Non-estrified fatty acid (NEFA) levels can evaluate the energy status of just-fresh cows. And, they also help predict the likelihood of metabolic disorders. But proper sampling is necessary to get accurate readings.
An article in the May edition of Journal of Dairy Science confirms the importance of taking blood samples several hours after the first feeding in the morning rather than taking samples prior to the first feeding. If you take samples before the first feeding, NEFA levels may be elevated because the cows haven't eaten for an extended period of time, points out study co-author Todd Duffield, animal scientist at the University of Guelph in Canada. In fact, the study found, if samples are taken one hour before the first feed delivery of the day, there is twice the probability of detecting animals with NEFA values greater than or equal to 0.4 millimoles per liter than if samples are taken from the same cows four to 10 hours after feeding. It is necessary to take samples at a consistent time relative to feeding to avoid confounding and misinterpretation of results, the authors said.