What is the incidence of subclinical ketosis in early lactation cows? What is the bottom line effect of that health problem? Is there a nutritional way to reduce the number of subclinical ketosis cases?
Those questions were examined in a Dairy Herd Network webinar by Garrett Oetzel of the School of Veterinary Medicine at the University of Wisconsin-Madison and by Balchem Corp. ruminant technology director Ric Grummer, who was the director of the department of dairy science at UW-Madison from 2004 to 2010.
Clinical and subclinical ketosis are two of the downside "remarkable metabolic shifts" that dairy cows undergo as a result of calving, Oetzel noted.
The list of metabolic disorders is due to the rapid change from a positive to a negative energy balance in the cows, he pointed out.
Within that spectrum, of which subclinical ketosis was the focus of the webinar, ketosis is linked to the flow of ketone bodies that originate with fatty livers, Oetzel explained.
The signs of subclinical ketosis are a loss of appetite, which shifts toward dry hay and away from haylage and corn silage, noticeable weight loss, cutback in milk production, and a dull appearance in the cow, he remarked.
Oetzel indicated that such observations are much easier in smaller dairy herds than in free-stall operations. He said the diagnosis can be subjective and that subclinical ketosis does not involve an abnormal body temperature.
In a more precise manner, the methods of verification of subclinical ketosis are a urine or milk test or a fairly simple blood test, Oetzel stated.
He said the Precision Xtra blood test, available from Abbott Laboratories, involves taking a drop of blood from the tail and getting a reading on test strip (cost about $1.50) in about 10 seconds.
A meter required for taking that test costs between $10 and $80, Oetzel added. He suggested obtaining the test strips through the dairy herd veterinarian but noted that a back-order problem exists at the moment.
study looks at frequency of subclinical ketosis
Oetzel described three degrees of ketonemia, which are based on numerical readings - millimolars per liter - in the blood samples.
The middle or subclinical range of those three degrees generally appears at three to 16 days into a lactation with total mixed ration feeding and at between 15 and 50 days with component feeding at individual feeding sites for cows, he said.
He attributed the timetable difference to the competition for feed that occurs in group feeding settings.
Depending on the herd size, the incidence of subclinical ketosis could be calculated at a monthly or annual rate, Oetzel stated. He said the ideal would be to test twice a week but conceded this is not practical in many cases.
He also pointed out that less frequent testing could miss 40 to 60 percent of the actual total because many cases resolve themselves in about five days.
To get a better handle on the frequency of subclinical ketosis, Cornell University led a study in four commercial dairy herds - two in New York and two in Wisconsin - that was conducted in 2010.
The results were published earlier this year, Oetzel reported. That study allowed for intense testing - three days per week or a total of six tests per cow until day 14 to 16 of the new lactation.
This study involved herds with a total of 1,717 cows. The herd sizes were 354 and 402 head in New York and 291 and 670 in Wisconsin.
The respective percentages of cases of subclinical ketosis in those herds were 46.4, 26.4, 40.9, and 55.7. This put the average at 43.2 percent - a number close to the 40 percent average that Oetzel believes is accurate across most dairy herds.
The Cornell study identified day five into a lactation as the most frequent for an outbreak of subclinical ketosis, followed by day seven.
Oetzel believes the amount of milk loss caused by subclinical ketosis is underestimated, noting that the ailment is more likely to strike the highest-producing cows.
He cited five studies, which tabulated milk losses of between 3.4 and 7 percent and indicated that the milk loss increases if subclinical ketosis strikes early in the lactation.
Oetzel also noted that every .1 increase in the blood test on the subclinical scale from 1.2 to 2.9 millimolars correlates to one more pound of milk loss per day.
The most severe cases of ketosis are also significantly more likely to be associated with displaced abomasum and perhaps with metritis, Oetzel continued.
He said that dosing transition cows with propylene glycol tends to help limit the outbreak or severity of ketosis about 50 percent of the time.
Regarding conception rates following a bout of ketosis, Oetzel said the research results are inconsistent.
He said a study in Canada indicated conception rates that were 27-40 percent lower but noted this has not been replicated in other formal research, most likely because some or all of the cows involved were placed in an OvSynch breeding program.
For the economic effects of ketosis, Oetzel mentioned amounts of $46, $68, and $92 per case along with a major study showing losses of $33 to $109 per case or an average of $67.
At a subclinical ketosis rate of 40 percent of early lactation cows, he said a dairy herd would suffer an economic loss of about $30 per cow per lactation.
Addressing the fatty liver syndrome
To address the fatty liver syndrome, which leads to the outbreak of ketosis, Oetzel suggests reducing the social stress (number of movements between cow groups or to new locations) in the weeks before calving.
He also recommended avoiding overconditioning (too high a body condition score) during the dry period, proper nutrition, at least 30 inches of bunk space per cow, and supplementing with monensin and choline.
Ric Grummer described choline as a quasi vitamin. Other sources indicate that it is a close relative of the vitamin B complex and is a nutrient that is essential for cell membrane, muscle, and overall body function, including in humans.
Choline draws fat from the liver in the form of low density lipoprotein, Grummer indicated.
He cited studies from around the world that show 50 percent of fresh cows have a moderate to severe fatty liver, which is defined as having five or more percent fat on a liquid basis.
Any such existing condition is exacerbated by the fact that the liver will take up about 13 times more fatty acids at calving, Grummer explained.
He said this continues for up to two to three months - a phenomenon that can be observed as early lactation cows shed fat from their backs.
The calving day reactions can add one pound of fat to a cow's liver and the back fat can deliver another 10-12 pounds in the following days and weeks, Grummer pointed out.
To counteract that, he prescribes choline because cows produce very little of it naturally nor do they obtain much of it in their ordinary nutritional intake.
To be effective and palatable, choline needs to provided in a protected form and either top-dressed (individual cow feeding) or included in a ration's mineral mix rather than not being added until all of a mixed ration's components are combined, Grummer emphasized.
He recommends a daily dose of 15 grams of choline per day, which converts to about 60 grams of actual product because of the coating.
The choline should be provided to transition cows from three weeks before the projected calving date to three weeks afterward, Grummer advised.
In the past, he indicated, it has been supplemented in a targeted manner but he prefers that it be provided to all cows as they approach their transition period to a new lactation.
Grummer described the technical biological processes, which link the excess of liver fat to loss of milk production and other metabolic problems ordinarily associated with calving and the start of a lactation.
A University of California-Davis study also suggested a reduction of mastitis cases if the problems stemming from fatty liver are controlled, he added.
A compilation of 13 studies of transition cows showed average daily improvements of 1.6 pounds of dry matter intake and 4.9 pounds of milk production if 12-15 grams of choline are provided per day and the severity of ketosis is reduced, Grummer reported.
He said methionine can provide the same benefits and is valuable on its own in other ways but noted that methionine would have to be supplemented at a rate of 4.3 grams for every gram of effective choline in order to have the same effect.
Replying to a webinar listener's question, Oetzel said the incidence of subclinical ketosis has probably increased slightly over time but noted that this has not been carefully documented.
He indicated that management changes, which introduce some of the conditions that lead to fatty liver are a contributing factor.