Better genetics After developing a skin test to measure immune response, research will focus on developing genomic test
RED DEER — A University of Guelph researcher has developed a simple skin test to measure the immune response of dairy cattle.
HIR Immunity+ is a patented technology that helps producers select for cattle with an enhanced ability to fight off diseases such as mastitis, Bonnie Mallard told the Western Canadian Dairy Seminar held in Red Deer March 11-14.
The next step is to develop a genomic test because disease resistance is heritable.
Genetic tests help producers select cattle with better production and growth, but disease immunity has been more problematic because there is inconsistency in diagnosing diseases such as mastitis, lameness and metritis.
“Maybe they are not getting any worse but maybe they are not getting any better either,” she said.
Mallard and her research team decided to study the immune system of dairy cows to see if that might be a pathway to reducing the incidence of disease with each successive generation.
Researchers classify animals as high, medium and low immune responders.
About half the disease found in dairy cows seems to occur in those with low immune response.
Those with high immunity also seem to produce better colostrum and respond well to commercial vaccinations.
Low responders get more disease, which is also more severe.
“You are best to make sure you are vaccinating cows that are going to respond and are going to respond well,” Mallard said.
In some cases, the low responders may need a double shot of vaccination.
Genetics research shows chromosomes nine and 23 have a tower of significant single nucleotide polymorphisms, which seem to be critical in governing immune response in cattle.
The need for antibiotics might be lessened if these cattle can be selected.
The genetics company Semex has the licence to use the technology to identify sires with an elite high immune response classification. These are marketed as Immunity+bulls, which should pass on the characteristic to their offspring.
There are three types of immunity:
- Passive immunity is initial and temporary. Antibodies from the mother are passed through the colostrum and protect the calf in the early months of life. It fades as the calf’s immune system starts to develop.
- Innate immunity is the first line of defence in mammals to protect them against harmful invading microbes. It is not long lasting but initiates adaptive immunity.
- Adaptive immunity is primed by the innate component. It recognizes a broad range of pathogens and remembers them from subsequent exposures. It gives a more rapid and greater immune response. It is specific and long lasting, similar to a single polio vaccine that lasts a lifetime.
“The immune system has a memory,” said Mallard.
Immune response is 25 percent heritable, compared to 25 to 30 percent for production traits and 15 to 40 percent for conformation.
“The genetic improvements you have been making to production traits and some of the conformation traits, you could expect to make the exact same rate of improvement for these immune response traits,” she said.
There is still no substitute for a well managed vaccination program, and producers can work with veterinarians to select a wide variety of treatments.
“There are dozens and dozens of vaccines for any given disease,” said Amelia Woolums of the University of Georgia.
Vaccination activates key players in the body.
A calf has no antibodies in its blood stream at birth and does not start to build disease immunity until it is five to eight months old.
Colostrum helps a calf get through this part of its life. A calf that doesn’t receive enough colostrum is at greater risk of becoming sick or dying.
A U.S. study showed 19 percent of calves did not receive adequate colostrum.
However, vaccines administered early in life may not be as effective if a calf received plenty of maternal antibodies and may actually block the benefits of immunization.
“Vaccines cannot do a better job than colostrum,” she said.
Producers who vaccinate calves younger than six months should give at least two doses one month apart. It is a good idea to consult with the herd veterinarian regarding vaccines and dose.
Woolums said intranasal vaccines might be more effective than injected vaccines in calves with moderate to high concentrations of maternal antibodies.
However, the immunity may not last more than a few months.
As well, more doses of the intranasal variety may not boost as effectively as repeated doses of injected vaccines.