Veterinary/zoology session

Dairy animals during the last days of their pregnancy and a few weeks after the delivery phase situation of negative energy balance (NEB) due to high productivity and lack of dry matter intake. The animal in NEB tries to re-establish its energy to the normal level by releasing free fatty acids or non-esterified fatty acids (FFA or NEFA) from its own fat tissues. As a result of NEFA mobilization ketone bodies are produced which are acting as precursors of several metabolic diseases such as ketosis, fatty liver, abomasal displacement, etc. Elevated blood NEFA (> 0.4 mmol/l) in dry cows is an indicator of the animal being in the condition of NEB. Scientists and companies are working intensively for newer, better and faster methods measuring the level of NEFA in the blood even in farm condition.

In our study three methods were used and compared for measuring serum-NEFA: an enzymatic colorimetric (“gold standard”) method and a non-enzymatic, colorimetric method used in laboratory condition, and another simple colorimetric method on DVM-NEFA® device. The latter is a portable one-wavelength photometer applied as a “cow-side” test in farm conditions.

Two groups of holstein-friesian (HF) cows tested immediately after calving served as “high NEFA” animals as they were physiologically in NEB. Dry HF cows and Awassi ewes 2 months after lambing formed “low NEFA” groups as physiologically they were not in NEB. All three methods showed high NEFA in the fresh cows’ serum (n=13) as expected in the sampling that occurred in January 2008. Mean values were 0.742 ± 0.310 mmol/L, 0.315 ±0.141mmol/L, 0.309 ±0.176 mmol/L with DVM-NEFA, enzymatic, and non enzymatic methods, respectively (p<0.05). Correlation between results were strong (r2=0.813-0.924). In May 2008 fresh cows’ (n=15) NEFA results were 0.795 ±0.450, 0.452 ±0.242 and 0.309 ±0.185 mmol/L with the three methods (p<0.05) with similarly strong correlations. As for “low NEFA” groups, in dry cows (n=16) serum NEFA were 0.212 ±0.094, 0.083 ±0.062 and 0.071 ± 0.064 mmol/L, respectively (p<0.05). In ewes’ serum (n=14) NEFA results were similarly low with all three methods, but significantly different from each other (0.462 ±0.239, 0.062 ±0.044 and 0.037 ± 0.037 mmol/L, respectively; p<0.05). Both in dry cows and in sheep a strong correlation was found between NEFA results achieved by the three methods (r2=0.825-0.958).

As in all groups DVM-NEFA results were 2-5 times higher than those measured by the other two methods, this the cow-side test is not recommended for use, or the widely accepted 0.4 mmol/l NEFA as upper reference limit for healthy ruminants should be re-evaluated when using DVM-NEFA.