Getting cows off to a good start at the beginning of lactation can sometimes be a struggle. Hypocalcemia—also known as milk fever—is often the culprit, triggered by a drop in blood calcium levels.
“Historically, when we think of hypocalcemia, it’s those cows that go down and are unable to stand around the time of calving,” said Jen Roberts, DVM, Boehringer Ingelheim. “They may also have difficulty calving because they don’t have enough blood calcium for uterine contractions to deliver the calf. Those are the cows we see.”
However, those obvious cases are only part of the story. It’s often the cows that aren’t showing visible signs that experience broader challenges.
“Subclinical hypocalcemia, by definition, is something you don’t typically see, especially in healthy cows, which are the most susceptible,” explained Curt Vlietstra, DVM, Boehringer Ingelheim. “If you want to address it, you need to be aware that it is a problem.”
Even without visible symptoms, subclinical hypocalcemia can influence performance in several ways:
• Lower feed intake
• Reduction in milk production
• Lack of muscle contractions can cause a retained placenta, leading to uterine infections
Because subclinical hypocalcemia is difficult to identify, focusing on prevention is a must.
“To set cows up for success, we need to manage them well during the pre-fresh period to make sure we’re preventing low blood calcium, and then supporting calcium levels through calving and the transition period with a well-formulated bolus,” Roberts said.
Prevention starts in the pre-fresh pen, where nutrition plays a central role in preparing cows for calving. Typically, third-lactation and older cows are the most susceptible to hypocalcemia. Second-lactation cows may also struggle with low blood calcium.
“Some farms will use what is called a negative dietary cation-anion difference [DCAD] in the diet during the pre-fresh period to get the mature cows prepared for calving,” said Roberts.
DCAD is a balance of cations (potassium and sodium) and anions (chloride and sulfur) in the diet. Generally, in the last three weeks of pregnancy, a negative-DCAD diet will be fed to cows.
“It is a way to acidify the diet in the pre-fresh period to help prevent subclinical or clinical hypocalcemia,” noted Roberts.
Cows are at their lowest blood calcium levels 18 to 24 hours after calving. Because of this dip, supplementing cows with a calcium bolus can help support their calcium needs during the transition period.
“After calving, supplementing cows with an oral, rapidly dissolving, readily available calcium bolus will help support their needs,” shared Roberts. “If we’re not supporting those cows and providing additional calcium to keep them going smoothly through that transition, it can negatively impact their lactation and longevity in the herd. We need to ensure we provide supplemental calcium to support cows, so they can get lactation off to the best start.”
Providing additional support with a second bolus within 12 to 24 hours post calving can further set cows up for success.
“Coming back in with a second calcium bolus will help those high-producing cows have enough calcium to make milk and get off to a good start of lactating,” said Vlietstra. “It will also help keep all of their organs and internal systems working so they are healthy, and we can keep them out of the sick pen.”
There are many calcium bolus options available. It is critical to examine their ingredients, as the type of calcium directly affects how quickly and effectively cows can use it.
The types of calcium in those boluses fall into two groups: acidogenic or alkalogenic.
Acidogenic boluses are recommended, because they help increase the responsiveness to the body’s signals to move calcium into the blood from the cow’s bones.
“A bolus that has acidogenic calcium is not only going to provide her with a rapidly absorbable form of calcium, but it is also going to encourage her body to move calcium out of the bones in response to the demands at the beginning of lactation,” said Dr. Roberts.
The other commonly used calcium is the alkalogenic type, calcium carbonate, found in many commercially available boluses.
“Calcium carbonate isn’t as rapidly absorbed by the cow as calcium chloride or calcium sulfate,” related Roberts. “It doesn’t encourage the cow’s body to do its own mobilization of calcium from her internal stores of calcium.”
An ideal bolus is about two-thirds calcium chloride and one-third calcium sulfate for optimal absorption. This combination provides rapid availability and sustained support during the transition period.
“It’s not just the differences in the types of calcium in the boluses, but the quality that matters,” added Vlietstra.
When evaluating boluses, look for a few key quality indicators:
• Use a bolus with a fat coating, because it makes administration easier and safer for both workers and fresh cows.
• Avoid products with fillers or the wrong calcium forms.
Reading ingredient labels on calcium bolus supplements and pairing them with balanced nutrition help ensure your cows reach their full lactation potential.
A successful transition period depends on more than one intervention. By combining balanced pre-fresh nutrition with a high-quality calcium bolus program, you can support metabolic health, reduce fresh-cow interventions, and promote a smoother path into early lactation. These steps help cows perform at their best when it matters most. — Boehringer Ingelheim
