|One-fourth of first-calf heifers might be subclinically hypocalcemic,
leading to post-calving difficulties.
While few first- and second-calf heifers succumb to milk fever, 25% of first-calf heifers may be subclinically hypo-calcemic and more than half of later lactation cows will be.
"At calving, cows can mobilize up to nine times as much calcium as normal for colostrum production,” says Bob Corbett, a veterinarian with Dairy Health Consultation in Spring City, Utah.
That calcium drain from the bloodstream can lead to a whole host of problems following calving. Muscle contraction can be impaired, resulting in more retained placentas, slower uterine involution and displaced abomasums.
"The slowing down of the gastrointestinal tract often results in decreased dry-matter intake [DMI],” Corbett says. "Animals in severe negative energy balance also do not have the [energy and protein] to respond to invading pathogens as effectively, and often experience problems with infectious disease early in lactation.”
Calcium also plays an integral role in immune function and is involved in the intracellular signaling of white blood cells. "White blood cells of animals with hypocalcemia have a reduced ability to respond to invading pathogens,” Corbett says. And cows with hypocalcemia are much more likely to develop ketosis due to lower DMI.
Calcium levels drop prior to calving for three reasons:
To ensure cows
- Feed DMIs typically plunge as dry cows are shuffled from group to group.
- The calf's skeleton grows rapidly in the three weeks prior to birth, pulling calcium from the dam's bloodstream to build bone.
- The cow begins mobilizing her calcium as she gears up to produce colostrum for the newborn calf. This process typically starts up to five weeks prior to calving.
are maintaining DMI through the dry period, Corbett says it is imperative that they spend three weeks in the close-up pen.
Corbett summarized data from five of his clients' herds with a total of 13,000 cows. He found that each additional week in the close-up pen equaled another 1,000 lb. of milk production per lactation.
It's also critical that close-up pens and postfresh pens have plenty of bunk space. Corbett recommends a stocking rate of 80% of lockups in both the close-up pen and post-fresh groups. Where possible, maintain separate pens for springing heifers and older cows for both close-up and postfresh groups.
Also, minimize the number of pen moves. "In today's larger dairies, it has become commonplace for the transition cow to be moved five more times during this period,” Corbett says. "Each of these moves requires a social adjustment where the animals have to reestablish dominance.
"This almost always results in a decrease in dry matter intake in an animal that is already decreasing intake as she approaches calving,” he says.
During this critical period, Corbett says, producers will need to pay particular attention to:
- Ration formulation.
- Feed palatability.
- Bunk management.
- Cow comfort.
- Calm handling.
- Close observation and prompt treatment of milk fever, ketosis and mastitis should they occur.
More detail on calcium function from 2009 NMC Proceedings
Reduce Pen Moves