calve within 3 days after the blood is drawn should not be included in the group average. No sick cows should be sampled because any illness or disorder increases NEFA concentrations. Excitement increases NEFA, although normal handling procedures generally do not greatly affect the measurement. Cows fed a ration containing 1 to 1.5 pounds of supplemental fat would have NEFA values about 50 µM higher than cows fed no supplemental fat. In research at the University of Illinois, we compared NEFA concentrations between first-calf heifers and older cows, both during midlactation, fed the same diets and housed in the same barn under the same management. Concentrations were 185 µM in heifers and 150 µM in cows. The higher NEFA in heifers may be associated with their greater nutrient demands for growth.

Interpretation of NEFA test results should be made carefully and always in conjunction with other information such as feed intakes, body condition, and observations of cow comfort. Elevated values in cows that appear to be comfortable and otherwise well-managed may suggest a nutritional or feeding management problem. On the other hand, values could be elevated in the presence of an apparently excellent nutritional program if cows are uncomfortable or environmentally stressed. Data to demonstrate the magnitude of NEFA increases to be expected from stress conditions during the transition are not available.

At this time, few laboratories perform NEFA analysis on a commercial basis. The Animal Health Diagnostic Laboratory at Michigan State University (phone 517-353-9312) provides good service and reliable results. They will provide sampling and shipping instructions by mail or fax on request. Blood samples should be drawn into EDTA tubes and placed on ice immediately. Cost is $5 per sample as long as at least 7 samples are sent.

Figure 1. Example of changes in NEFA of cows before and after calving (Douglas et al., 1998).

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