Researchers from Cornell University and the University of Wisconsin recently published results from a field trial looking at the effects of propylene glycol on milk yield and resolution of ketosis in fresh cows diagnosed with subclinical ketosis in the Journal of Dairy Science. This was a large trial conducted on four commercial dairies in New York and Wisconsin. As such, the results may relate better to the real situations encountered on dairies than the results of smaller trials conducted under controlled research conditions.
Farms ranged in size from 1,800 cows to 4,100 cows. Data was collected for 1,717 cows for the first 16 days in milk for the presence of ketosis. Blood beta-hydroxybutyrate (BHBA) levels were used to define subclinical and clinical ketosis status (1.2 to 2.9 mM per L and greater than 3.0 mM per L, respectively).
The trial concluded that oral application of liquid propylene glycol to treat cows with subclinical ketosis reduced the chances of cows progressing to clinical ketosis by about 50 percent. Subclinical ketotic cows treated with propylene glycol were 1.5 times more likely to resolve their subclinical ketosis within two weeks of calving than subclinical ketotic cows that did not receive propylene glycol.
In two of three herds with daily milk weights for individual cows, subclinical ketotic cows treated with propylene glycol produced about 3 and 3.5 pounds more milk per day for the first 30 days in milk than subclinical ketotic cows that were not treated with propylene glycol. There was no effect on milk production in the third herd.
None of these results should surprise anyone.
This new trial did an excellent job of pointing out a number of very key and critical points about subclinical ketosis (and fresh cow metabolic problems in general).
First and foremost, the incidence of subclinical disease is much greater than clinical disease. Remember, subclinical means you cannot see the symptoms. You only know it is occurring based on a diagnostic test.
In this trial, the incidence of subclinical ketosis was 43.2 percent of cows, compared to a clinical ketosis incidence of 8 percent, during the first 16 days in milk. Subclinical ketosis incidence in individual herds ranged from about 26 percent to 55 percent. This confirms many previous studies in which subclinical ketosis incidence is quite variable but averages more than 40 percent across all studies.
Bottom line â subclinical ketosis is a huge problem, and this study confirms it yet again.
Second, researchers in this trial utilized a quantitative, cowside blood test for ketosis. The Precision Xtra is a hand-held meter that measures beta-hydroxybutyrate (BHBA) from about one drop of blood, usually taken from the tail vein. This test is very accurate, relatively inexpensive and provides immediate results.
You may want to discuss with your veterinarian how this tool might help you with early identification of ketosis and how results may fit into making decisions about your fresh cow management program.
Third, results from two of three herds showed a sizeable increase in milk production by early intervention of subclinical ketosis. This is important for two reasons. Early intervention almost always gives the best outcomes for disease treatment. Also, most dairymen do not realize the amount of milk they lose due to subclinical ketosis.
For this trial, if we average the two herds that showed improved milk and the herd that showed no improvement (2.95, 3.5 and 0.04 pounds, respectively), when subclinical ketotic cows were treated with propylene glycol, we get an average improvement of 2.16 pounds per cow per day.
If we multiply this production advantage by the incidence of subclinical ketosis, this trial would indicate that subclinical ketosis costs dairy producers about one pound of milk per cow per day, or 300 pounds per lactation for all cows.
While it is not exactly accurate to assume that healthy cows without any subclinical ketosis would produce this same amount of additional milk, it may give us a conservative estimate of what subclinical ketosis costs on average, at least for the first 30 days.
Other research indicates that the negative effect of subclinical ketosis on milk production is larger, and these effects probably last for the entire lactation.
Please note that this trial did not examine the use of propylene glycol on a prophylactic basis, only as a treatment of subclinical ketosis once it was identified. Daily feeding of propylene glycol during the late dry period, calving and early postpartum period has yielded mixed results for both control of ketosis and milk production in other studies.
The objective with any prophylactic program for ketosis is to improve blood glucose levels in early-lactation cows. The most efficient liver pathway by which cows synthesize blood glucose utilizes the volatile fatty acid propionate, which is produced by rumen microbes.
Propylene glycol can enter this pathway and serve as a glucose precursor. Unfortunately, when propylene glycol is fed to cows for more than a few days, rumen microbes turn on their own metabolic pathways to utilize much of the propylene glycol before it can be absorbed into the blood stream.
Short-term oral use of propylene glycol on ketotic cows has been a long-standing and effective treatment protocol. This study shows it also gives a response in cows with subclinical ketosis.
Longer-term management strategies should revolve around improving the propionate supply to the liver. Enhancing the rumen microbial yield of propionate has shown to be very effective.
In my opinion, the most remarkable information produced by this trial is the high incidence of subclinical ketosis. Dairymen should consider subclinical ketosis and subclinical hypocalcemia (milk fever), as the two biggest issues affecting their fresh cows.
Numerous studies have now shown the incidence rates of each of these two profit-stealing conditions to be more than 40 percent of all cows that calve. And, it is not the same cows always getting both.
Fresh cow management programs that specifically target subclinical ketosis and hypocalcemia are warranted in all herds at all times regardless of milk prices. These programs should focus on increasing rumen microbial propionate yield (and subsequent blood glucose levels) during both the prepartum and postpartum period, and improving blood calcium levels on calving day.
When milk prices are high, fresh cow programs provide an excellent return from milk sales throughout the entire lactation. When milk prices are low, fresh cow programs save dairymen from huge losses in treatment costs associated with clinical ketosis and clinical hypocalcemia (and subsequent diseases for which these are known risk factors), lost production and decreased reproductive efficiency. PD
Zimmer is also president of Bio-Vet Inc. , based out of Blue Mounds, Wisconsin.