In the December 2012 issue of the Farm Report I highlighted work indicating that fresh cows experience low blood calcium more than previously thought. In a survey of 480 herds in 21 states, 47% of cows had subclinical hypocalcemia (aka subclinical milk fever) within 48 hours of calving. Subclinical hypocalcemia is a threat to transition cow health and farm profitability. A cow doesn’t need to be “down” to be negatively affected by hypocalcemia. It results in decreased early lactation milk yield, increased risk for ketosis and displaced abomasum, and reduced fertility at first service. Subclinical hypocalcemia is of greater economic importance than clinical cases of milk fever because it affects a higher proportion of cows, according to Dr. Oetzel from the University of Wisconsin. If a 1000-cow dairy has a 2% annual incidence of clinical milk fever and each case costs $300, then the cost to the dairy is $6000 per year from clinical cases. If the same herd has a 30% annual incidence of subclincal hypocalcemia in 2nd and greater lactation cows (2/3 of the herd) and each case costs $125 because of reduced milk yield and treatment cost of ketosis and displaced abomasum, then the cost to the dairy is $24,750 or about 4 times greater than the cost of the clinical cases.
What can you do about subclincal hypocalcemia in your herd? The best option for treatment of cows with hypocalcemia that are still standing is to give them an oral calcium supplement at least twice, one at calving and another the next day, according to Dr. Oetzel. The calcium is absorbed into the bloodstream within about 30 minutes of administration. The blood calcium will remain elevated for about 4 to 6 hours. Intravenous (IV) calcium is not recommended for treating cows that are still standing. In standing cows, treatment with IV calcium causes extremely high blood calcium levels that increase the risk for fatal heart complications. Treatment with subcutaneous (SC) calcium is an option since the calcium is well-absorbed in hydrated cows, but it has some limitations. It may be ineffective in cows that are dehydrated or severely hypocalcemic. Calcium solutions given SC can be irritating and cause tissue necrosis. Avoid giving SC calcium solutions containing glucose since glucose is poorly absorbed and can lead to abscesses and tissue sloughing.
Prevention is my preferred approach to “treating” subclinical hypocalcemia. Use of a low or negative dietary cation-anion difference (DCAD) in the close-up diet is an effective way to increase blood calcium during the period immediately after calving. According to Drs. Beede (Michigan State University) and Block (Church & Dwight Co.) targeting DCAD at -10 to -15 mEq/100 g is typically effective for changing acid-base status and increasing blood calcium. This target level includes a safety factor to account for changes in mineral content of feeds and variation in response from individual cows. To achieve this target range, reduce K+ and Na+ as much as possible while still meeting minimum requirements and then add anions from either anionic salts or commercial products. It’s important to monitor urine pH when using a DCAD approach in the close-up period. Most cows should have a pH between 6.2 and 6.8. If the pH is <5.5 then the DCAD is too low and needs to be adjusted.
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