Biomedical Engineering Reference
In-Depth Information
affected by hyperthermia. The ability to use
powerful new tools in genomics, proteomics
and metabolomics to evaluate genetic diffe-
rences between animals in their response to
thermal stress will yield important new infor-
mation in the next quarter-century and will
permit the selection of cattle for resistance to
thermal stress.
Improving milk production is, therefore, an
important tool for improving the quality of life
particularly for rural people in developing coun-
tries. The hot-dry environment is relatively less
harmful than hot-humid. In hot and humid cli-
mates, high ambient temperature and humidity
and high direct and indirect solar radiation, wind
speed and humidity are the main environmental
stressing factors that impose stress on livestock
species (Silanikove
2000
; Kadzere et al.
2002
) .
1
Introduction
2
Effect of Climatic Variables
on Milk Yield
Heat stress has adverse effects on milk produc-
tion and reproduction of dairy cattle (Kadzere
et al.
2002
; Hansen
2007
) . The problem of heat
stress is growing because increases in milk yield
result in greater metabolic heat production and
because of anticipated changes in the global cli-
mate (Hansen
2007
). A decline in milk yield of
lactating cows and buffaloes is observed during
hot-dry and hot-humid seasons due to high tem-
perature and humidity. High THI (temperature
humidity index) negatively impacts milk yield
that occurs due to increase in body temperature
(Upadhyay et al.
2009
) . Therefore, a major chal-
lenge for high-producing cow and buffaloes
under tropical environment is heat stress. It was
expected that regulation of body temperature
during hyperthermia would be decreased as milk
yield increased because of the metabolic heat
output associated with lactation. This was dem-
onstrated experimentally in dairy cows in Israel
(Berman et al.
1985
) and theoretically using
mathematical models of heat balance in dairy
cows (Berman
2005
). Summer depression in fer-
tility in dairy cows was more pronounced for
cows with greater milk yield (Al-Katanani et al.
1999
). It was traditionally thought that milk syn-
thesis begins to decrease when the THI exceeds
72 (Armstrong
1994
), but with increasing milk
production, it has been observed that high-yielding
dairy cows reduce milk yield at a THI of
approximately 68 (Zimbelman et al.
2009
) . The
increasing concern with the thermal comfort of
dairy cows is justifiable not only for countries
occupying tropical zones but also for nations in
temperate zones in which high ambient tempera-
tures are becoming an issue (Nardone et al.
2010
) .
Climatic factors such as air temperature, solar
radiation, relative humidity, air flow and their
interactions often limit animal performance
(Sharma et al.
1983
) . Quantifying direct environ-
mental effects on milk production is difficult as
milk production is also strongly affected by other
non-environmental and environmental factors
such as nutritional and management (Fuquay
1981
) . Thatcher (
1974
) and Johnson (
1976
)
reported decline in the milk and fat production
due to direct effect of high temperature on the
synthetic and secretory activity in mammary
gland of cows (Silanikove
1992
) . McDowell et al.
(
1976
) also reported decline in milk production
by 15%, accompanied by a 35% decrease in the
efficiency of energy utilisation for productive
purposes in lactating Holstein cow at high tem-
perature on shifting them from an air temperature
of 18-30°C. Milk fat, solids-not-fat and milk pro-
tein percentage was also observed to decrease by
39.7, 18.9 and 16.9%, respectively. Johnson
(
1976
) also attributed 3-10% of the variance in
lactation milk production to climatic factors.
Differences in the physiological responses of
cattle to the form and duration of heat stress have
been reported, and differences have also been
noted in productive responses. Bianca (
1965
)
measured a 33% reduction in milk production by
different breeds of cows from temperate climates
exposed continuously to high (35°C) ambient
temperatures. However, cows maintained under
similar temperatures during the day but at <25°C
at night did not decrease milk production
