As explained in Part I of this series, the immune system is a complex and multi-layered network designed to defend the body against foreign "invaders" such as viruses, bacteria, protozoa and allergens, or against damage from injuries ranging from minor cuts to more traumatic events. The first layer is the innate immune system which consists of physical barriers (skin, saliva, tears and the linings of the intestinal, respiratory and reproductive systems), as well as immune cells and other complementary proteins and cytokines. These "first responders" provide immediate defense in a non-specific way.
The second layer is the acquired immune system that creates immunological memory. This is the science behind vaccination. After having responded to a pathogen, the acquired immune system remembers that pathogen and stores the information in a "database" so that the next time it is encountered, the immune system can send a specialized response team, called antibodies.
Horses of all ages or stages of life can experience stressors that cause an unbalanced immune system, but certain times in their lives are more critical than others.
Foals, for example, receive no transfer of immunity via the placenta, and so must drink adequate amounts of colostrum (the first fluid the mare secretes from her udder after foaling) to absorb some of the mother’s antibodies. This oral transfer of immunities is crucial, and can occur because the newborn’s stomach remains porous for a short time. This means that large proteins such as antibodies can pass through the intestinal wall. There is a window of about two to four hours for maximal transfer of antibodies to occur. But even with this transfer of antibodies, the foal during the early weeks of life remains more susceptible to disease while its own immune system is getting "educated."
For the mare, pregnancy itself is a time of major stress. The pregnant mare not only has to cope with all the normal stressors of life, but also has to deal with hormonal changes, the developing foal growing inside her and preparation of the mammary glands to produce milk.
When foaling occurs there are dramatic changes to the mare’s body, and lactation starts.
Pregnancy, foaling and lactation are times when there are more frequent stress-induced events of immune system activation causing inflammation, and there are increased demands for nutrients to support the mare and her milk production to nourish her growing baby. Because pregnant and lactating mares can be more at risk for invading pathogens, careful attention must be given to minimize stress and ensure adequate nutrition.
Performance horses are born to run and compete and they need to do so, but there are times when they cannot for various reasons, and times when they must be reined in to keep them from overworking. Each horse is an individual, and some are better able than others to cope with stress events like a demanding training regimen, a change in feed or in the weather, trailering and competing. These events can, and often do, trigger stress hormones, one of which is adrenalin. Adrenalin increases blood flow to muscles for immediate support to perform difficult tasks, but while doing that, it reduces blood flow to other less urgently needed body systems like the digestive, respiratory and immune systems.
In the performance horse, too much stress can manifest itself in various ways. The horse can be moody and less willing to train, and may have a decrease in appetite. An over-stressed horse can also develop stiffness due to overuse of muscles, ligaments, tendons, cartilage and joints.
Old age is characterized by a state of chronic immune stimulation. The older, "senior" horse tends to have an unbalanced immune system, as do aging humans, making him more likely to get sick and causing a slower recovery rate from stress events like disease or injury. The senior horse's athletic ability diminishes as he ages, and riders and trainers need to make appropriate accommodation in the training regimen, and to recognize and minimize stress-related situations.
Research has shown that orally-dosed bioactive proteins such as LIFELINE AgeWell Performance Supplements can reduce chronic immune stimulation associated with aging.
The immune system of the horse can react in various ways depending upon the situation. When functioning normally, the immune system has a remarkable way of distinguishing how to react at a local area of the body, or over a specific system in the body (i.e. muscular, digestive, respiratory systems), and not over-react where it is not needed. The body usually does a good job of keeping the immune system in balance. This is a very efficient way to conserve nutrient use and immune system resources.
For example, if a horse gets a scrape or cut on the skin, both the circulatory system and the lymph system react by diverting their resources only to the area of injury. The same is true when a specific joint or muscle on one leg is injured or overworked; there is inflammation at that affected area, but not over the entire body.
The increase in blood and lymph flow to the damaged area causes redness and inflammation, while also delivering immune responders. Injured or damaged cells release histamines and other immune system messengers called cytokines that signal nearby undamaged cells to swell, which protects them from damage by invading pathogens. The immune system then reacts by sending extra defenders to the area to recognize and kill opportunistic invaders, and other responders join them to help remove damaged cells and stimulate new cell growth.
Orally-dosed bioactive proteins have been demonstrated to protect animals exposed to bacterial and viral infections. For example, mice with acute lung inflammation induced by exposure to a bacterial infection were able to more easily fend off the infection quickly. Anecdotal evidence from LIFELINE Equine Performance supplement users has shown that horses dosed with LIFELINE that are exposed to bacterial and viral challenges have reacted similarly; they either are unaffected by the challenge or return to normal health more quickly.
The amazingly complex immune system, plus assistance from orally-dosed bioactive proteins, are valuable allies in keeping horses healthy.
Author Pam Maley is an educator who, with her husband, co-owned and -managed a Thoroughbred broodmare farm in Lexington, Kentucky, where she was closely involved with all aspects of equine life. An avid former foxhunter, her journey with horses continues as a writer and editor with EquestriSol. This is the second part of her three-part series detailing Immune System Basics. Part I examined how the immune system works. Part III will detail the immune system reaction in the horse’s muscular, digestive and respiratory systems.