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Monday, March 3, 2014

Calf immunity comes with a ticking clock

by Kerry Halladay, Associate Editor

— Colostrum in the first hours of life is essential

As brand new calves are about to be popping up on the range, the unique nature of their immune system in their first hours and what it means to everyone involved—the calf, the herd, you and your bottom line—are important things to know.

When it comes to calves and their immune systems, most ranchers know there’s a ticking clock counting down the prospects of that calf’s future. They have to get a lot of good colostrum in them as fast as possible or else they are left poorly defended. That causes problems down the line in the form of sickly, poorly-performing or even dead calves. But what’s the why behind that clock and what’s so important about colostrum? Here’s a rundown of the science and the mechanics behind those questions.

Basics of immunity

Very simply, the immune system is a body’s defense mechanism against invaders, be they bacteria, viruses or other pathogens. The immune system has a variety of defenses, including “physical” defenses like the skin, mucus membranes, and bodily fluids like saliva, as well as more internal defenses like white blood cells, T-cells and B-cells and other specialized cells.

There are two main types of immunity: passive and active. Passive immunity is something given or provided to the body which works instantly, while active immunity is created by the body through exposure to pathogens and adaptive reactions and takes some time to form and respond.

In the words of Dr. Reinaldo Cooke, Assistant Professor and Beef Cattle Specialist at Oregon State University, “Active immunity is acquired when the animal is infected by a specific pathogen, creates a ‘memory’ against it, and successfully eliminates the disease and pathogen.”

Vaccines and natural exposure are examples of active immunity in action. In vaccines, a dead or otherwise weakened form of a pathogen is introduced into the animal’s system where its immune system can gain that “memory” against that pathogen in the form of antibodies. Vaccines provide the animal’s system with a way to generate antibodies in a relatively lowrisk situation. The downside with active immunity is that it takes time for the animal’s system to react and create antibodies to effectively address each pathogen.

On the other hand, passive immunity is “when the animal receives antibodies from an external source, such as another animal,” described Cooke. Calves, as with any mammalian infant, are born with fully formed, but immature immune systems. Though it takes until a calf reaches sexual maturity for their immune systems to fully mature, consuming colostrum is the most important element to their immune development from the rancher point of view. This is an example of passive immunity, in that antibodies are passed from the dam to the calf through colostrum.

Colostrum and timing

Colostrum, or “first milk,” is different from a cow’s usual milk in that it contains many things to help jumpstart the calf’s immune system. According to Dr. Victor Cortese, DMV and Director Cattle- Equine Immunology and Biologics at Zoetis, “Constituents of colostrum include concentrated levels of antibodies and many of the immune cells (B cells, CD cells, macrophages, and neutrophils), which are fully functional after absorption by the calf.”

Other elements of colostrum include important nutrients and interferons; proteins that help cells defend against infection, as well as facilitating immune responses. Metaphorically speaking, the contents of colostrum act as both borrowed soldiers from the dam’s immune army, as well as a rallying call to the calf’s own immune army to be on alert for certain foreign interlopers.

As it can take a few days to several weeks for a body’s immune system to create its own antibodies—but then only against those pathogens it experiences and survives—the borrowed protection of the dam’s antibodies transferred through the colostrum is essential to a calf’s survival.

“This transfer is extremely important to newborn calves because their immune system is not mature enough to develop its own antibodies,” noted Cooke. “The calf should be immune to most of the pathogens present in the environment because the dam has already been exposed to them and developed protective antibodies.”

The “borrowed soldiers” time in the calf varies depending on their type and are intended to tide the calf over until it can shore up its own immune system’s numbers. According to various scientific sources, the borrowed immune system benefits calves gain from colostrum dissipates between three to five weeks of age.

The ticking clock of colostrum and calf immunity is rooted in what is called “intestinal closure.”

“When calves are born, the epithelial cells that line the digestive tract allow absorption of colostral proteins by means of pinocytosis [the process by which cells “drink” exterior liquids]. As soon as the digestive tract is stimulated by ingestion of any material, this population of cells begins to change to those that no longer permit absorption,” explained Cortese in his article on neonatal calf immunology.

The process of intestinal closure isn’t an open-andshut situation, but more like a slowly lowering door, a la Indiana Jones. Once the intestinal track is stimulated and those lining cells capable of absorption begin sloughing off, the ability of the calf to absorb the beneficial qualities of colostrum declines.

According to Cortese, about 50 percent of absorption capabilities were gone six hours after a calf was born. By eight hours, that dropped to 33 percent. Glenn Selk, Extension Animal Reproduction Specialist at Oklahoma State University, noted there is a significant drop-off in immunoglobulin absorption after 12 hours, with some calves failing to absorb immunoglobulin at all at that point. It is known that the ability to absorb colostrum is gone by 20-24 hours after birth, even if the calf has been starved of colostrum or a colostrum replacement.

The phenomenon of intestinal closure makes when a calf gets colostrum—not to mention how much and of what quality—have a huge impact on that calf’s wellbeing and eventual immunological success.

“Ideally, we like to see vigorous calves stand and nurse within two hours of birth and repeatedly nurse by the time it is 12 hours old,” summarized Dr. Richard Randle, Extension Beef Veterinarian at the University of Nebraska-Lincoln.

Difficulties

There are a number of difficulties that can arise and get in the way of a calf getting colostrum— enough, the right quality, or in time—of which ranchers should be aware.

Difficult calving: Both calves and dams are worn out by the experience of a difficult birth. Calves are often weak and may be slower to stand and seek out the udder. Cows, for their part, might also be on the ground and reticent to rise, and a calf cannot suckle a recumbent dam. Research has shown that calves born with no assistance got up and nursed more effectively, and had a higher immunoglobulin concentration at 24 hours, than did calves that needed assistance or had a hard birth, according to Randle.

Adverse weather and geography: Anything that makes it harder for the calf to get up or discourages them from standing can negatively impact their access to colostrum. Excessively cold weather will keep the calf on the ground longer and cold stress can negatively affect a cow’s colostrum production. Wet or muddy conditions—or anything that could make those first wobbly steps all the more difficult—can also be a detriment to the calf getting up quickly.

Problem cows: Cows lacking a strong mothering instinct may not lick off their calves properly and the licking off behavior has been shown to be essential in the cow/calf bond. Cows that do not lick off their calf, or do not complete it properly, may not allow the calf to suckle. Cows with poor conformation in the udders and teats can make it difficult for the calf to find the teat. A cow’s nutritional condition also plays a big role; an undernourished cow may not produce the volume and/or quality of colostrum needed.

First-calf heifers: These could also be filed under “problem cows” since heifers are more likely to have birthing difficulties, produce lower volumes of colostrum, and are unskilled as mothers so they may lack a necessary mothering instinct.

Breed differences: Not all breeds are created equal when it comes to quantity and quality of colostrum. Numerous studies show that amount of colostrum produced, as well as the concentration of immunoglobulins in the colostrum, can vary wildly between breeds. Many studies note that more research is required and there are a lot of unknowns regarding how management impacts colostrum production in terms of quantity and quality.

Colostrum replacements and supplements exist to assist calves in need, but care must be taken with what product is selected. The difference between replacer and supplement depends on the concentration of immunoglobulins—higher and theoretically sufficient to sustain the calf independently for replacement and lower for supplement—but differences exist within the different product,s as well.

“There are other nutrients such as sugars, fats, vitamins and minerals in replacements, but there can be variability in the quality and digestibility of products based on the source of these nutrients and the method of processing” said Randle, who cautioned producers to carefully read and follow manufacturer’s instructions regarding product mixtures and recommended feedings, as they can vary.

“You should consult your veterinarian to help you make a more informed purchasing decision for the colostrum replacement product that is suited best for your operation. This decision is an important one because you only get one chance to start a calf off right.” — Kerry Halladay, WLJ Editor

What is an antibody?

Antibodies—also known as immunoglobulins—are proteins produced by specialized cells that help the immune system recognize, and thereby attack, threats it has encountered before. Large cells called macrophages “eat” or otherwise engulf and destroy debris and pathogens in the body. In doing so, they release short protein chains, called antigens, on their surface that identify whatever threat it “consumed.” These antigens can break off the surface of the macrophage and adhere to the surface of B cells. When T cells “see” the same antigen on the surfaces of macrophage and B cells, it triggers the productions of antibodies in B cells. Antibodies produced by the B cells then adhere to other examples of the pathogen, which spawned its creation, and make it easier for macrophages to identify and consume those other examples of the pathogen.

 
 


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