Subclinical ketosis (SCK) is having a tremendous negative impact on our dairy cows, according to a recent presentation at the Cornell Nutrition Conference by Dr. Oetzel from the University of Wisconsin’s School of Veterinary Medicine. By definition, SCK is an excess of circulating ketone bodies in the blood without clinical signs of ketosis (i.e. decreased appetite, weight loss, and decreased milk production). The lack of clinical signs makes it difficult to detect SCK. However, using blood beta-hydroxybutyrate (BHBA: a ketone body) testing to measure the incidence or prevalence of SCK in a herd is a powerful and useful clinical tool. The blood measurement can be made on-farm with a handheld Precision Xtra meter or blood can be sent to a lab for analysis.
The lower threshold concentration of BHBA for SCK is 1.2 mmol/L or 12.4 mg/dL. Multiplying the BHBA concentration expressed as mmol/L by 10.3 converts it to mg/dL. The upper threshold of SCK is 3.0 mmol/L or 30.9 mg/dL. However, the upper threshold is somewhat arbitrary or subjective and is really when clinical signs become evident. Based on Dr. Oetzel’s clinical experience, he finds that producers with larger herds tend to underestimate the incidence of ketosis. In contrast, producers with smaller herds (i.e. tiestalls) overestimate the incidence of ketosis because they can observe individual intakes. The incidence of SCK in a herd is the number of new cases of SCK (defined as blood BHBA between 1.2 and 2.9 mmol/L) during a risk period divided by the number of cows who completed the risk period. The risk period can be defined as a week, a month, or a year. Most new cases of SCK occur within the first 2 or 3 weeks after calving in herds that manage cows in groups and feed a TMR. Determining the incidence of SCK requires repeated testing (i.e. 2 or 3 times per week) of cows during the risk period since the median time for the resolution of SCK is about 5 days. In a large field study with 4 well-managed herds, the SCK incidence ranged from 26 to 56% with peak incidence occurring at 5 DIM!
Another way to evaluate the occurrence of SCK on herds is to look at prevalence. This is a “snapshot” measure of the current SCK status of a group of cows. It is defined as the proportion of cows with blood BHBA between 1.2 and 2.9 mmol/L at a given time point. Cows are not repeatedly tested. The incidence of SCK is reported to be 2.2 to 2.4 X the prevalence. In the large field study mentioned previously, the peak prevalence of SCK occurred at 5 DIM underscoring the observation that SCK occurs very soon after calving.
There are several negative impacts of SCK that result in an estimated economic loss of $46 to $92 per case.
Reduced milk yield (3-7%): the severity of milk loss to SCK was associated with BHBA concentration and DIM at the first SCK diagnosis.
Each 0.1 mmol/L increase in BHBA above 1.2 mmol/L was associated with 1.1 lb more lost milk for the 1st 30 DIM.
Cows diagnosed between 3 and 7 DIM produced less daily milk (6%) than cows diagnosed between 8 to 16 DIM in the 1st 30 DIM.
Increased risk for herd removal (sold or died)
Cows with SCK were 3 X more likely to be removed.
Each 0.1 mmol/L increase in BHBA above 1.2 mmol/L increased the risk for herd removal by 1.4 X.
Increased risk for displaced abomasum (DA)
Each 0.1 mmol/L increase in BHBA above 1.2 mmol/L increased the risk by 1.1 X.
Cows diagnosed between 3 and 5 DIM were 6.1 X more likely to develop a DA than cows diagnosed between 6 to 16 DIM.
Impaired fertility in some situations
Cows diagnosed between 3 and 7 DIM were 0.7 X as likely to conceive at 1st service as cows diagnosed between 8 to 16 DIM
Ovulation synchronization programs may mask the effects of SCK on fertility since it overcomes failure to cycle and poor estrus detection.
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