Preventing and treating milk fever and subclinical hypocalcemia
Even though it is practically impossible to eliminate hypocalcemia from a dairy herd, the adoption of strategies that prevent this health disorder is key to any successful transition cow program. The adoption of nutritional and management strategies to prevent hypocalcemia are important to decrease the losses caused by it and to optimize post calving health, milk production, and reproductive performance.
Effective nutritional management during the dry period and early lactation can decrease the occurrence of milk fever to rates lower than 1%. However, subclinical hypocalcemia (cases without recognizable signs and symptoms) may affect as many as 73% of animals of third and greater lactation.
Taken together, the cost of the direct and indirect effects of hypocalcemia on animal health and production can be up to $9,162 per year in a 250-cow herd.
The difference between milk fever and subclinical hypocalcemia
Low blood calcium concentrations, less than 8.6 milligrams per deciliter, are common in both types of hypocalcemia.
The development of clinical signs (i.e. down cow, lethargy, cold extremities, and rumen atony) define milk fever cases. Traditionally, milk fever has been associated with higher risk of abnormal birth, uterine prolapse, retained placenta, mastitis, and displaced abomasum.
Subclinical hypocalcemia cases do not show clinical signs. The consequences of subclinical hypocalcemia include decreased milk production, decreased immune function, increased risk of ketosis, decreased reproductive performance, and increased risk of early removal from the herd.
This difference is important when developing standard operating procedures in dairy farms since you should only use intravenous (IV) calcium for clinical cases.
- Milk fever cases should be treated with 500 mL of 23% calcium gluconate IV followed by the administration of two oral calcium boluses given 12 hours apart.
- Do not administer the oral calcium bolus if cows do not respond to the calcium IV treatment.
- Failing to get up after treatment with IV calcium is a signal that there has been a failure in establishing normal muscular function.
- Cows may choke on the calcium bolus if treated while they are still down.
Consult a veterinarian to evaluate further treatment options when milk fever cows do not respond to IV administration of calcium.
Contrary to milk fever treatment, do not give IV calcium to dairy cows with subclinical hypocalcemia as this can result in a longterm decrease in blood calcium concentration.
Commercial farms rarely have diagnosed cases of subclinical hypocalcemia. To minimize the risk of milk fever development, administer two oral calcium boluses (first bolus immediately after calving and second bolus 12 hours later) to lame and high-producing cows.
The administration of calcium boluses to these groups of cows, which account for approximately 51% of the animals in an average dairy in the United States, can result in a return on investment of 180%, or $1.80 of return for each $1.00 invested.
Figure 1. Decision tree for the treatment of dairy cows with hypocalcemia during early lactation.
The use of low potassium diets or forages along with mineral anionic salts during the pre-fresh period has effectively contributed to the decrease in the incidence of hypocalcemia in dairy farms across the United States.
Feeding a low potassium diet during the pre-fresh period will improve the cow’s ability to mobilize calcium from bones and to absorb dietary calcium from the small intestines. Adding anionic salts decreases blood pH and improves calcium metabolism in order to support the cow’s elevated calcium demands for colostrum and milk production around calving.
When feeding anionic salts during the pre-fresh period, you must monitor whether the mineral supplements are achieving the expected blood acidification. The easiest method for monitoring the effectiveness of this diet is by measuring urine pH in pre-partum dairy cows that have been consuming anionic salts for at least 2 days. The urine pH of these cows should be within the 6.0 to 6.5 range.