Cattle producers often ask Penn State extension veterinarian Dr. Hayley Springer what to include in a vaccination protocol. Since farms have a variety of management challenges and different vaccine protocols, the answer is “It depends.”
Springer said the definition of the word vaccinate is “to administer a vaccine, usually by injection.”
“The goal is not just to inject a product, but to increase resistance to disease,” she said. “Rather than asking ‘How should I vaccinate my cattle?’ the producer’s question should be ‘How should I immunize my cattle?’”
To introduce vaccination concepts, Springer explained immunology basics. “There are three main types of vaccines,” she said. “Modified live vaccines are a live virus. The virus is attenuated so it can’t cause disease. Killed virus vaccines have the virus, but it’s completely dead. A subset of modified live is intranasal vaccines.”
Each type of vaccine works differently. “Antibody immunity is the classic vaccine immunity, but there’s also cell-mediated immunity,” said Springer. “In addition to antibodies providing protection, immune cells provide specific protection against a pathogen. A specialized type of antibody, IgA, provides mucosal immunity.”
A modified live vaccine administers a very small dose of the virus itself. “We expect that the modified live organism is going to proliferate,” she said. “It will then interact with immune cells, called B cells, and produce antibodies.”
Modified live vaccines also produce immune memory, so when the animal is exposed to the pathogen, its immune system responds more quickly and strongly.
One of the unique aspects of a modified live vaccine is that cells become infected, which interact with T cells that make natural “killer” cells that attack the pathogen. “Now we’ve paired faster, stronger antibody response with attack cells ready to fight that pathogen,” said Springer.
Killed virus vaccines provide a larger dose of the actual virus. A killed virus vaccine has less “memory” and is not disease-protective after one dose.
“We give a second dose,” said Springer, “and now we have the full-blown memory response and the faster/stronger response.” Because it’s a dead virus, cells are not infected and there is no cell-mediated immune response. The antibody response is present after the second dose of vaccine.
Intranasal vaccines are modified live vaccines with unique characteristics. “There are M cells in the lining of the respiratory tract,” said Springer. “The virus [in the vaccine] binds to the specialized M cells to get IgA, which specifically controls mucosal surfaces. Now there’s an antibody in the noses of calves, ready to react as soon as they see the pathogen.”
An important vaccine consideration is lag time – when protection begins and how long it lasts. “Remember there is always a lag time and the calves are not protected the day we vaccinate them,” said Springer. “We’ve vaccinated, but we’re trying to reach immunity.”
The lag time for a modified live vaccine is typically two to three weeks. “From the time we give it to the time of peak protection is 14 to 21 days,” she said. “We can leverage that by giving it so protection peaks when the calf is most likely to be stressed and/or exposed to disease.”
Because killed virus vaccines require two doses, the lag time is 28 to 42 days, which means careful planning is essential. An intranasal vaccine can provide immunity in seven to 10 days, but protection wanes after two to three months.
Effective immunization requires vaccine virus replication. “Previous vaccine or disease exposure along with maternal immunity can inhibit vaccine virus replication,” said Springer. “If we put a modified live vaccine in an animal that has strong immunity or maternal immunity, we may not get full replication of the virus, and may not get full immunization.”
Calves that do not have sufficient maternal immunity from colostrum suffer from failure of passive transfer (FPT), which often manifests as diarrhea or other illness, and sometimes death. “Every time we have a failure of passive transfer, it adds up to about $85,” said Springer.
The best colostrum is from the cow, but colostrum replacers are available. Shelf life for colostrum replacer is quite long. Springer said colostrum replacer should be bovine colostrum-derived and contain 150 to 200 grams of IgG. If IgG levels in a product are lower, she advised giving higher amounts.
For calves that receive sufficient maternal immunity from IgG, the challenge with vaccine timing is not getting a good antibody response or a good cell-mediated immune response. However, if protection against respiratory disease is required, an intranasal vaccine is appropriate.
“We don’t want to vaccinate young calves that have good passive transfer unless it’s with an intranasal vaccine,” said Springer. “Calves with FPT don’t have maternal immunity, so if we know the calf doesn’t have passive transfer, we can vaccinate earlier because they won’t be impacted by maternal immunity.”
Vaccine history can be an issue with immunization programs. Springer encouraged those who purchase young calves to know their vaccination status to obtain strong immune responses when vaccinated. “We can use intranasals, but is there value in it?” she posed. “If I buy a calf and know it has a good vaccine history, why would I pay for that if the calf is already protected?”
Stress plays an important role in calves’ immune response. Calves with physiological and/or psychological stress may be immunocompromised and may not develop an effective immune response when vaccinated.
“Cortisol is the stress hormone and shuts down the immune system,” said Springer. “If we give a vaccine to a highly stressed calf, it isn’t going to have the same effect as if we give a vaccine to a calf that is not stressed.”
Factors that induce stress include weaning, handling, weather extremes, diet changes, hauling and commingling.
Springer suggested reducing stress or vaccinating before stress or after stress. “We can spread out stressors,” she said. “A calf can be vaccinated then sent back to its mom. We might re-vaccinate before weaning because post-weaning is when we see respiratory disease. Avoid vaccinating in the immediate post-weaning time – it’s a huge transition and stressor for calves.”
Springer said, “In an ideal world, I’d start with a well-vaccinated dam so the colostrum is good quality. Make sure the calf gets up and suckles right away so it gets colostrum and have colostrum replacer on hand.” If early protection is necessary, use an intranasal vaccine.
She said a basic calf vaccination program should include a five-way respiratory vaccine and a clostridial. “What else you add depends on the situation,” she said. “I recommend working with your vet to determine exactly what you’re going to give.”
by Sally Colby