A closer look at hypocalcemia

Not all milk fever is the same

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JUNEAU, Wis. — Fresh cows are at a vulnerable stage in their lactation, with a lot of potential for health problems. 

Dr. Luciano Caixeta, Ph.D., associate professor of dairy production medicine, University of Minnesota, is studying the age-old condition in fresh cows that most farmers unfortunately have dealt with more than they would like to — hypocalcemia, or milk fever. 

Caixeta spoke on a Nov. 1 The Dairy Signal through Professional Dairy Producers.

Having grown up as the son of a veterinarian and later practicing veterinary medicine himself, Caixeta felt it was important to take a closer look at hypocalcemia and studied the condition during his Ph.D. training.

“As a veterinarian practitioner, I was tired of getting called in the middle of the night over something that definitely could be prevented,” Caixeta said. “We have come a long way since beginning clinical practice.”

Caixeta said it is important to remember that all cows experience some level of hypocalcemia during the calving process and beginning days of postpartum. 

Hypocalcemia by definition simply means low blood calcium concentrations. Early-lactation cows have an elevated calcium demand that is not matched by the capacity they have to absorb calcium through their gut or to mobilize calcium in their bones to reabsorb it. Because they cannot meet this demand of calcium, they go into a hypocalcemic state. 

“If the cow has clinical signs, so she’s down and cannot get up — all those classic signs of milk fever — that’s what I call clinical hypocalcemia or milk fever,” Caixeta said. “All the other (signs) — the cow that’s a little bit unstable, maybe has cold ears, you can tell that she’s not fully all right, there is something going on — if it’s not any of the other diseases, it’s likely low blood calcium. Then that’s what I consider subclinical.”

Caixeta said there are physiological differences between those cows and a physiological reason for those treatments to be different. 

Subclinical hypocalcemia is seen more in cows that are in their third or greater lactation. This is because they have a greater concentration of calcium to make up due to the larger volume of colostrum and milk production. On average, the older cows are still experiencing a lower calcium concentration on the second day after calving. 

Caixeta said this information was not readily available until 2017. 

“We have reports of milk fever for 200 years, so something that is seven years old is new,” Caixeta said. “Cows that drop and stay low for longer are what I have coined the term (as being) persistent hypocalcemic, where they drop and don’t come up.”

He said that persistent hypocalcemic cows are 4.1 times more likely to develop further diseases and eventually exit the herd. 

The treatment for clinical cases where the cow is down is still a bottle of calcium administered intravenously. For a subclinical case where the cow is still standing, a calcium bolus administered orally remains the answer. Caixeta does not recommend two bottles given in an IV at the same time because the calcium levels will reach a fatal concentration. Also, an oral bolus should not be given to a down cow since the lack of calcium will not allow her muscles to flex normally and the possibility of choking is greater. 

Caixeta has focused on nutritional strategies as a preventative measure in reducing the amount of hypocalcemic cases on farms. 

One effective way to prevent milk fever nutritionally is with the use of anionic salts. By including these in the diet, the cow is getting acidified in the prepartum period, leading her to mobilize more calcium already. 

Then, as she mobilizes more calcium that she does not need, it gets excreted. The difference is shown in the pH of urine; the calcium is being mobilized. By the time the cow produces colostrum or milk, she is already primed to mobilize the calcium she needs. That is when, instead of excreting calcium into the urine, the cow mobilizes it into the milk and avoids having such low calcium and becoming clinically ill.

Another nutritional strategy is the use of Zeolite, which is a mineral binder. This is like a rock material that will bind to minerals. Using it will decrease the amount of minerals in circulation, the main ones being calcium and phosphorus. This enables the cow to mobilize more calcium effectively. 

“When I started practice 15 years ago, we used to see way more clinical cases,” Caixeta said. “We think with the improved nutrition, we have decreased the number of hypocalcemic cows so that it is common to have less than 1% of clinical cases on a farm.”

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