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Every dairy cow goes through a state of negative energy balance (NEB) somewhere between late gestation and early lactation. Most cows will be able to manage NEB just fine, but there will always be some that will experience excessive NEB. Those cows are at risk for a host of problems, such as metabolic and infectious diseases, decreased reproductive performance, and reduced milk production. In short, the problems stem from increased mobilization of fats, or lipids, from body tissues. Lipid mobilization happens because of an increased demand for glucose to support the onset of lactation, and because of reduced dry matter intake (Sordillo, 2013). Lower blood glucose results in a decrease in blood insulin. Lower insulin levels trigger the release of nonesterified fatty acids (NEFA) from adipose (fat) tissues.
Normally, NEFAs are used as a source of energy to spare glucose, but when lipid mobilization is very rapid, NEFAs may accumulate and result in a variety of negative effects, including: oxidative stress and uncontrolled inflammatory responses, subclinical or clinical ketosis, fatty liver disease, displaced abomasum, endometritis, and a reduced immune response. Suppression of the immune system may lead to a variety of infectious diseases including mastitis, metritis, pneumonia, sepsis, or others. Simply put, many of these cows just crash. Identifying problem cows early can allow dairy producers to treat affected animals to prevent some of the negative downstream effects of disease, and also can serve as a monitor for transition cow management, allowing one to make changes in the system to hopefully reduce the incidence of excessive NEB and subsequent disease.
The simplest way to identify affected cows is to test their blood or milk for ketone bodies. The best tests are blood BHBA, measured with the Precision Xtra meter, or milk with either the Ketotest or PortaBHB tests. Urine testing is also useful using the Ketostix strips at the trace level, but one must read the test immediately after urine is applied, and of course, not all cows will urinate when prompted to do so. Powder tests used on milk are not an acceptable way to screen for ketosis due to low test sensitivity.
Recently a testing scheme has been proposed (Opsina, 2013) for herds with higher than expected incidence of transition cow diseases. The purpose of testing is to estimate the prevalence of subclinical ketosis, and then to institute prevention and treatment interventions accordingly. The steps are as follows.
1. Sample approximately 20 cows that are three to 14 DIM. Positive cows are over 1.2 mmol/L (read as 0.12 on the Precision Xtra) BHBA in blood.
2. Calculate the percent positive.
3. If 15 percent or less are positive, it is appropriate to continue to monitor by testing every other week.
4. If more than 15 percent but less than 40 percent are positive, more intensive monitoring, with treatment of high cows, is indicated. All cows should be tested between three and nine DIM twice a week. Positive cows should be treated with 300 ml of propylene glycol orally for five days. If levels of positive cows drop below 15 percent for two consecutive weeks, one can go back to monitoring prevalence every two weeks.
5. If greater than 40 percent of cows are positive, it makes economic sense to treat all cows daily with propylene glycol for five days starting at three DIM. Testing should be repeated in a couple of weeks.
Herds with a normal or expected incidence of transition cow diseases may benefit from checking BHB levels between three and 14 DIM at a frequency ranging from biweekly to every other week. Herds that have a high level of transition cow disease, but that do not have a high prevalence of subclinical ketosis (high BHB) postpartum may benefit from testing for excess levels of nonesterified fatty acids (NEFA) in the blood. This testing is somewhat more difficult and more expensive than BHB testing, however.
Another monitoring tool are the variety of transition cow reports available, mostly through DHI testing centers or on-farm software. Lately a new report is being offered by Zoetis that includes the Transition Cow Index (TCI) that was developed at the University of Wisconsin. The TCI score in the Zoetis report is listed in pounds of milk expected, per cow, more or less than observed. These sorts of reports can be valuable monitoring tools, but they do not define the problem to the cow level like individual BHB testing is able to do.
Treatment of affected cows with propylene glycol is the most reliable treatment option. There are a variety of other treatments that also may be of use; specifics should be at the recommendation of the herd veterinarian. Of course, the ideal solution is to identify the reason or reasons why cows experience severe NEB. The investigation may require blood testing of prefresh cows for excess BHB or NEFA to determine when negative energy balance is occurring. Typical causes are overcrowding or inadequate feeding space in the prefresh pen, excessively over conditioned cows, lack of heat abatement in prefresh and post fresh cows, excessive pen moves, excessive energy or unbalanced protein in diets, or other stressors of prefresh and dry cows that may result in lowered dry matter intake. Sometimes the fix is not easy, but it is pretty clear that the effects of NEB can be very detrimental to the cow and very expensive for the dairy producer.
Furthermore, as we go into the future, cows will produce more milk, thus the change from a state on non-lactation to one of lactation will be of greater magnitude and speed, making NEB more likely, and thus the risks of excess NEB greater. Thus, without intervention, diseases of transition will become more common and likely in the future. BHB testing of fresh cows can help identify errors in transition management and can identify specific cows in need of interventions.
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