When is hypocalcemia the most prevalent?
The start of lactation challenges Ca homeostasis (balance) in the dairy cow. There is a sudden loss of Ca from the blood into the colostrum at the time of calving. It takes 3 to 4 days for Ca to start being mobilized from the bone into the blood stream. During that time period cows are at increased risk for subclinical hypocalcemia.
What are the key risk factors for hypocalcemia?
1) Increasing parity (lactation number) increases the risk for hypocalcemia because the loss of Ca resorption capacity from the bone is linked to declining skeletal growth. First lactation cows are at low risk for subclinical hypocalcemia because they are still growing and the bone still has good resorption capability, therefore, they are able to mobilize Ca easier than older cows.
2) Increasing milk yield increases the risk for hypocalcemia because colostrum production increases thus increasing the amount of Ca removed from the blood stream at parturition.
Why is there a concern about low blood Ca if a cow is not showing clinical signs of hypocalcemia?
Calcium is the highest priority mineral. It is essential for muscle and nerve function. It is involved in skeletal muscle strength, GI motility (smooth muscle function), and is also important in immune function. Subclinical hypocalcemia increases the risk for certain metabolic diseases (increased risk for metritis, ketosis, displaced abomasum (DA), and decreases immune function) thus increasing the risk that an individual cow may be removed from the herd.
How can subclinical hypocalcemia be prevented or minimized?
There are 2 primary methods of prevention for subclinical hypocalcemia (diet and oral supplementation of Ca). Nutritional strategies that have been found to be effective in reducing the incidences of hypocalcemia included;
1) low Ca diets prepartum,
2) dietary acidification prepartum
3) increased Mg in the prepartum diet
These nutritional strategies have been shown to be beneficial in reducing the incidences of hypocalcemia, but subclinical hypocalcemia cannot be prevented through diet alone (Oetzel). Oral Ca supplementation has been found to be effective in reducing the incidences of subclinical hypocalcemia especially when used in combination with nutritional strategies. Cows absorb oral Ca rapidly and sustain increased blood level Ca for 4 to 6 hours. There are different types of oral Ca supplementation. At this meeting, Dr. Oetzel spent most of his time discussing Bovikalc® which is a fat-coated bolus that contains a combination of calcium chloride and calcium sulfate. Calcium chloride and calcium sulfate invoke an acidogenic response in cows which will cause the cow to mobilize more Ca from her skeleton. Oetzel recommends giving two doses, about 12 hours apart. Give the oral Ca bolus at calving (if the cow is not ‘down’) and another bolus 12 hours later to give a sustained improvement in blood Ca levels.
What are some successful oral Ca strategies for cows?
Oetzel states not to give oral Ca to down cows. Oral Ca supplements do work for early milk fever cases (before the cow goes down), after successful treatment of down cows, for off-feed cows (especially early lactation), and to cows with impaired intestinal motility (subacute ruminal acidosis).
When do you use IV instead of oral calcium?
If a cow is ‘down (recumbent)’ because of clinical hypocalcemia (milk fever; <4 mg/dL of Ca in blood), Oetzel recommends giving a bottle of Ca borogluconate via IV infusion. Down cows can quickly suffer irreversible musculo-skeletal damage. The IV delivers 10.5 grams of Ca directly into the blood which causes a massive spike in blood Ca, and will help many cows recover quickly from milk fever. However, there can be some side effects from elevating blood Ca so high. Occasionally, a cow will die from cardiac arrest when a bottle of Ca is given because when blood Ca concentrations are at or above 20 mg/dL there is an increased risk of cardiac arrest (because of this threshold, it is never recommended to give a second bottle of Ca with the initial IV treatment). Secondly, some of the cows that were given a bottle of Ca for clinical hypocalcemia will relapse with another case of clinical milk fever and need another bottle of Ca. Oetzel suspects this is due to what he terms the ‘Calcitonin Response’, where the spike in blood Ca from the IV signals the hormone calcitonin to release. Calcitonin does not allow Ca to mobilize from the bone, therefore the blood Ca levels end up dropping lower than the normal cows.
Oetzel’s Comments/Conclusions:
- Don’t give oral calcium to a down cow.
- Don’t give IV calcium to a standing cow.
- Clinical hypocalcemia (down cows; blood Ca <4 mg/dL): Use both IV and oral forms of Ca treatment.
- Initially, give IV of Ca
- Followed by 2 oral Ca boluses.
- Give the 1st Ca bolus 12 hours after IV injection and the 2nd Ca bolus 12 hours later.
- Give oral Ca to 2nd and greater lactation cows (Don’t give to 1st lactation cows)
- Subclinical hypocalcemia (≤8.6 mg/dL in blood the day of calving): Use both nutritional intervention and oral Ca supplements.
- The nutritional intervention usually happens during the prepartum period.
- Give 1 oral Ca bolus at calving followed by another oral Ca bolus 12 hours later.
- If the dairy only wants to give 1 bolus (which Dr. Oetzel wasn’t recommending) give it the day after calving
- If you give oral Ca around calving give CaCl2 (do not give drench buckets such as calcium propionate because the glucose suppresses appetite by signaling the cow is full).
- 36 hours after calving it is okay to give the drench bucket (Ca with glucose).
Written by: Lynn VanWieringen
