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Subclinical ketosis, BHB levels and B vitamins

Hélène Leclerc Published on 31 December 2012

0113ca leclerc 1The transition period is a challenging time for the dairy cow. Her metabolism needs to adapt rapidly from a non-lactating to a lactating stage, in preparation for the forthcoming calving.

In addition, the reproductive system is preparing ovulation for the next breeding period.



This sudden change increases the glucose demand from the mammary gland and the fetus, which cannot be met solely by the liver.

In order to meet this demand, muscle tissues spare glucose, while fat tissues are mobilized to produce non-esterified fatty acids (NEFA) as an additional energy source.

Fat tissue mobilization is triggered by the insulin resistance mechanism, which is more active during the prepartum period. Elevated blood NEFA will reduce dry matter intake and the responsiveness of fat tissues to insulin, leading to greater fat tissue mobilization and higher blood NEFA, creating a vicious cycle.

This adaptive metabolism becomes detrimental to the cow when the extent of fat tissue mobilization is more important than the liver’s capacity to metabolize it. The result is an incomplete oxidation of the fat, which leads to the production of BHB (beta hydroxybutyrate).

High BHB levels are an indication of subclinical ketosis, a metabolic disease occurring during the post-calving period. The incidence rate of subclinical ketosis is estimated at 43 percent but can vary from 30 to 60 percent. Estimated economic loss varies from $50 to $100 per case.


To evaluate the incidence of subclinical ketosis on farms, it is proposed to measure blood BHB levels of transition cows by using a cowside blood test with BHB strips – using a pocket-sized meter.

To identify subclinical ketosis, different BHB thresholds have been identified and vary according to the sampling time period. Research suggests a sampling period from three to 16 days in milk (DIM), with a blood threshold of 1.2 mmol per L. It appears that the highest number of positive cows occurs at five DIM.

Reduced milk production is directly linked to subclinical ketosis, hence blood BHB levels. During the first 30 DIM, each 0.1 mmol per L exceeding threshold (1.2 mmol per L) is linked to a milk production loss of 0.5 kg per day.

Moreover, cows identified with subclinical ketosis were reported to be three times more likely to be removed from the herd during the first 30 DIM. Increased risk of metritis and displaced abomasum has also been related to higher level of blood BHB.

Impaired fertility is not always directly linked to subclinical ketosis, but negative energy balance affects fertility during the pre and postpartum periods.

B vitamins for a successful transition
It is well understood that energy balance needs to be improved during the transition period. Maintaining dry matter intake (energy intake) during the week before calving is essential to reduce the extent of the negative energy balance.


The energy and protein density of the transition ration, as well as feeding management, are important factors in the equation of a successful transition period, but some essential micronutrients are often disregarded.

B vitamins have been identified as being critical during the transition period due to their direct and indirect roles for immune function, liver health, energy metabolism and reproduction.

Folic acid and vitamin B12 improve energy balance by reducing fat tissue mobilization. Methyl donors, like choline and folic acid, reduce fatty liver by increasing the production of fat transport proteins (VLDL).

During the transition period, choline use is prioritized toward milk production at the expense of liver function. Folic acid’s role becomes more important to improve liver health. Increasing the exportation of fat from the liver reduces blood NEFA and BHB levels, creating a positive impact on the immune function.

Feeding a blend of protected B vitamins (folic acid, choline and riboflavin) increased prepartum dry matter intake, reduced blood BHB levels and the incidence of infectious diseases, such as mastitis and metritis.

Oxidative stress, which has a negative impact on immune system and reproduction, is increased during the transition period. Riboflavin, another B vitamin, is involved in the reduction of the oxidative stress by being the cofactor of an important enzyme. Riboflavin also plays an important role in the activation of immune cells destroying bacteria (neutrophils).

Negative energy balance and its resultant factors will delay the resumption of ovarian activity. A nutrigenomic study revealed that supplementation of folic acid and vitamin B12 during the transition period improved development of the dominant follicle toward the ovulation process. This may be related to the positive effects of these B vitamins on energetic efficiency.

Protected* B vitamins are an innovative tool to improve the health of your cows during their transition period. Healthier cows leads to increased milk production and improved reproduction, which represents substantial economic gains for your farm.  PD

*Microencapsulated to prevent ruminal degradation of the B vitamins.

References omitted due to space but are available upon request. Click here to email an editor.

Protected B vitamins are an innovative tool to improve the health of your cows during their transition period. Healthier cows leads to increased milk production and improved reproduction, which represents substantial economic gains for your farm. Photo courtesy of PD staff.

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Hélène Leclerc MSc.
Technical Support and R&D