Why do some calves fall ill, despite good management and others don’t? That was the question answered by Derek Foster, DVM, PhD, College of Veterinary Medicine at North Carolina State University, in a presentation titled, “Vaccinations, Immune Function and Salmonella Vaccine Research.”
“The immune system has constant exposure throughout life to pathogens, like viruses, bacteria, fungi, protozoa, and GI parasites,” Foster said. “It’s a pretty tough job to recognize all these things.”
He explained that the immune system has to recognize both good and bad elements entering the body through the eyes, respiratory system, oral/GI route, openings in the skin, reproductive and urinary system, blood stream, liver and mammary gland.
He divided the immune system into two categories, though he added that the two interact considerably: innate mechanisms (what a creature is born with) and acquired. Although farmers can’t change the innate aspects of immune system, the acquired can be made stronger through vaccines.
The innate immune response is always “on duty” to respond first to threats. It’s not specific to a pathogen and it does not improve with time and exposure.
Acquired immune response may take days or weeks to become fully activated, but it specifically targets a pathogen and with repeated exposure, improves its strength and speed of response.
Foster likes to compare the innate immune system as the body’s “infantry” against threats to the barriers of abomasal pH, skin and mucus; soluble factors of antimicrobial proteins in mucus and other fluids; and cells that provide surveillance and defense in tissue and blood.
Like soldiers, “they respond quickly in almost any body system to any pathogen,” Foster said. “It amplifies the response to increase the response and recruits specific responses from the acquired response.”
Some of these responses can damage the animal, however.
The acquired immune system is more like “special forces” soldiers “called in by the innate immune system to target specific pathogens,” Foster said.
Vaccines and previous exposure to the pathogens provide the “special training” to these “soldiers” to fight disease. They include antibodies, “helper” cells that amplify and direct the response, and “cytotoxic” cells that directly kill infected cells.
Some calves’ innate immune systems are weaker than others; however, producers can mitigate this effect, which can be especially important during the youngster’s first several weeks of life.
To maximize calf immune function, Foster recommends offering one gallon of high-quality colostrum within four hours of birth, ideally, fresh from the calf’s own dam. If not, the second-best option is fresh from another cow. The next-best choice is frozen colostrum, followed by powdered replacer.
In addition to colostrum, spacing out stressors can help mitigate their effect on a calf. For example, de-horning, weaning, moving to a new pen, excessive heat or cold, and meeting new caretakers can all stress a calf.
“A calf’s immune system is slower, weaker, and less specific,” Foster said.
It’s also important to use sound operating practices.
“If there’s salmonella everywhere, it won’t matter what else you do,” Foster said.
He referenced a farmer in Colorado that had numerous surfaces all over the farm testing positive for salmonella and the calves were exposed upon birth. The animals had little hope of avoiding the disease, especially at such a young age.
Vaccinating also helps calves better cope with potential illness, especially once the colostral antibodies diminish, which is at about three to four months.
Foster said vaccines can include killed pathogen, modified live/weakened pathogen or a specific part of a pathogen. Foster said a modified life strain of vaccine offers the best protection, but it bears an increased risk of side effects.
Foster said vaccines affect the immune system once they’re recognized by a surveillance cell and carried into a lymph node. This triggers a response from the body that is amplified upon second exposure, creating “memory” cells that stay in the lymph nodes and in tissues around the body to rapidly mount a defense in the future.
Foster said vaccinating dry cows improves immunity in neonatal calves.
“It provides specific antibodies for pathogens in neonatal calves,” Foster said.
Though he called it a “slow way to fix the problem, it’s helpful for long-term control.”