By Phil Durst, Michigan State University Extension
Should we consider routine treatment of subclinical milk fever? How does that differ from treating clinical milk fever?
If a large percentage of your cows are likely hypocalcemic should you be treating cows routinely? In an earlier Michigan State University Extension article, "Cows can suffer from milk fever even though you don’t see it", we presented the evidence that possibly half of your second lactation and older cows are hypocalcemic in the first 24 hours after calving and the costs of that disorder to the herd are great. Based on that, how should you treat cows for this?
At the 2103 Tri-State Dairy Nutrition Conference, Garrett Oetzel, University of Wisconsin Department of Medical Sciences, reported the results from several investigations on the impact of various treatments for hypocalcemia including administering calcium intravenously, subcutaneously or orally. The results can help you develop more effective treatment protocols for your herd.
In developing a treatment protocol, one decision point is whether the cow is still standing (subclinical hypocalcemia and Stage I milk fever) or if the cow is down (Stage II or III). Oetzel does not recommend IV or subcutaneous calcium for a cow that is standing. For these cows in the earlier stage of milk fever, he only recommends oral calcium.
When 500 milliliters of 23 percent calcium gluconate is given via IV infusion, it provides a rapid increase in blood calcium. In an emergency situation, that increase is good and needed. Therefore, Oetzel recommends that any cow that is down with milk fever should immediately be given 500 milliliters slowly. There is a risk with IV treatment, however, because blood calcium may increase too much and cause a heart attack. Additionally, after the initial rapid blood calcium increase, there is a rapid decrease that puts the cow back into hypocalcemic state again approximately 4 hours later.
Giving larger doses of IV calcium provides no additional benefit to cows with milk fever and does not prevent the rapid post-dosing calcium decrease. Rather, the recommendation to reduce the risk of relapse is to give oral calcium to cows that respond to the IV treatment and are able to swallow, followed by a second oral dose 12 hours later.
Subcutaneous calcium administration has a number of problems. In order for the calcium to be absorbed there must be adequate circulation of blood to the peripheral tissues. Peripheral circulation may be compromised in cows that are severely hypocalcemic or dehydrated. Additionally, injected calcium is caustic and can cause tissue necrosis at the injection site. Thus, the full dose needs to split over 6 to 10 injection sites that are widely spaced. Calcium solutions containing glucose should not be given subcutaneously because the glucose is absorbed very poorly this way and can cause abscessing and tissue sloughing.
Oral administration of calcium has the advantage of being absorbed from the digestive tract like calcium in feed ingredients. However, producers and employees often do not like giving oral calcium. Calcium gels may cause ulceration of the mouth and digestive tract, induce metabolic acidosis and reduce feed intake. When giving a liquid solution of calcium, you run the risk of pulmonary aspiration and dissolved chloride is severely caustic to the upper respiratory tissues. Calcium propionate is less caustic but has a slower absorption rate and must be given as a higher proportion of calcium compared with calcium chloride to insure sufficient calcium absorption.
Oetzel tested a commercially available calcium bolus with 43 grams of calcium as calcium chloride and calcium sulfate. The bolus is fat coated and made with gums and was neither caustic nor unpalatable. It apparently disintegrated rapidly once administered and provided both a rapid calcium release as well as a sustained calcium release. The label says to give one bolus at calving and another 12 hours later.
In a trial with herds at low risk for milk fever, and therefore unlikely to respond to calcium supplementation, they administered the calcium bolus once at calving and again the next day to randomly selected cows. They identified those cows that had the best response to oral calcium. Those cows that responded best included about half of all second and later lactation cows, cows with higher than average milk production in the previous lactation and lame cows. Furthermore, these cows gave 6.8 pounds more milk at the first DHI test date than non-supplemented cows.
A difficulty in effectively providing oral calcium treatments is that we cannot accurately predict which cows are most likely to respond to treatment. Therefore, we have to consider protocols for many fresh cows in a herd by defined parameters such as older cows or cows with previous milk fever problems. In herds that do not feed anionic supplements, and/or where transition cow problems are being detected, supplementing all fresh cows with calcium boluses may be economical.
The tested oral calcium boluses cost $6-7 each when purchased in bulk, making the cost of one full treatment regimen $12-14. At the higher end of that spectrum, it would take 70 pounds of milk (@ $0.20/pound) over the lactation to pay for the treatment if milk yield alone was the only benefit. If supplementation also decreased incidence of displaced abomasums (DA), ketosis and metritis, thus resulting in improved reproductive performance, then the value of treatment could be considerably greater.