A cow’s dry matter intake is low post-calving. The increased energy demand of lactation outpaces the energy she is consuming, consequently pushing her into a negative energy balance. To meet these energy demands, cows will mobilize fat tissue. This is a normal and natural process that nearly all cows go through in early lactation.
    The problem arises when a cow is forced to mobilize too much body fat to meet energy demands, resulting in more fat entering the liver than can be effectively and completely metabolized. This leads to the formation of ketone bodies which circulate in the bloodstream.
    Subclinical ketosis is defined as increased levels of circulating ketone bodies without the presence of clinical signs of ketosis. Most dairy producers would agree that the cost of subclinical disorders can often be greater than clinical cases. Unlike clinical ketosis, subclinical ketosis cannot be diagnosed by outward signs. These cows can easily go undetected and untreated unless blood, milk or urine tests are conducted.
    Subclinical ketosis has been associated with decreased milk production, reduced reproductive performance, displaced abomasum, metritis, mastitis and clinical ketosis. The economic ramifications of subclinical ketosis can be enormous. Canadian research in 2002 estimated each case of subclinical ketosis costs a farm about $78.
    Research suggests that 30-50% of herds have subclinical ketosis in more than 15% of their fresh cows. The highest prevalence of subclinical ketosis is in the first two months post-calving with the greatest risk in the first two weeks. Cornell research showed the greatest incidence of subclinical ketosis at five days in milk. Most herds screening for subclinical ketosis will focus on cows four to 12 DIM.
    Traditional measurements for subclinical ketosis are based on a simple chemical reaction that takes place when using milk ketone powder and urine ketone paper strips. While these are common cow-side tests, samples may be difficult to obtain. In addition, lack of sensitivity makes them less-than-desirable tests.
    Blood sampling is considered the gold standard for subclinical ketosis measurements. One of the ketone bodies that is most easily measured is beta-hydroxybutyric acid (BHBA). Sending blood samples to the lab for BHBA analysis is costly and time-consuming with results generally too late to take individual cow action. Fortunately, we now have cow-side meters capable of measuring blood BHBA within 10 seconds.
    Meters originate from the human health industry and can measure glucose and BHBA. For fresh cows, it is recommended to purchase the BHBA ketosis strips. Two common meters on the market are Nova Max® and Nova Vet™.
    Results with these meters will be expressed in units of millimole per liter. Cows with blood BHBA concentrations from between 1.2 to 3 mmol/L are in the zone for subclinical ketosis. Readings over 3 mmol/L are generally considered clinical ketosis.
    It is important to point out that higher-producing cows typically have higher levels of blood ketones than lower-producing dairy cows. This only makes sense. Higher-producing cows mobilize more body fat and are at a higher risk of developing subclinical ketosis.
    Slightly elevated BHBA values are not always an indicator for subclinical ketosis and fresh cow health problems. If cows are milking very well but testing above the alarm level, observation may be all that is necessary. Assessing appetite, attitude, production and health records can be valuable in determining the course of action.
    Cow-side BHBA meters can be a valuable tool to identify subclinical ketosis incidence and prevalence within your herd. Meters can be used on an individual cow basis or as part of a herd monitoring system. Work with your veterinarian and herd health team to develop treatment protocols using blood BHBA results.
    Barry Visser is a nutritionist for Vita Plus.