Biomedical Engineering Reference
In-Depth Information
of stress. To better understand how an environ-
mental heat load influences the set points of seve-
ral metabolic pathways within skeletal muscle,
Rhoads et al. (
2008
) examined heat stress effects
on skeletal muscle of beef cattle adaptation to
chronic heat stress using microarray analysis.
Skeletal muscle (semimembranosus) biopsies
were obtained during thermal neutral conditions
and again after exposure to heat stress. Data inter-
rogation by pathway analysis identified dramatic
changes in the skeletal muscle transcriptional
profile revealing that during heat stress, bovine
skeletal muscle may experience mitochondrial
dysfunction leading to impaired cellular energy
status. This may have broad implications for the
reduced growth, decreased milk production and
heat intolerance observed in ruminants during
heat stress especially if skeletal muscle is not
able to make necessary contributions to whole-
body energy homeostasis. Taken together, the
microarray data demonstrate that bovine cells
and tissues undergo changes in cellular beha-
viour, which may be important for individual
tissue function, whole-body metabolism and
overall physiological acclimation to heat stress.
thermoneutral zone forces an animal to utilise
compensatory mechanism to maintain its body
temperature within normal limits. Management,
housing, diet and climate affect the energy require-
ments of the animal. Cattle from zebu breeds are
better able to regulate their body temperature in
response to heat stress than are cattle of
B
.
taurus
breeds of European origin. Among the genetic
adaptations that have developed in zebu cattle dur-
ing its evolution have been the acquisition of genes
for thermotolerance and disease resistance. Thus,
an alternative scheme to crossbreeding for utilis-
ing the zebu genotype for livestock production in
hot climates is to incorporate those zebu genes that
confer thermotolerance into European breeds
while avoiding undesirable genes. Heat stress
reduces milk production in cows with high genetic
merit for milk production. Strategies to alleviate
metabolic and environmental heat loads in early
lactation need to be developed. Milk production
per cow has increased over threefold in response to
advances in animal nutrition, in technology and in
biotechnology as well as genetic progress for milk
production. Using these facts as a basis, it is appar-
ent that genetic selection and other variables
enhancing milk production may have resulted in
adjustments in factors important to lactation and
nutritional physiology of the dairy cow. One such
factor, important especially in hot environments, is
the thermoregulatory capabilities and the physio-
logical effects of heat stress on high-producing
cows. There is a need to further define the physio-
logical and cellular basis for thermotolerance in
zebu cattle and buffaloes that associate with their
disease resistance. The understanding will help
targeting identified genes responsible for better
adaptation and to exploit the zebu genome for
improving their production under tropical climate
conditions under limited resources.
13
Conclusions
High ambient temperature is a major constraint on
animal productivity in tropical climates since it
evokes series of drastic changes in the animal's
physiological functions that include depression in
feed intake efficiency and utilisation; disturbances
in metabolism of water, protein, energy and min-
eral balances, enzymatic reactions, hormonal
secretions and blood metabolites. Such changes
result in impairment of production and reproduc-
tion performance. The effect of heat stress is
aggravated when it is accompanied by high ambi-
ent humidity. Susceptibility to heat stress depends
on many factors, including adaptation, housing
and management. Determining nutrient require-
ments for animals exposed to different climates
and effective ambient temperature is a significant
challenge that requires consideration of many
factors affecting animal's ability to maintain a
normal temperature. Heat and cold outside the
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