Biomedical Engineering Reference
In-Depth Information
but were not affected by temperament. Epinephrine
concentrations peaked 1 h after LPS administra-
tion in calm bulls. Temperamental bulls did not
exhibit an epinephrine response to LPS challenge.
These data demonstrate that the temperament of
calves can modulate the physiological, behavioural
and endocrine responses of prepubertal Brahman
bulls to endotoxin challenge. Specifically, temper-
ament differentially affected the rectal tempera-
ture, sickness behaviour and epinephrine, but not
cortisol, responses to LPS challenge (Burdick
et al.
2011
). The study indicated that aggressive
behavioural or temperamental animals are able to
cope with challenges to immune system much
better than nonaggressive or calm animals.
5
Acute and Chronic Stressors
The stress response considered an all-or-nothing
biologic activity associated with the fight or flight
behaviour of Selye is not immunosuppressive.
Indeed, stress may elicit bidirectional effects on
immune response, acute stress may be immuno-
modulator or enhancer, whereas chronic stress
may be immunosuppressive (Carroll and Forsberg
2007
). Therefore, the immune response of an ani-
mal to stress depends on the type of stress encoun-
tered (i.e. acute vs. chronic). In acute stress,
hormones associated with priming the immune
system are released in a manner that prepares for
potentially countering invading pathogens and
subsequent infection. However, under prolonged
or chronic stress, the effect of stress hormones on
the immune system are no longer initial or pre-
paratory initiate events that are of suppressive
type, first at the cellular level and then, eventu-
ally, across the entire immune system.
Acute and chronic stressors affect the immune
responses that may vary. Chronic stress often
leads to suppression of the immune system, but
acute responses may or may not cause immuno-
suppression. In pigs, acute heat exposure and
transport stress had no effects on various immune
measures (McGlone et al.
1993
; Hicks et al.
1998
). But acute transportation stress reduces
chemiluminescence response of alveolar mac-
rophages and increases the ratio of CD4
+
to CD8
+
cells in cattle (Ishizaki et al.
2005
) . Acute cold
stress in pigs has been observed to cause an
increase in NK cytotoxicity (Hicks et al.
1998
) ,
whereas NK cytotoxicity had both positive and
negative response subjected to acute restraint
stress. Specifically, NK was increased during the
early phase (0-1 h) and decreased during the late
(3-4 h) phase of the stressor (Wrona et al.
2001
) .
Chronic stress may have differential effects on
the immune system. Chronic heat stress had
no effect on concanavalin-A or PHA-induced
lymphocyte proliferation (Bonnette et al.
1990
;
Morrow-Tesch et al.
1994
) .
A higher incidence of a variety of intramam-
mary infections during summer occurs (Waage
et al.
1998
; Cook et al.
2002
) , and a higher
4.3
Colostral Ig
Favourable environmental conditions are vital in
promoting calf health, minimising risk of dis-
eases and mortality, subsequently encouraging
growth rates. Moderate heat stress does not modify
significantly the protective value of colostrum, as
evaluated by determining the concentration of Ig
fractions. The total Ig concentrations in summer
colostrum do not differ or were higher than those
recorded during other seasons (Kruse
1970
;
Shearer et al.
1992
). Heat stress (THI >86 from
0900 to 2000 h and 76 from 2100 to 0800 h)
significantly reduced IgG and IgA in colostrum
of primiparous cows (Nardone et al.
1997
) . A
reduced passage of IgG from the bloodstream to
the udder result into an impairment of the immune
reactivity of the mammary gland plasmacytes
to synthesise IgA during heat stress in cows.
Extreme heat can negatively influence a cow's
ability to produce high quality colostrum and can
also negatively affect a calf's ability to absorb
IgG from colostrum (Stott
1980
) .
Summer heat stress is likely to mask the
immunosuppression taking place in periparturi-
ent dairy cows (Mallard et al.
1998
) . Heat stress
reduces thermogenic and immunosuppressant
hormones like growth hormone and glucocorti-
coids and may be related to the higher reactivity
of the immune system observed in cows exposed
to heat stress (Webster
1983
) .
