Source: University of Minnesota
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.
Nutritional and management strategies can decrease the losses it causes and optimize post calving health, milk production and reproductive performance.
Milk fever, or hypocalcemia, has been a problem of fresh cows for over two centuries. Effective nutritional management during the dry period and early lactation has decreased clinical cases of milk fever to rates lower than 1 percent. On the other hand, subclinical cases have been reported to affect as many as 73 percent of animals of third and greater lactation.
Risks and costs of milk fever
Traditionally, milk fever has been associated with higher risk of dystocia, uterine prolapse, retained placenta, mastitis and displaced abomasum.
Decreased milk production, decreased immune function, increased risk of ketosis, decreased reproductive performance, and increased risk of early removal from the herd are the negative consequences of subclinical hypocalcemia.
Taken together, the cost of the direct and indirect effects of hypocalcemia on animal health and production can be substantial in a 250-cow herd. So, prevention of hypocalcemia is extremely important not only for animal health but also for the profitability of dairy farms.
The difference between milk fever and subclinical hypocalcemia
Both types of hypocalcemia are characterized by low blood calcium concentrations (less than 8.0 milligrams per deciliter).
Milk fever cases are characterized by the development of clinical signs:
In subclinical hypocalcemia cases there are no clinical signs, making it much harder to detect.
It is extremely important to understand this difference when developing standard operating procedures in dairy farms, since administering intravenous calcium is only recommended for clinical cases.
Milk fever cases should be treated with 500 milliliters of 23 percent calcium gluconate IV and followed by the administration of two oral calcium bolus given 12 hours apart. It is important to emphasize that oral calcium bolus should not be administered if cows do not respond to the calcium IV treatment.
In milk fever cows, failing to rise after treatment with IV calcium is a signal that normal muscular function has not been reestablished. Cows may choke on the calcium bolus if treatment is given while they are still down. A veterinarian should be consulted and further treatment should be evaluated when milk fever cows do not respond to IV administration of calcium.
Do NOT give calcium IV to cows with no signs of milk fever
Contrary to the milk fever cases, supplementation with IV calcium to dairy cows with subclinical hypocalcemia is not recommended.
Giving a calcium IV to dairy cows with subclinical hypocalcemia can result in a long term decrease in blood calcium concentration. Researchers found that blood calcium concentration reached levels even lower than their baseline six hours after treatment. Moreover, blood calcium concentration remained lower than the levels measured in cows that did not receive any IV calcium.
Minimize the risk
Since dairy cows with subclinical hypocalcemia do not show clinical signs, and cow-side measurements of blood calcium concentrations are very expensive, subclinical hypocalcemia is rarely diagnosed in commercial farms. Despite that, giving two oral calcium bolus (first bolus immediately after calving and second bolus 12 hours later) to lame and high producing cows (two or more lactations) can minimize the risk of developing milk fever.
Giving calcium bolus to this group of cows (approximately 51 percent of the animals in an average dairy in the United States) can result in a return on investment of 180 percent ($1.80 of return for each $1.00 invested).
How to decide treatment of dairy cows with hypocalcemia during early lactation
Is the cow standing?
- Give 500 mL of 23% calcium gluconate IV
- Follow with 2 oral calcium bolus
- 1st bolus when cow stands up again
- 2nd bolus 12 hours later
- DO NOT give calcium IV
- Give 2 oral calcium bolus
- 1st bolus immediately after calving
- 2nd bolus 12 hours later
Lowering blood pH can prevent hypocalcemia
There is a variety of different nutritional strategies to prevent hypocalcemia. Feeding low potassium diets or forages during the pre-fresh period can result in a change in the dietary cation-anion difference (DCAD), which will, in turn, cause an acid-forming response in dairy cows. This response is essential to improve the cow’s ability to mobilize calcium from the bones and to absorb dietary calcium from the small intestines.
However, the changes resulting from the use of low potassium diets and forages may not be enough to lower blood pH. So the use of anionic salts is recommended to further decrease the blood pH in order to improve calcium metabolism.
These adaptations are essential to support the cow’s elevated calcium demands for colostrum and milk production around calving. The use of low potassium diets in association with mineral anionic supplement during the pre-fresh period has effectively contributed to the decrease in hypocalcemia in dairy farms across the United States.
When feeding anionic salts during the pre-fresh period, it is extremely important to monitor if the mineral supplements are working. The easiest method for monitoring the effectiveness of the DCAD diet is by measuring urine pH in prepartum dairy cows that have been consuming anionic salts for at least two days. Urine pH of cows consuming DCAD diets should be within the 6.0 to 6.5 range.