Ketone bodies

Ketone bodies, in the strict sense, are acetoacetate and acetone resulting from spontaneous decarboxylation. These are particularly harmful due to their high oxidative potential and associated induction of oxidative damage ¹². They are not measured in the blood diagnostically, however, due to extensive efforts with regards to sample storage and analysis.

β-hydroxybutyrate (BHBA) arises from acetoacetate when there is sufficient availability of NADH + H+ and is more biocompatible. Because of its storage stability, it is more convenient for the diagnosis of (sub) clinical ketosis compared to acetoacetate and acetone ¹⁵.

However, BHBA is also formed in the rumen epithelium from butyrate if there is an adequate energy supply. Measurement of BHBA also includes decreased hepatic extraction of BHBA formed in the rumen in addition to the formation of ketone bodies in the liver. Thus, BHBA is strictly speaking an "indirect" ketosis marker.

Therefore, it is difficult to set well-founded limits for the diagnosis of ketosis.

Low limits (< 0.9 mmol/l) have good sensitivity but poor specificity and are therefore only suitable as a herd standard to derive possible health impairments.
Higher limits (1.2 – 1.4 mmol/l) feature increased specificity for the individual animal with decreasing sensitivity ¹⁸.

Cases of clinical ketosis are frequently associated with BHBA concentrations of > 3 mmol/l. In spite of this, in individual cases, cows may have serum BHBA concentrations of > 3 mmol/l without showing any clinical symptoms (own unpublished data).

Ketone bodies can also non-invasively be determined in urine and milk – but with lower precision.