Hanna Rich
Biology 1615
Tamara Neff- Tuesdays 1 pm
Impacts of Chronic Stress and Social Status on Various Physiological and Performance Measure in Pigs of
Different Breeds
M.A. Sutherland, S.R. Niekamp, S.L. Rodriguez-Zas, & J.L. Salak Johnson
I. Introduction
Pigs are often exposed to things that can be stressful to the animals throughout their lives,
which can in turn, create poor performance in the pigs. While there have been studies on the effects of
environmental stressors on pigs, there have not been many that also focus on the breed of the pig as a
variable. Crowding and high temperatures were the stressors used for two weeks. Blood draws taken at
different times during the experiment were used to analyze the results of the stress.
This experiment was done to see if differences in the breed and social status of commercial pigs
affected how the pigs reacted to stress on a physiological level. It has been shown that chronic stress
has a negative impact on the immune system, weakening it (apa.org).
The scientists who conducted the experiment hypothesized the pigs natural immune system
would be affected by its’ social status and breed. They also predicted that those two variables would
have an effect on performance (determined by body weight) and cortisol levels.
II. Materials and Methods
Three different breeds and two lines of pigs were used for this experiment; Landrace,
Meishan, and Yorkshire or lines A and B. The Landrace were the largest of the pig breeds, with
the Meishan being the smallest. All piglets were weaned at approximately the same age. An
equal amount of pigs were used for the control groups and for the stressed groups, separated
by sex. All pigs had access to water and good nutrition, 12 hours of light and 12 hours of
darkness, and were given time to adjust to the new environment.
All pigs had blood drawn on day 0 to determine normal levels of hormones and enzymes (also
known as baseline). The pigs that were chosen to be exposed to stressors were split into groups of
three, none of the three from the same litter, while the pigs in the control group were grouped with
littermates. The stressed pigs were placed in pens that were half the size of what’s recommended for
pigs of that size with a temperature 11 degrees higher than that of the control pigs. The pigs were then
video recorded for 24 hours to determine which of the pigs were dominant (DOM), intermediate (INT)
and submissive (SUB). DOM pigs were established by watching which of the 3 pigs won all of the fights
that the pigs engaged in, the INT was pig that won once or twice and the SUB was identified by its
reactions and stance with the other two pigs. Then, blood was drawn at day 7 and again at day 14 to
compare differences in the blood tests.
III. Results
Breed did not seem to play a role in the level changes seen in the pigs, seeing that variances
seen between the breeds existed from baseline. The Landrace were indeed larger than the other breeds,
but had been the largest from the beginning of the study. The pigs that were subjected to the constant
stressors were shown to have lower body weight than their control counter parts, indicating negatively
affected performance. Cortisol levels were shown to decrease in stressed pigs while the level of natural
killer cytotoxicity increased. In DOM pigs, the white blood cell count was higher than SUB pigs, indicating
they were better equipped to fight illness and disease.
IV. Discussion
The results of the data support the researcher hypothesis that when put under constant stress,
the pigs’ immune systems were negatively impacted. It also showed that a pig’s social standing does
have an effect on how its immune system responded to stressors in that SUB pigs regularly had lower
immune system responses than their DOM pen-mates. With the data available it would seem fairly
conclusive that social status is of great importance to a pigs immune responses, but more data needs to
be collected to make a definitive statement. Although researches believed that breed would be a factor
in the pigs’ immune responses, it was disproved that breed has an effect.
Works Cited
Journal of Animal Science “Impacts of Chronic Stress and Social Status on Various Physiological
and Performance Measure in Pigs of Different Breeds” M.A. Sutherland, S.R. Niekamp, S.L. RodriguezZas, & J.L. Salak Johnson. Mar 2006. Sept 17, 2013
American Psychology Association “Stress Weakens the Immune System” . np. nd. Web. Oct 12,
2013