Use of NEFA as a Tool to Monitor Energy Balance in Transition Dairy Cows
by James K. Drackley
TAKE HOME MESSAGES
- 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
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.
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.
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.
Example of changes in NEFA of cows before and after calving (Douglas
et al., 1998).