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Newborn calves gain temporary (passive) immunity against many diseases when they ingest colostrum from the dam�since this �first milk� contains maternal antibodies. After a few weeks or months this temporary protection begins to wane, however, and calves must build their own immunities. Vaccinating calves at the proper time can help protect them until weaning age and also help give them a good foundation for health as adults. Vaccinating calves too young, however, may not stimulate much immune response. If the calf still has maternal antibodies in his system, these tend to interfere with building his own immunities. The immune system sees no need to respond.

Dr. Chris Chase, Veterinary and Biomedical Sciences, South Dakota State University, says there are several considerations that producers need to keep in mind. �When maternal antibody protection begins to wane, we can probably get a good response to vaccinations by about three months of age. It all depends on how much protection the calf received at birth (how much colostrum, how soon�for maximum absorption of antibodies�and how good it was). In most herds, you won't find 100 percent of the calves fully protected; it's more like 70 to 80 percent. When developing calf vaccination programs, we need to know what disease problems are going on in the herd,� he says.

If it's a herd that has had issues with BRSV (bovine respiratory syncytial virus), for instance, this will necessitate a different plan than if the herd has not had problems. �BRSV is notorious for having maternal interference at low levels that can last for a long time,� says Chase. If the calf received some antibodies against BRSV from colostrum, the calf may not gain much immunity from an injected vaccine (unless it is adjuvanted) until those maternal antibodies are gone from his system.

�Producers need to have a plan for their own situation. There are many protocols and you might decide to give your calves vaccinations for IBR and BVD, but in reality those two diseases are generally not an issue in young calves,� he says. You need to be more concerned with these diseases as calves approach weaning age.

�Some herds, however, have trouble with pneumonia in young calves, and BRSV is a problem. In these cases you can use the intranasal vaccine,� says Chase.

�The intranasal vaccine does have the ability to get around maternal antibodies. The other thing a producer can do is use an adjuvanted vaccine. In most cases people think that only an inactivated vaccine is adjuvanted, but we do have some adjuvanted modified-live vaccines,� he explains.

�If we know we have a pneumonia problem in nursing age calves, BRSV is usually the culprit. There's no vaccine just for BRSV, however. You have to use the combination product containing BRSV-IBR-BVD-PI3, even though at this age in calves the BRSV is the only thing you are really worried about,� he says.

�Producers need to know what they are dealing with. There are some tests, using deep pharyngeal swabs and some other ways to get material from deep in the back of the throat, to get a more accurate diagnosis,� he says. A diagnosis is important, to know what diseases should be included in a vaccination program.

�At this point in time the intranasal vaccine will give the most likelihood of success and the least likelihood of failure, in that age group. From 2 weeks up to 3 months, this makes the most sense, particularly if you are worried about BRSV. The adjuvanted modified-live vaccine, where you give a single dose, also has some usefulness, but I haven't seen enough data yet in young calves with agents other than BVDV,� he says.

For calves, depending on what the producer must deal with, there are also 7 and 8-way clostridial vaccines that can be given at this age. �The interesting thing with these is that the literature tells us that if there are maternal antibodies present these might not work, but field experience shows that those vaccines definitely have some efficacy. This is especially true if you are looking at C. perfringens in young calves, or blackleg,� he says. You can vaccinate a calf at birth and still get some benefit.

�You can give these vaccines and not have to worry about problems with maternal antibody interference. Part of the reason is that with Clostridia we are actually vaccinating against an exotoxin. This is a simpler antigen, and easier for the immune system to see and attack, compared with some of the viruses (and all the processes that must happen to protect against those),� explains Chase. If a producer is having problems with enterotoxemia, for instance, calves can be vaccinated at a very young age, even if the cows were vaccinated during pregnancy (to stimulate high levels of maternal antibodies in the colostrum).

As a rule of thumb, most western ranchers give calfhood vaccinations at branding time. �When vaccinating calves at this age, the goal is often just to prepare them for whatever they will encounter at weaning time,� says Chase. It's like a set-up vaccination that will then be boostered at weaning. If you want to give a vaccination just prior to or at weaning, it's good to have this initial shot at an earlier age. On a farm that doesn't brand, just pick a time when calves are about three months old, to vaccinate them. Then the vaccinations given at weaning time act as a booster.

Maternal antibodies tend to interfere longer with some of the viral diseases, compared with some of the bacterial infections that create toxins. �The viruses are big proteins and have to be broken down and processed by the immune system in order to be fully recognized and attacked,� he says.

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