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Factors that hinder calf immunity

Calving Health with Heather Smith Thomas

Illness occurs when an animal’s body is overwhelmed by infection. A healthy animal with strong immunity is less likely to become sick than an animal with poor immunity. Immunity refers to the body’s ability to fight off pathogens, and this ability is developed in a complex process in which the body creates specific weapons for fighting specific invaders.

One type of weapon involves production of antibodies. When pathogens such as viruses or bacteria enter the body, they start invading tissues and causing damage by multiplying and creating toxic products. This damage stimulates the body to create an antibody (a serum protein called an immunoglobulin) to react with the invading agent and neutralize it. These antibodies are carried throughout the body in the bloodstream. The main role of one type of lymphocyte (white blood cell) is to produce antibodies — the proteins that can neutralize certain infectious agents.

If an animal already has antibodies against a specific disease organism, then any time that particular organism invades the body again an army of white blood cells (as well as antibodies) converge on the site to kill the invader. Exposure to one strain of an organism may result in immunity to that specific strain, but might not protect against other strains of the same organism. Antibody immunity depends on the level of exposure, stresses on the animal, general nutrition status and current health. A severe outbreak of disease in a herd may eventually break down a healthy animal’s immunity, and will overwhelm a severely stressed animal’s defenses even sooner.

Vaccination can stimulate production of antibodies, since the vaccine serves as the antigen (like an invading pathogen). The body builds protective antibodies to fight the perceived invader. Then when the animal comes into contact later with the actual infectious agent, the antibody is present in the bloodstream and can inactivate the pathogen. If enough antibodies are present to inactivate the agents that invade the body, the animal will not get sick, and the invasion stimulates rapid production of more antibodies for future protection.

A cow in a natural environment may not become exposed to very many disease-causing organisms, but many cattle are confined some parts of the year (in corrals, small pens or pastures that have been contaminated by heavy cattle use) and come in contact with other cattle — with much more chance of disease spread. But with vaccination and natural exposure to various pathogens, the cow develops many antibodies and strong immunity. During the last part of pregnancy the cow puts these antibodies into the colostrum she produces, so that the calf can have some instant immunity right after it suckles. Thus the first things that might hinder calf immunity are poor-quality colostrum from the dam, an inadequate amount of colostrum, or not getting colostrum in a timely manner.

Passive immunity from colostrum

Dr. Andy Acton of Deep South Animal Clinic in Ogema, Sask., reminds us baby calves are not born with their own antibodies. “They have to absorb antibodies from their mother’s colostrum because they don’t get any from her while they are in the uterus. This passive immunity from colostrum is very important,” he says.

“There are more factors gained from the colostrum than the antibodies absorbed when calves suckle the first time. There is also some absorption of white blood cells of different kinds in that colostrum — from their mother. These, and some of the immune modulators are not present in a colostrum replacer you’d buy.”

Newborns have a limited window of time to absorb antibodies from their mother’s colostrum. “Optimal time is during the first six hours of life, but it can be less in certain conditions, perhaps just the first two hours in cold weather. There are factors that shorten this window, and also some things that lengthen it,” says Acton.

As soon as the calf suckles, the “open gut” starts to close, to prevent absorption of pathogens. Suckling stimulates the gut to close up, because it’s a race between the antibodies from colostrum and pathogens the calf might ingest. If the calf manages to suck a little, or if you feed him a little, the gut closes up quicker than if the calf has had nothing. “The time window for the gut to absorb something in this situation is longer than if the calf gets a small amount of colostrum,” he explains.

What’s the risk for disease and what does the calf need?

Dr. Eugene Janzen, professor, production animal health, faculty of veterinary medicine, University of Calgary, says the biggest difficulty for many producers, their veterinarians, and even some university faculty is sorting out the various recommendations. “When talking about what we have to do in order to help a calf develop adequate immunity, we have to realize that one size does not fit all. When I started out as a veterinarian in northeastern Alberta, calving began the end of January — because those people were farmers.” They calved early, when they weren’t busy in the fields.

“That’s a completely different situation than ranchers, who usually calve in the spring. Anyone making a living with cattle will usually calve later, if they can, when the weather is better. Then, you don’t have to use barns and have cows confined, exposing them to possible dirty conditions. This is a huge change now, in Western Canada, with more ranchers moving to later calving — except for some purebred producers who feel they need calves born early so their young bulls will be old enough to sell as yearlings. They still fight the winter weather, or they do a complete about-face and have a group of cows that calves in the fall,” he explains.

photo: Supplied

So the first thing to consider when looking at the importance of calf immunity is the level of disease risk.

“The second thing is that research coming out of many different places is showing that we can vaccinate a baby calf and the immune system remembers — even though the calf already has passive immunity from mama’s colostrum. You can do early vaccination two ways — intra-nasally to create a local immunity (which in some cases will actually stimulate humoral immunity) or systemically,” says Janzen.

“When calves are very young, antibodies received from colostrum will interfere with the calf producing antibodies,” says Acton. “Earlier thinking was that vaccinating a very young calf didn’t do any good because of the maternal antibodies, but recently we’ve found that early vaccination does produce a cell-mediated immunity and also a memory. Then when you revaccinate that calf later, the second vaccination acts as a booster,” he says.

“The calf won’t get as much antibody production when vaccinated young — after he’s had colostrum — but he’ll get some cell-mediated response. Thus we can vaccinate young calves quite a bit earlier than we did in the past. We like to see all calves get a blackleg vaccine (generally in combination, like a 7- or 8-way vaccine) by about two months of age,” Acton says.

“At about the same time we are also using respiratory vaccines on these calves, such as modified live viral vaccines (IBR-BVD-PI3) in combination with bacterial pneumonia vaccine (pasteurella, hystophilus). This provides some protection against summer pneumonia, and gives an excellent base for fall boosters at weaning time. When producers give vaccines at or before weaning, the immune response is much higher and much better and more protective.” This really pays off in less sickness at weaning time, especially if the calves are weaned with minimal stress.

In some situations the calf will need local immunity, especially for things like intestinal tract disease. Most gut infections remain local (staying in the gastrointestinal tract) unless the infection goes systemic, with bacteria and toxins that leave the gut and get into the bloodstream to create acute toxemia. Some researchers have looked at the question of how to get a local immunity in the gut, to protect against scours. There are a number of problems that tend to be local, and systemic vaccines don’t give protection.

“Vaccinating is a challenge for some diseases, but the main principals are that if you vaccinate a baby calf — even at day one, in the face of passive immunity — when you revaccinate at weaning, the body remembers,” says Janzen. Vaccination at weaning time acts as a booster.

“Some producers ask about this because they’ve decided to not brand anymore, and if they are not going to brand, when should they vaccinate? They wonder if they could vaccinate soon after birth, at the same time they are tagging calves and putting bands on the little bulls. So I ask them what they are going to vaccinate for, and what time of year they calve. Many of these folks are calving later, during good weather. They don’t use corrals or calve behind the barn. Their risk of intestinal diseases (scours) in young calves is considerably lower,” says Janzen.

“Probably the only thing those calves are truly at risk for is clostridial diseases like blackleg, malignant edema, redwater, perfringens, etc. They all cause acute and highly fatal diseases. The risk for clostridial infections is always there. For most calves, this is still the most important thing we need to vaccinate for,” he says.

In community pastures, however, calves may be at risk for respiratory diseases (summer pneumonia). “When I was in Saskatchewan, in our community pasture system I noticed the calves were at risk for respiratory disease after they’d been presented to the pasture on ‘take in’ days. If those days were dusty, for the next month stock attendants would notice and treat calves with respiratory disease,” he says. The dust and stress made the calves more likely to become sick because dust irritates the respiratory passages, clogs the lining and covers up the natural defense mechanisms in the airways.

“I looked at that problem, based on 10,000 pairs placed in community pastures, and those were probably the only years those calves were at risk for respiratory disease if the ranchers were calving later. It was recommended that these calves be vaccinated for respiratory diseases, and the pharmaceutical companies pushed this recommendation without differentiating between the different types of operations,” says Janzen.

Most ranchers still think in terms of traditional branding-time vaccinations, even though many calves may not need to be vaccinated at that stage of their life, if they are no longer born during the stress of winter (cold weather, confinement in barns and corrals). The two things that stress calves the most and create the most risk for disease challenges are early calving, and commingling of calves at auction yards when they are sold.

“We’ve had a graduate student looking at auction markets in Alberta. In some areas, especially southern Alberta, she estimated that between 15 and 18 per cent of calves avoid auction barns completely. Those calves are sold in video auctions on the internet, for later delivery, and pre-vaccinated before shipping. The ranchers take the trouble to round them up and vaccinate ahead of weaning, according to their veterinarians’ instructions. If the calves were vaccinated in the spring when they were born, this vaccination at weaning time acts as a booster and is very protective,” Janzen explains.

Having calves preconditioned (vaccinated, weaned) before they leave the ranch has become a good marketing tool and strategy for these ranchers.

“Often these calves are referred to as winter-placed calves and are considered to be at lower risk than calves abruptly weaned and sold. They have some immunity already and haven’t commingled with other cattle at an auction yard.” They go directly from their home environment (where they were weaned with very little stress) to the feedlot, and stay healthier.

“Some of the animal welfare groups, looking at what’s best for calves in our livestock industry, are actually more concerned about commingling of different sources (including auction yards) than about various procedures like dehorning and castrating. I remember looking at pens of bawling calves at a feedyard where there were 300 calves in a pen. Looking at the sales tickets, those calves may have come from as many as 100 different original owners. It’s common to have health problems in put-together pens of cattle. Anything we can do as an industry to circumvent commingling of calves will be helpful.” This goes back to how they are managed and vaccinated initially.

“Cattle producers might use different vaccines under certain conditions, taking the principals of risk into consideration regarding when to vaccinate. If you vaccinate a baby calf you may not get a strong titer, but you’ll get enough response to provoke the immune system into remembering that in the fall when you vaccinate that calf again,” says Janzen.

When calving in cold weather, cows are confined where they have windbreaks and bedding, and calves must be protected from freezing so they are put into the barn. In this situation, you increase the risk of neonatal diseases, and have to become more intense and careful in your management — including vaccination — to make sure calves don’t get sick during the first days and weeks of life.

“There are a couple of intranasal respiratory vaccines that can be used, depending on the area and the individual operation,” says Acton. “For herds that are winter calving, or purebred herds with higher-value calves, or a commercial herd with a history of baby calf pneumonia (getting sick at about six weeks of age), these intranasal vaccines have been very helpful. They are easy on the calf, and because they are given intranasally they are producing an IgA response right where it is needed — locally, in the respiratory tract. We are using those in some of the winter-calving herds that might be more confined and show a history of risk for early respiratory disease in young calves. We give these intranasal vaccines when the calves are a day or two old,” he explains.

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