Put a box in front of a cow, fill it with fresh grass, put a perforated
lid on it so the cow can’t eat, and watch what happens.
This simple experiment was used to detect stress in cows,
and it worked elegantly. All the
researchers had to do was look at the cows’ eyes.
Stress has traditionally been assessed by measuring heart rates, blood
cortisol levels and, more recently, blood haptaglobin levels. Looking
at eyes is simpler, inexpensive and fairly reliable.
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In the study, one group of cows was given an open box of fresh grass
and allowed to eat at will. Another group was given the same box,
except with a lid. The cows could see and smell the grass but they
couldn’t eat it.
Stress level was determined by looking at the whites of the cows’ eyes.
The whites of the frustrated group, even though they showed no other
signs of stress, were twice the size of the group that was
allowed to eat.
Researchers found that the greater the level of stress, the larger the
whites of the eyes.
One theory to explain this is that opening their eyes allows cows to
take in more visual information, which may help them deal with the
stressful situation.
Stress has many negative effects, but perhaps the most significant is
the way it decreases immune function, thus increasing susceptibility to
infection. It also affects fetuses.
In another study, ewes that were four weeks pregnant were subjected to
two stressful days by injecting them with cortisol, a hormone produced
naturally in the body that rises during periods of stress.
The ewes lambed normally four months later, but when the lambs were
five months old, they were found to have high blood pressure caused by
poor kidney development.
The researchers theorized that the ewes’ stress, which occurred during
the time that the fetus’ organs were developing, forced the kidney
cells to mature too fast. Though growth was accelerated, the kidneys
had less than two-thirds of a normal kidney’s filtering units.
The same effect is seen in people. Many studies have tied poor
nutrition to slow fetal growth and reduced birth weights. Babies born
to stressed mothers are at an increased risk of heart disease,
hypertension and adult-onset diabetes.
In people, maternal anxiety reduces blood flow to the fetus as much as
smoking during pregnancy. Noradrenaline, a hormone associated with
anxiety, is believed to constrict the arteries that feed the uterus.
When people and animals are stressed, either psychologically or through
such events as food scarcities, the fetus begins to starve for
nutrients. Its reaction is to divert blood and nutrients to the
developing brain, taking it away from other organs. This may cause
permanent changes to those organs.
In human terms, it means that pregnant women should eat well and stay
relaxed. In animals, it means good nutrition and minimal stress.
This research was reported in Nature magazine.
Jeff Grognet is a veterinarian and writer practising in Qualicum Beach,
B.C.
