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FORT ATKINSON

If a dairy calf is the epicenter of a constant battle, then vaccinations are the heroes in the fight to defend her against the vicious attacks of bacteria, molds, viruses and parasites that are trying to infect her body and end her life.

Vaccinations are used to stimulate a calf's immune system, Dr. Amelia Woolums, Mississippi State University College of Veterinary Medicine, said during the February Hoard's Dairyman webinar sponsored by Dairy Calf & Heifer Association.

The presentation was co-hosted by Steve Larson, Hoard's Dairyman, and Dr. Mike Hutjens, University of Illinois.

A calf's immune system has two important features. It involves an innate immune response that is immediately and always active. It doesn't improve with repeated exposure, but that's not a problem in the case of a small cut or minor infection.

Her immune system also has an acquired immune response. It takes several days to several weeks to be fully active and it has memory, meaning it improves with repeated exposure. 'This is the target of vaccinations,' Woolums said.

The components of an immune response are B cells, which produce antibodies, and T cells, which act as hit men to kill infected cells and as generals, telling other cells what to do. 'When we vaccinate, we are telling the immune system to make more B and T cells,' she explained.

Whatever the vaccine, the B cells will make antibody to it and the T cells will be primed to kill it. When the calf is later exposed to an infectious agent, the B and T cells will be there, ready to fight it off.

Immune development

At birth, a calf has no antibody in its bloodstream and its immune cell responses are slower and lower than an adult cow's. 'Immune response of the newborn calf is functional, but it is naïve and immature,' Woolums said. 'Colostrum tides the calf over until the immune system matures.'

That means adequate colostrum intake is absolutely critical to calf health. Calves that don't receive their fair share are more likely to develop disease, more likely to die, and more likely to fail to reach their potential, Woolums pointed out.

'No vaccine is as good as getting enough good quality colostrum. I mean that with all my heart,' she said. 'Before anything else, excellent passive transfer is required to establish the basis for strong calf immunity.'

Calves with adequate colostrum intake will have high levels of maternal antibody. Vaccination in the face of this maternal antibody (IFOMA) has traditionally been considered ineffective, Woolums said, but research is building the case that calves sometimes respond to vaccinations.

Quite a bit of research shows that vaccination IFOMA can prime for memory response when maternal antibodies are gone, she said, and can prolong antibody titers.

When vaccinating calves, it is very important to remember that blocking is greatest in the first month of life. Boosters are especially important when vaccinating calves under six months of age, Woolums said, advising two doses about one month apart. Try to time the second (booster) dose two to four weeks before disease exposure is expected.

Intranasal vaccines, which are squirted into the nose for respiratory immunity, may be superior to injectable for calves with maternal antibody.

'They may not be blocked as much and may be best for calves under one-month-old,' Woolums said.

This delivery system is available for BHV-1, PI3V and BRSV. 'The downside is the duration of immunity may be short, especially for BRSV, so if you give intranasal, you may need to give another dose,' she said.

The list of vaccines available for dairy calves is long. 'In deciding which vaccines to use and when to give them, it's very important to talk to your veterinarian because he knows your herd the best,' Woolums advised.

When vaccines fail

It's important to keep expectations realistic. Vaccines rarely prevent infection completely and rarely prevent disease in all vaccinates.

'Respiratory vaccines decrease disease and improve productivity sometimes,' Woolums explained. 'They should be viewed as a tool to limit disease and not necessarily to prevent it.'

There are many causes for a vaccinated animal to get sick. 'Be sure to discuss disease in vaccinated cattle with your veterinarian to determine the most likely cause of the vaccine failure,' she said.

The problem could be related to vaccine administration. The MLV vaccines might have been mishandled. They might not have been kept cool and in the dark, preferably in a cooler with the lid on, or they might have been previously reconstituted. 'You can't mix them up today and use them tomorrow,' Woolums noted.

Another factor can be the disinfectants used to clean multidose syringes. Use just good hot water for cleaning needles, she advised.

Vaccine failure can also be caused by poor timing of administration. The animal might already be incubating the disease or no booster was given when it was needed.

Besides being already sick, the vaccinated bovine might have a nutritional deficiency. 'Animals not getting enough to eat will not respond properly,' Woolums pointed out.

The vaccine given and the actual pathogen exposure should also be considered in failure cases. The animals might have been infected with agents not included in the vaccine given or infected with strains of pathogens not in the vaccine.

In some cases, the challenge was overwhelming because of management problems. Even the best vaccine will come up short against bad air quality or overcrowding, so address any management problems to give vaccines the best chance to work, Woolums advised.

Important points for vaccinating calves

Calves are even more likely than adults to require booster vaccines, which should be given two to four weeks after the initial vaccination. Time the last dose to occur two to four weeks before disease is expected.

For instance, if calves raised in hutches are moved into group housing at eight weeks of age, give them boosters no less than two weeks before the move.

Case in point

Woolums consulted for a dairy milking 1,600 cows that had a problem with pneumonia in calves when they went into group pens at four weeks of age. There were 25 to 30 calves per pen and computerized feeding.

Fifty percent of the calves had been treated from pneumonia in the past month and five out of 200 had died.

Since the month-old calves should still have been protected by colostral antibodies, Woolums checked colostrum delivery via total serum protein on week-old calves and found the calves did not have an adequate rates of passive transfer. It was lower than the desired minimum of 5.4 in no less than 80 percent of calves.

Focusing on calf care in the hutch, Woolums found the youngsters' body condition was also lacking. 'We want them in great health, but because of miscommunication, the calves were getting only four quarts rather than six quarts a day,' she shared.

A review of the farm's vaccination plan also showed the calves were getting intranasal IBR/Pl3 at two days of age. That is likely to early with a good colostrum feeding program, won't protect for long and does not include BRSV, which is very important in fighting off pneumonia. 'I'm not sure that can really help. I personally would move out to 2 weeks old,' Woolums said.

The calves were also given intramuscular five-way at the move to group pens. 'That's more viruses, which is good, but giving it right before turnout doesn't give the calves time to respond,' she pointed out. 'It would be better to give it two weeks earlier.'

However, since the maternal antibody at two weeks of age may block an injectable vaccine, she suggested the farm use intranasal at that time, then boost with intranasal right before going into the group pen.

Since it's hard to prevent respiratory disease at one month of age with vaccination before then, she advises focusing more on management to prevent pneumonia in these very young calves. Target better colostrum, nutrition and air quality, and house calves in groups of eight to 10, if possible.

'Vaccination is a valuable tool, but it can't do everything alone,' Woolums said. 'It needs good management.'

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