animal care and health

by Mark J. Thomas, D.V.M.
The author is a dairy practitioner and owner/partner in Countryside Veterinary Clinic, Lowville, N.Y.

When a cow's intake of energy does not meet her energy needs for maintenance and milk production, she begins to burn fat as an energy source.

One common form of ketosis (Type I) occurs when a cow is in negative energy balance. She is not consuming enough energy to meet her metabolic needs. This generally occurs in early lactation when the cow's feed intake is unable to keep up with climbing milk production.

When a cow's intake of energy does not meet her energy needs, she begins to burn fat as an energy source. The liver is the necessary organ to convert fat into usable energy (sugar). Think of the liver as a factory with an output limit. It can only convert so much fat into sugar. Once this pathway is overwhelmed, the liver produces ketones. Ketones can be used as an energy source, but they are much less efficient, and they cause the cow to feel sick. This becomes a downward spiral . . . the cow does not feel well, eats less, burns more fat, and makes more ketones. She now has clinical ketosis.

Two other forms of ketosis can occur as a result of either "fat cow syndrome" or the consumption of forages high in butyric acid. "Fat cow" (or Type II) ketosis occurs when dry matter intake declines before freshening. This most commonly occurs in overconditioned cows but can also occur when dry matter intake is restricted to cows prior to freshening. This often is the result of overcrowding or improperly balanced prefresh rations. Cows with Type II ketosis are very difficult to manage and don't respond well to treatment.

Butyric acid-induced ketosis is caused by the direct consumption of ketones in the diet. This causes poor dry matter intake and the obvious downward spiral as seen in Type I ketosis.

All cows affected
Our ability to provide cows with unlimited access to a well-balanced ration and free them from any obstructions to normal behavior (good stall design, flooring, minimize social stresses, and so forth) will aid in reducing incidence of ketosis. But we must recognize that all high-producing cows are in some level of negative energy balance in early lactation and, therefore, must use body reserves (burn fat) for energy.

Just like other diseases, such as mastitis, a cow can have subclinical or clinical ketosis. A cow with subclinical ketosis generally appears normal but has elevated levels of ketones in her blood. We know from research that cows with subclinical ketosis are more likely to get a displaced abomasum, less likely to get pregnant on time, and will produce less milk. These cows also are more likely to progress to clinical ketosis.

So, if research supports the fact that subclinical cows are negatively affected long term and more likely to get a DA, can we really call it subclinical disease? Perhaps we need to retrain ourselves to detect these cows before they become clinical and suffer more severe disease. So, how do we find ketotic cows?

Traditionally, we have used the urine dipstick to detect the presence of ketosis. Some people also are very sensitive to the odor of ketones and can detect them by smelling the cow's breath (or even their milk). The urine dipstick is an easy and inexpensive test but is not very accurate. This means that the level of color change may not give an accurate estimate of the level of blood ketones. In cases where cows are routinely checked using the urine ketone test, it is important to also evaluate the cow clinically.

Remember to first do no harm. Administering a bottle of dextrose intravenously may seem like an easy procedure, but how stressful is this on the cow? It also actually may be detrimental to cows with Type II ketosis. We really do not know, but overtreatment may be a concern in some herds. If the cow is bright, alert, eating, has a full rumen, and a full udder but is ketotic, should we treat her? Remember, some degree of ketone production is normal in early lactation.

So, how can we determine which cows to treat? Having a more objective measure of blood ketone levels has provided the opportunity to help retrain both veterinarians and herdspeople to the levels of concern. Over the past few years, the use of the Precision Xtra blood ketone (betahydroxybuterate-BHBA) meter has given us a method to quickly and accurately determine blood ketone levels cowside.

Through a number of on-farm trials with dairy producers and herdspeople, we have found that the sensitivity of the Precision Xtra meter is far greater than the urine dipstick. University trials also have shown that the meter provides accurate values as compared to standard laboratory testing for BHBA.

Given that the meter only requires a single drop of blood, it is a quick and easy procedure. Generally, we only use a needle prick to the tail vein with a 20g x 1-inch needle. The syringe usually is unnecessary as you can quickly obtain a drop of blood without the use of a syringe. After placing the drop of blood on the test strip, the meter will give a result in 10 seconds.

The Precision Xtra meter costs between $15 and $20, and the test strips are available for about $1.30 per strip through all the major veterinary distributors. This cost is considerably lower than the past when the strips were available only through human distributors.

At $1.30 per test, this is an economic method to help identify cases of ketosis. More dairies now are utilizing this meter as a tool to fine-tune the treatment protocol based on an accurate value for blood ketones. The meter also has enabled us to find the "subclinical" cow that often was overlooked.

Get herd perspective
Another practical use for the Precision meter is herd-based sampling. Commonly, we sample 12 to 15 healthy fresh cows (about 5 to 25 days in milk). If more than 15 to 20 percent (2 to 3 of the 12 to 15) sampled cows have BHBA levels greater than 1.2 millimoles/liter (mmol/L) on the meter, we know that the level of negative energy balance is affecting herd health and production.

Research conducted by Daryl Nydam and his colleagues at Cornell University has shown that herds that have greater than 15 percent of sampled cows with a BHBA level greater than 1.2 mmol/L (12 mg/dL) have a 1.8 percent greater incidence of displaced abomasum and clinical ketosis, a 0.8 percent lower in pregnancy rate, and a decline of 1,175 pounds and 790 pounds of mature-equivalent milk for heifers and adult cows, respectively.

If we relate these percentages to dollars, this can represent a loss of over $13,000 for every 100 cows ($2,000 for the greater incidence of displaced abomasum and ketosis, $1,200 for the decline in pregnancy rate, and $10,000 for the loss in milk production).

The bottom line is that ketosis is a costly disease, and we must improve all aspects of nutrition and management to both the dry and transition cow to reduce the incidence. By using new technologies and philosophies for ketosis identification and treatment, we likely can have a positive impact on overall herd performance and animal welfare.

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