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Two weeks after calving, cows lose body condition. But if she is short on nutrients, too, that drop-off can set off a chain reaction that's hard to stop.
Don Hubbell has both a producer's eye and a researcher's curiosity when it comes to cattle. He is director of the University of Arkansas Livestock and Forestry Research Station, in Batesville, and has his own cow herd, as well. His aim this time of year is to be sure cows calve at a BCS (Body Condition Score) of between 6 and 7. The same holds for heifers.
While producers tend to think of stressed calves at weaning as most in need of a healthy immune response, their dams have an important role to play. A cow that has her nutritional needs met passes that on in the form of good colostral immunity.
Hubbell's priority on BCS for his cow herd is a smart way of keeping track of what's going on with the immune system, said John Arthington, animal scientist and director of the Range Cattle Research and Education Center, in Ona, Fla.
"The BCS of cows very likely does impact the immune system," he said. But he adds it gets a bit complicated when you look at how cows, like all animals, will partition nutrients. It's kind of like sorting steers. Blacks go in one pen, reds in another, smokes in yet another. But unlike steers, you can't choose where nutrients go. There is, however, a natural order of things.
First is survival. Nutrients always go to survival, or maintenance of organs and systems. Next, the body will use them to maintain pregnancy. Last on the list comes rebreeding, boosting the immune system or, in the case of a heifer, growth.
If there aren't enough nutrients to meet all of those needs, it can be a bit of a gamble.
"Thin cows in poor BCS might, for example, respond to a vaccine. But then they may not become pregnant," Arthington said.
And abundance doesn't mean the herd's nutritional needs are being met. It's as much about what she's eating as how much.
There are essentially three classes of nutrients, and each impacts a cow's immune system in its own way.
ENERGY HOLDS UP BCS
This goes back to body condition, Arthington said. "BCS is a subjective estimate of fat composition," he said. "Fat is energy and a critical nutrient in all physiological processes.
If energy in the diet is limited, the body utilizes stores of energy from the body tissues, fat and muscle."
But, he added, a cow has to be quite thin before she uses up all her fat and has to draw on muscle.
A dry pregnant cow is usually the least needy animal in a herd, but don't make her give up that fat cover. If she weighs around 1,200 pounds, she'll still need 10 1/2 pounds of energy on a dry matter basis.
PROTEINS BUILD ANTIBODIES
Protein can be easy to forget, especially with a dry cow who only requires about 1 1/2 pounds a day. But protein plays a major role in the animal's immune function.
"When a cow is vaccinated, she is asking her immune system to recognize an antigen, or foreign substance, and produce antibodies," Arthington explained. "Antibodies are made of protein-based amino acids and energy."
TRACE MINERALS FIGHT ILLNESS
The tiny superstars of a cow's immune function are trace minerals, especially copper, zinc and selenium. They are part of a chain reaction that helps fight infections and make use of vaccines.