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By Gary DiGiuseppe

Protection from mother's milk and an early vaccination can get your calves only so far in health.

Not all calves have the same level of disease protection when weaned, says Dr. Mark Spire, D.V.M. That's why booster vaccines are so important.

Spire, who is technical services manager for Merck Animal Health, says while Mother Nature's first line of protection of a calf is through its mother's colostrum, there can be a fair amount of difference in the levels of antibodies in that first milk.

"Colostrum is basically made up of all the antigens or pathogens that the cow's been exposed to during her lifetime," Spire explains. "Then the antibodies will be absorbed into the calf's gut within about 24 to 48 hours after it's formed."

There are 2 problems related to inadequate disease protection. One is only about 90 percent of beef calves get adequate levels of colostrum. Spire says lack of colostrum could be related to a previous case of mastitis in the mother. If the cow is still a heifer or is herself on a poor plane of nutrition, she could produce inadequate amounts of good quality colostrum.

A second factor could lie with the calf, such as a difficult birth or cold stress that prevents it from getting up to nurse very well. As a result, he says, "We're starting at a deficit in a set of calves. Not all of them are carrying the same level of protection."

Another problem involves the variability in the colostrum of each antigen, which stimulates the cow's body to produce antibodies. Spire says, "If a cow has been exposed to red nose (infectious bovine rhinotracheitis or IBR) or BVD, or to a pinkeye antigen or blackleg, that's what goes into the colostrum."

Those protections dissipate but at different lengths of time after a calf has nursed. Spire says IBR and BVD antigens persist longer than those of other viruses that are very short in duration. The antigen for blackleg, which is most often caused by the bacterium Clostridium chauvoei, may only last 2 months. So one by one, from the calves' birth to about 6 months of age, they are losing protection from each disease that they received from the colostrum.

At this point in time, says Spire, the calves have to achieve "active immunity" — they have to be exposed to pathogens so they can develop their own antibodies. This is most commonly done via vaccination.

"It's very common to take spring-born calves, around 2 months old, and vaccinate them for various diseases," he says. "The problem with that, since we have a mixed population of protected and unprotected calves, is the calves that are unprotected can respond pretty well to the vaccines, but the calves that are protected still have colostral antibodies there."

Those colostral antibodies block the vaccine so that it does not work as well as it should, so by the time the calves reach 4 to 6 months of age, the rancher again has a dilemma. "We still have a very vulnerable set of calves there, even though we think we've done the right thing and vaccinated them," Spire says.

Spire notes most vaccines state on the label that calves younger than 6 months of age should receive boosters. In some cases they're more specific, saying the boosters should be administered within a certain period after initial vaccination, perhaps 3 to 4 weeks after. The intention, he says, is to exact the maximum benefit from that particular type of vaccine.

Producers need to read the label and understand that for most vaccines given to calves aged 2 to 4 months, one shot doesn't fit all for all vaccines. Many require a booster by weaning.

It's important to remember that despite the availability of vaccines, calves are still going to be exposed to disease. Spire says, "Unfortunately, we can't just put a shield around them and protect them." Vaccination will reduce the severity if a pathogen does get into a calf, and it will also reduce the degree of replication.

"An analogy is when you get the flu. You may have had a low number of viruses that come in, but as the disease process goes on they replicate and your clinical signs get a lot more severe. Because of vaccination, the disease signs are a lot less."

A vaccinated calf protects other calves
A protected calf also will not shed virus in numbers as large as will an unvaccinated animal, and that reduces the potential for a massive disease outbreak in the herd.

"You may see some sickness, but it's not going to be severe. It's not going to last as long," Spire says.

Even if just 80 to 90 percent of the calves are protected and the rest are susceptible, the level of pathogens in the herd is suppressed enough to ward off a severe disease outbreak. "If we have colostrum in there, the calf then will use those colostral antibiotics to fight off the infection. But again, the calf does become infected; there's no impenetrable shield around him."

Boostering is also critical because it allows the rancher to know he or she has a base level of protection. Spire says, "At some other point in time — say weaning, in this example calf — when we revaccinate them, we get a really big jump in the immune protection level. With the first shot we will raise the immune level to a point, and then when we booster them we really kick that level up higher. That will be sustained for a longer period of time."

The level of immunity from a vaccine, and the length of time the immunity lasts, both vary. As a result, vaccinated calves can still suffer illness when the protection starts to wear off. Parainfluenza 3 (PI3) provides a short duration of protection, as does BRSV (bovine respiratory syncytial virus).

"We may only get 2 to 3 months' worth of protection out of those types of vaccines," Spire says, "whereas with the IBR (infectious bovine rhinotracheitis) or BVDV (bovine viral diarrhea virus) components, we may get months and months. We've shown up to a year of protection in experiments that have been conducted with those 2 particular viruses. So the closer we are to the time of vaccination and that disease exposure, the more comprehensive we see the protection level in those exposed animals."


Vaccinate on the calf's schedule, not yours

Spire stresses the importance of reading the labels and following the timing rigorously. He says, "Too often, we fit our vaccination schedule for a set of calves to our schedule. When the kids are home from school or when we've got the help to do it, we set that up, and that may not be the best schedule for a calf. And we tend to think one dose of a product fits all, and it doesn't. We really have to look at giving a second dose."

And, he says, it's important to understand the duration of protection, citing pinkeye vaccines as an example.

"Most pinkeye vaccines are designed to last a season, and the type of antibodies they build will last typically 4 or at the outside 6 months," Spire says. "If we work calves too far ahead of our typical pinkeye season, we'll end up seeing that these vaccines don't hold."
Pinkeye vaccine, he says, is the one that's most often misused in this manner. "People may want to give it in March or February. We don't see the fly numbers and the dust and the pollen counts then. It gets to August or September and people say, ‘I vaccinated that calf in March,' and all of a sudden in August they've got a pinkeye outbreak. And they say, ‘The vaccines should have worked.'" In this situation, timing of administration matters.

When selecting a vaccine or setting up a program for beef calves from birth to weaning, it takes some thought — thought about the type of vaccine to use, the need to use a specific type of vaccine, when to use it that best suits the calf, how long protection will last after use and whether the vaccine requires boostering to be most effective. A good vaccination program addresses those questions and others. One size doesn't fit all when it comes to herd-level protection.

"Give Calves a Boost" is from The Cattleman magazine's August 2013 issue.