If you've been in the dairy business for more than a few years, you've most likely tangled with the metabolic disorder called ketosis.
Ketosis occurs in dairy cows when there are high levels of ketone bodies circulating in their bloodstream. When dietary energy precursors for glucose are in limited supply in early lactation, the cow begins metabolizing fat. The liver has a limited capacity to process fatty acids, and if a cow is in an extreme level of negative energy balance and forced to mobilize large amounts of body fat at a rapid rate, fatty liver syndrome develops and the liver leaves parts of the fatty acids in fragments called ketone bodies. These ketone bodies find their way into the bloodstream, further limiting glucose metabolism and making the cow ill.
Ketosis occurs primarily in the days immediately after calving, when a cow's milk production requires a rapid increase in energy metabolism that cannot be met by feed intake alone. Remember, a cow's feed intake lags behind her nutritional requirements for milk production immediately after freshening.
Ketosis can occur in both thin and over-conditioned cows. The severity of ketosis in a cow can vary; it can cause minor disruptions to health and milk production, or it can leave cows too sick to eat, resulting in displaced abomasums (DA). If left untreated, death will occur due to insufficient nutrient intake.
A paper presented at the 2012 Cornell Nutrition Conference stated that in a study involving 1,717 fresh cows, the incidence of subclinical ketosis (SCK) averaged 43.2 percent. Earlier studies also found that SCK averaged from 40 to 60 percent. In other words, nearly half of all fresh cows can be expected to have SCK to some degree. The same study showed that the peak incidence of SCK occurred at only five days after freshening.
The treatment of choice for both clinical and SCK is dosing with propylene glycol. The recommendation for treatment is 300 milliliters orally once daily until the ketosis is resolved. Due to the fact that SCK is so prevalent and likely to occur, it may be a good management strategy to drench cows with propylene glycol as a prophylactic at the time of freshening.
For many years, the accepted means of testing for ketosis was the chemically treated keto-strip, on which a cow must urinate. The chemical on the strip would turn a shade of purple in the presence of ketone bodies. In recent years, through the wonder of computer technology, a hand-held electronic meter can precisely test blood for the presence of one particular ketone body. A small amount of blood is placed on a test strip, read electronically and converted into a reading on the meter, which indicates the level of beta-hydroxybutyric acid (BHBA) in the blood. A meter reading of 1.2 millimoles per liter (mmol/L) is considered the lower limit indicating SCK. Values below 1.2 tell us the cow is not ketotic. A reading of 3 mmol/L or greater is considered to indicate clinical ketosis and cows should be treated immediately.
Signs of clinical ketosis are decreased appetite, decreased milk production and weight loss. As a cow mobilizes more body fat to compensate for the energy deficiency in the diet, the problem worsens, producing even more ketone bodies, causing the condition to spiral out of control.
There is now an abundance of research showing that BHBA levels elevate rapidly during negative energy balance of a fresh cow, and there is a very positive correlation of decreased milk production in the BHBA range of 1.2 to 2.9 mmol/L. For each additional .1 increase of BHBA, there is a drop of 1.1 pounds of milk during the first 30 days of lactation.
Along with the increased chances of a DA in early lactation, there is also evidence that ketosis can have a negative effect on immune function, leading to metritis, an infection in the uterus. Some studies have been done looking to link ketosis and impaired fertility, but the results are inconsistent. It is known, however, that cows that are treated with propylene glycol have an increased chance of conception at first insemination, suggesting that there is an indirect correlation between reducing ketone bodies and improved conception.
As the saying goes, "a stitch in time saves nine." Ideally, we would like to prevent both SCK and clinical ketosis in all of our dairy cows. However, the metabolism of the modern, high-producing dairy cow makes some level of ketosis inevitable. As already noted, nearly half of all cows in modern dairy herds can be expected to have a case of SCK.
Maintaining ample energy density in far-off and close-up dry cowdiets, along with keeping them on a solid and consistent plane of nutrition, are the first and most effective ways to minimize SCK in fresh cows. More dietary energy available to the cow means she will metabolize less fat off of her back and keep the BHBA levels to a minimum. Net energy for lactation (NEL) should be between .65 and .70 megacalories per pound of dry matter. This nearly always requires some addition of cornmeal and/or rumen-protected fat in the diets. Proper close-up cow management must be in place to encourage dry matter intakes right up to the last few days before calving so that the rumen remains active and healthy.
Ketosis and fatty liver syndrome go hand in hand in the fresh dairy cow. The process of converting fatty acids to glucose is somewhat complex, and the liver can quickly become overloaded with fat. Many studies have determined that the organic compound choline (often called a vitamin) plays an important role in the fat-to-glucose conversion. Choline is synthesized in the cow's body, but not enough to ward off severe cases of fatty liver. In order to be effective as a means of reducing fatty liver and BHBA, choline must be fed in a rumen-protected form.
One company, Balchem Corp. (www.balchem.com), offers a rumen-protected choline product (RPC) that helps the liver convert fatty acids to glucose, thereby reducing the accumulation of ketone bodies. The inclusion of an RPC in close-up diets has been shown to reduce ketosis and improve health and milk production. It's recommended that about 15 grams of an RPC be fed to transition cows from 25 days before freshening to 80 days after freshening.
Even low levels of SCK will have an economic impact on dairy cows, estimated to range between $50 and $100 during a lactation. With the high levels of SCK now known to exist in modern dairy herds, SCK is without a doubt a costly and profit-robbing metabolic challenge when left undetected or poorly managed. The prevention and/or reduction of ketosis is fairly straightforward and represents an economic opportunity in many dairy herds.
The author is a vegetable and berry specialist with University of Vermont Extension based at the Brattleboro office.