Ketosis occurs when energy intake is low, and fat is used as an energy source.

Mobilization of body fats converts them into non-esterified fatty acids (NEFA), leading to an increase in NEFA levels above 200 micromoles per liter.

NEFA can be utilized in three ways:

Converted into energy by liver cells (the preferred pathway).
Converted into ketone bodies by the liver (less desirable).
Stored in the liver (undesirable and can lead to fatty liver).
The liver is the primary organ for converting fat into energy (glucose). However, liver output is limited. The precursor for energy production is propionate (an intermediate compound). If this glucose precursor is not available, fats are converted into ketone bodies (acetone, acetoacetate, beta-hydroxybutyric acid). If fat intake is excessive, the liver will start producing ketones.

Type I Ketosis
Ketones are also an energy source, but they are less efficient and can cause discomfort in cows. Reduced feed intake leads to increased fat burning and higher ketone production. At this point, the cow has developed subclinical ketosis.

Type II Ketosis
This type results from the fat cow syndrome. In this case, dry matter intake decreases before calving in very obese cows. It can also occur when a cow’s access to dry matter is limited before calving, or when the population of cows is high and dry matter is not well managed. Managing Type II ketosis is very challenging, and affected cows may not respond well to treatment. Type II ketosis can also result from infectious diseases such as mastitis or metritis, or from metabolic disorders like acidosis or milk fever.

Another type of ketosis is caused by butyric acid, which occurs due to direct ketone consumption from the diet. This event leads to poor dry matter intake and energy drops similar to Type I ketosis.

Clinical Signs
In cows with ketosis, it may be possible to smell ketones (acetone) in their breath. Cows lose their appetite, and milk production decreases. Reduced dry matter intake due to ketosis and fatty liver can lead to a drop of 2 to 4 kilograms in peak milk production. We know that a decrease of one kilogram of milk production at peak lactation results in a loss of 180 to 240 kilograms of additional milk over the entire lactation period.

Fat-to-Protein Ratio
Normal: 1 to 1.5
Greater than 1.5 indicates ketosis:
Increased fat mobilization
Decreased milk protein due to lack of dietary energy
Less than 1 indicates acidosis.
Diagnosing Ketosis
The minimum sample size for herd-based tests is 12 cows. This number ensures data reliability. If 10% of cows exceed the standard level, a warning level is introduced (2 out of 12).

Herds with ketosis issues show a significant increase in displaced abomasum and culling rates within the first 60 days postpartum.

The gold standard test for subclinical ketosis is measuring beta-hydroxybutyrate (BHB), as this ketone body is more stable in the blood than acetone and acetoacetate. This test is performed on blood serum, and samples should not be collected from the mammary vein. The red line is set at 1400 micromoles per liter or 14.4 milligrams per deciliter. Cows exceeding 1400 are three times more at risk for abomasal displacement.

Some references consider the red line to be 1200 micromoles.

In clinical ketosis, this number can exceed 3000 micromoles.