Preventing Milk Fever: DCAD Balancing for Prefresh Cows

by Steve Echelmeier, Regional Sales Manager, Idaho

The dairy industry has suffered the consequences of milk fever in transition cows for decades, thus resulting in countless research trials performed to help minimize the number of cases of the metabolic disorder. However, despite our improved understanding of the causes and remedies for milk fever, it remains to be a problem that is far from being eliminated. It is estimated that 5-10% of fresh cows fall victim to the disorder, costing the producer hundreds of dollars per incident. It may also lead to other health disorders such as ketosis, retained placenta, uterine prolapse, decreased rumen motility, and displaced abomasum, resulting in lost milk and possible loss of the animal.

Though it may never be completely eliminated in the industry, rest assured that it can be virtually non-existent on your dairy when the proper steps are taken with your prefresh cows.

It has been well-understood that milk fever is caused by low blood-calcium (Ca) levels just before calving as large amounts of calcium are being utilized for milk production.

Furthermore, a healthy animal must maintain a neutral or slightly negative balance of anions (primarily Chloride and Sulfur) and cations (primarily Sodium and Potassium) in the body in order to negate low blood Ca. Therefore, the dietary cation-anion difference (DCAD) must be calculated and monitored to maintain the desired level. The accepted formula for DCAD calculation is as follows:

[(% sodium/0.023) + (% potassium/0.039)] − [(% chloride/0.0355) + (% sulfur/0.016)]

Strategies to control the DCAD include feeding low potassium (K) forages along with a highly palatable ration to encourage intakes or feeding low K forages as well as anionic supplements along with a very palatable ration. Focusing on low K forages will bring the DCAD to a near zero balance, while adding anionics will bring the DCAD below zero. Davidson et al. (1995) recommended a DCAD of -10 to -15 milliequivalents per 100 g dry matter for close-up dry cows. Horst et al. (1997) summarized six studies involving anionic salts and concluded that milk fever prevention is highest when DCAD is -5 to -10 milliequivalents per 100 g dry matter. There have been no documented benefits from going lower than -15 DCAD or for feeding such a ration for longer than 21 days pre-calving. In fact, it may be detrimental to intakes by going lower or feeding longer, as anionic salts are often viewed as unpalatable and have been associated with depressed intakes in the prefresh pen. (Note that when feeding anionic supplements, dietary Ca is recommended to be increased to 1.5% and Magnesium to 0.5% of the prefresh ration.)

The accepted method of monitoring DCAD effectiveness and cow health prior to calving and prior to clinical milk fever occurrences is by weekly testing of urine pH. After a week of feeding anionic salts, monitor the urine pH of 12 to 15 prefresh cows at 4 to 6 hours after feeding. If urine pH is above 7.0, more anionic salts can be added. If pH is 6.5 to 5.5 and dry matter intake is acceptable, then continue with the current diet. However, if urine pH is less than 5.5 or dry matter intake has significantly declined, remove some of the anionic salts.

Three additional points of perhaps even more importance to remember:

• You must frequently test and monitor feedstuffs for macro minerals through wet chemistry analysis. Forages may change across seasons and fields, therefore know what you have before adding an anionic package to the prefresh ration.
• Eliminate sorting as much as possible by processing forages thoroughly and maintaining a maximum of 50% dry matter in the ration. Added liquid feed can assist in reduced sorting.
• Intakes, intakes, intakes. The best formulated ration is of no use if the cows do not eat it. As dry matter intake naturally declines just before calving, anionic supplements may further inhibit intakes. Therefore, consider using molasses liquid feed formulated with anionic supplements to reach both intake and DCAD goals. Liquid molasses is highly palatable and known to encourage feed intake.

(References available upon request)