“My cows aren’t taking off after calving,” said a recent caller to my Michigan State University Extension office. Maybe your dairy farm has experienced the same problem and you are wondering how to your herd get off to a better start after calving. What if there is something holding them back that you don’t see? Maybe there is.
Low blood serum calcium, called hypocalcemia, may be prevalent in your herd, even if you rarely see milk fever cases. It has been reported that in herds fed typical dry cow rations, approximately 50 percent of cows that are second lactation and older will be hypocalcemic in the first 24 hours after calving; even when the rate of clinical milk fever is less than 5 percent. Hypocalcemia may result in lower dry matter intake, lower milk production, higher incidence of metabolic disease and poorer reproductive performance.
Defining the disease
At the 2013 Tri-State Dairy Nutrition Conference, Garrett Oetzel, University of Wisconsin Department of Medical Sciences, defined subclinical hypocalcemia as a blood serum calcium level of less than 8.5 mg./dl. Clinical hypocalcemia, also known as milk fever, is severe hypocalcemia and can be categorized by the severity of the symptoms. Cows with Stage I hypocalcemia have early signs of milk fever without going down. Symptoms include nervousness, weakness, excitability, and frequent shifting of their weight frequently while standing. Stage II is defined as cows that are down but not flat on their side. They typically lie with their head turned into their flank and exhibit moderate to severe depression. Stage III cows are lying flat out and severely depressed. If not treated immediately, death is imminent.
However, many cows that are hypocalcemic may be in the subclinical stage and suffer the effects of hypocalcemia but go undetected. In fact, the economic cost of these subclinical cases to the herd is far greater than the cost of clinical milk fever because the incidence is so much higher and the impacts are seen in secondary health effects. Jesse Goff of Iowa State University calls subclinical or clinical milk fever a gateway disorder. For example, low serum calcium levels lead to reduced smooth muscle contraction. As a consequence, displacement of the abomasum (DA) may occur. Reduced contraction of the sphincter muscle at the teat end may allow bacteria to enter and cause mastitis.
We have been defining subclinical hypocalcemia by the blood serum level of cows from samples taken 12 to 24 hours after calving. While it is possible to take those samples and have them analyzed to monitor the extent of subclinical hypocalcemia, the fact is that we cannot control the problem at this time by monitoring and responding. Therefore, when it comes to subclinical hypocalcemia producers can either emphasize prevention or treatment. In this article we’ll discuss prevention and in a separate article, treatment.