A Breeder’s Veterinary Perspective

Biography:

Dr. Colin Palmer is an Associate Professor of Theriogenology (Animal Reproduction) at the Western College of Veterinary Medicine. Originally from Nova Scotia, Dr. Palmer worked in mixed practices in Ontario and British Columbia and has owned/operated a practice in Saskatchewan. Dr. Palmer along with his wife Kim and children Lauren, Emily and Carter run a herd of purebred Red Angus cattle under the KC Cattle Co. name.

Vaccines are a priceless tool for modern livestock production. They are as important to the economic viability of a cattle operation as pesticides are for crop production. Rabies, Blackleg, IBR (Infectious Bovine Rhinotracheitis), BVD (Bovine Viral Diarrhea), anthrax, bacterial and viral respiratory infections, and numerous other diseases are prevented or lessened in severity because of vaccines. Over the last couple of decades new vaccines have been developed for calf scours, mastitis, and foot rot prevention; however, no less revolutionary has been the improvements with each generation of product targeting the same ol’ cattle diseases that have been with us for decades.

Disease causing infectious agents are usually a bacterium or a virus. Germ is a commonly used word for bacteria and viruses; especially ones that cause disease. Molds (fungi) are less commonly involved unless conditions are right to allow their numbers to flourish. Ringworm is a common skin condition in cattle and other livestock caused by select species of ringworm fungi. Parasites are also infectious, but most prefer to quietly steal to survive rather than to cause overt harm. A notable exception might be the coccidia parasite responsible for the bloody diarrhea associated with coccidiosis in cattle. Several types of very small organisms (aka. microorganisms, microbes), mostly bacteria, live within our bodies and are beneficial causing no harm whatsoever. Many of these bacteria assist with digestion, help produce essential nutrients and assist the immune system in the destruction of harmful organisms. The mix of organisms, called a microbiome, residing on our skin, in our noses, in our gut and virtually any where in our bodies is unique to that system and to the individual. A microbiome is not static. Antibiotics, foods we eat, others we come in contact with, where we live, who are parents were and numerous other factors, many of which we are just now learning about, can all influence a microbiome. Newer technology, such as PCR (polymerase chain reaction) tests, have proven to be much more sensitive for identifying organisms in environments that were previously believed to be sterile. Older testing methods relied on culture, which essentially meant that these organisms had to grow in a petri dish under the right conditions, or at the very least had to be detectable by testing methods that required the organism to remain intact. When an infectious agent enters a body, it will move to its preferred site where it will reproduce; provided it has entered through the right system. For example, the gut, respiratory system, or blood. Respiratory pathogens that don’t get inhaled may simply desiccate or dry out on the skin surface. An important concept for understanding disease treatment and prevention is recognizing the difference between viruses and bacteria. Both are tiny, yet viruses are smaller than even the smallest bacterium, only visible with highly specialized microscopes. Bacteria are living, single-celled creatures with an outer protective cell wall and an inner lining protecting the cell’s organ structure. Bacteria can produce their own food and can thrive in a wide variety of environments. Bacteria tend to be opportunistic, feeding on biological debris that is present often from physical damage (cuts, wounds) or damage caused by viruses. Viruses consist of just a thin protein coat covering a small amount of RNA or DNA that represents the genetic code necessary for creating future generations.

To multiply, viruses must attach themselves to living cells taking advantage of their host’s infrastructure. Most viruses are very specific about the types of cells they prefer. For example, blood cells, cells lining the gut, or specific cells within the respiratory tract. Because they can’t reproduce on their own viruses must reprogram the cells they attach to to allow themselves to replicate. Unlike bacteria, viruses invariably behave like pirates exploiting their host cells until the cell dies or bursts. Some viruses may even turn normal cells into cancerous cells. Antibiotics target bacteria, not viruses. Antibiotics have been used to fight disease even when it is known that the cause is a virus with the belief that the antibiotics would help fight a secondary, opportunist bacterial infection, thereby lessening the severity of the disease or even saving the life of the patient. Such use of antibiotics is discouraged in most situations as it contributes to antimicrobial resistance and the development of so-called super bugs. Drugs designed to specifically target viruses seem logical but there are very few antiviral drugs available. Generally, antiviral drugs have a very limited spectrum of use. Our best defense against viruses is prevention of infection and one of our best preventative tools is vaccination. When viruses invade and start to multiply this is called an infection. Left unchecked the virus will proliferate, and symptoms of illness will appear. The earliest symptoms such as fever, headache, tiredness etc. are a direct result of the body’s defense mechanism, the immune system, kicking into action. Fever is not just a sign - a higher body temperature may limit the reproductive capabilities of the invader. The body’s immune system is very complicated and consists of a few modes of defense. The first line is relatively nonspecific; designed to attack anything foreign. Blood consists of oxygen-carrying red blood cells and white blood cells, also called immune cells. There are different types of white cells all designed to fight infection in different ways. Many types of bacterial infection are associated with pus production. The most predominant white blood cell found in pus are neutrophils which can migrate from the blood vessels to site the site of infection where they surround and kill the invaders. Other, larger cells called macrophages swallow up viruses and broken-down cells leaving behind recognizable parts of the invaders called antigens. B- and T- lymphocytes are another closely related class of white blood cells. T-lymphocytes attack infected cells in the body; however, they are capable of much more targeted attacks then macrophages. T-Lymphocytes may also produce a subclass of themselves called “memory T-cells” which will remain in the body for a period of time ready to defend against that same invader should reinfection occur. T-cells play the predominant role in what is called cell-mediated immunity. B-lymphocytes produce antibodies, also called immunoglubulins, which are large Y-shaped proteins designed to recognize specific antigens (recognizable groups of protein) on the invaders, bind to these antigens, and then interact with other components of the immune system to destroy the invader. Like T-cells, a portion of B-cells will become “memory B-cells” surviving in the body ready to make fresh antibody when the time comes. We all recognize the importance of colostrum to calves, and it is the ready-made antibodies present in colostrum that are absorbed by the calf to help it fight all sorts of infections until it is capable of making its own antibodies. All vaccines are made from taking a piece of the bacteria or virus and modifying it so it will stimulate the production of memory T- and B-lymphocytes that carry forward the ability to fight the invader in the future. Different types of vaccines work in different ways. The diversity of bacteria and viruses dictates that one type of vaccine or vaccine technology is often effective for only select group of organisms. Following vaccination it usually takes a few weeks for the body to produce enough memory cells to offer protection in case infection occurs. Fever and mild sickness are normal – it means the immune system is responding to the vaccine. In most cases, second (booster) vaccinations are required to confer an effective level of immunity with boosters required thereafter at regular intervals. Vaccine manufacturers study the response to vaccines to determine when and for how long an adequate level of protection is sustained. Historically, levels of circulating antibody were measured. Another method involves studying actual disease challenge scenarios. Scientists have recognized that antibody levels may not tell the whole story and a great deal of energy is now being focused on the role of memory cells. Immunology is a very prolific field of scientific study that has made some significant gains over the last few decades. Many of us owe our lives and livelihoods to the breakthroughs that have been made.