Stress in the Life of a Horse. Part IV of a Six-Part Series

In Part III of this series, we discussed the amazing immune system and its lines of defense.  The ‘first responders’ provide immediate defense in a non-specific way.  These are the physical barriers of skin, saliva, tears, and the linings of the intestinal, respiratory, and reproductive systems, as well as immune cells and other complementary proteins and cytokines. 

Behind these front lines is the acquired immune system that creates immunological memory.  This is the science behind vaccination.  After it has responded to a pathogen (harmful invader), the acquired immune system remembers that pathogen and stores the information in a data base so that the next time it is encountered, the immune system can send a specialized rapid response team, called antibodies, to target that particular pathogen.

Stressors at any age or stage in the life of a horse can cause an unbalanced immune system, but certain times in their lives are more critical than others.

The First Days of Life

In the very earliest days of life, foals are challenged by a lack of immunity.  Because there is no transfer of immunity via the placenta, the foal 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 antibodies is crucial, and can occur in a short window of the first 24 hours of life for maximal absorption.  During that window, the newborn’s stomach remains porous, so that large proteins such as antibodies can pass through the stomach wall.  But even in the best of circumstances, the foal, during the early weeks of life, remains susceptible to disease while its own immune system is getting ‘educated.’

Pregnancy, Foaling, and Lactation

Pregnancy itself is a time of major stress for the mare.  She not only has to deal with the usual stresses of everyday life, but also the hormonal changes, the developing foal, and the preparation of the mammary glands to produce milk.

After her eleven-month gestation, when the mare gives birth, her body undergoes dramatic changes, and lactation begins.  Pregnancy, foaling, and lactation all put the mare under stress, causing more frequent episodes of stress-induced immune system activation causing inflammation.  Her body’s demands for nutrients increases dramatically as she nourishes her growing baby, causing further stress and an increased risk for invading pathogens. 

The Equine Athlete

During his/her sporting life and competition seasons, the performance horse, though born to run and compete, can experience the stressors that go along with a demanding training regimen, changes in feed or schedule, trailering, and competing.  These events can and often do call the immune system into action to respond to stress, and may cause collateral inflammation.  The horse can become moody and less willing to train, may experience a decrease in appetite due to intestinal discomfort, or may exhibit a shortening of stride due to muscle soreness, all of which can affect performance in the arena.

The Senior Horse

The older, senior horse tends to have an unbalanced immune system simply from the effects of aging, increasing the likelihood of getting sick, and slowing the recovery from disease or injury.  As the horse’s athletic ability diminishes with age, riders and trainers need to make accommodations in the training regimen, and to minimize stressful situations. 

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 bodily system (ie, muscular, digestive, respiratory), and not over-react where it is not needed.  The body usually does a good job of keeping the immune system in balance.  

This amazingly complex system is a valuable ally in keeping the horse healthy and comfortable, and keeping the system functioning properly is critical to helping them thrive.  In 2014, an orally dosed bioactive protein was introduced to the equine market.  This product, marketed as LIFELINE® Equine Performance Supplement, by supporting a normal immune system, has shown measurable success in addressing issues of muscle soreness, joint pain, respiratory problems, and nagging digestive upsets.

Reducing the negative effects of stress is clearly beneficial to the horse, no matter the life event that triggers them; and LIFELINE® has demonstrated success in doing so.

Next week, Part Five will examine how the body systems of the horse react to stress.