Biomedical Engineering Reference
In-Depth Information
Fig. 1
Thermoneutral zone (Kadzere et al.
2001
)
Igono et al. (
1992
) measured the highest milk
production in Holstein cows under a desert
environment maintained at ambient temperatures
below 21°C throughout the day. McArthur and
Clark (
1988
) indicated that the TNZ was related
to the heat and water balance of animal. The
farther an animal moves away from its preferred
body temperature, the productive processes are
likely to be affected more. McDowell et al. (
1976
)
also reported that even small increase in core
temperature has profound effects on tissue and
endocrine functions that, in turn, can negatively
affect animal fertility, growth, lactation and the
ability to work.
upon ambient thermal demand below the LCT
(Yousef
1985
). Below the LCT, animal metabo-
lism must increase to generate heat to maintain
core temperature. This can be accomplished
through increased energy intake. The general rule
of thumb is that energy intake must increase by
1% for each degree of cold below the LCT.
Non-evaporative heat loss declines as ambient
temperatures rise above the LCT making the
animals more dependent on peripheral vasodila-
tation and water evaporation to enhance heat loss
and to prevent a rise in body temperature.
2.2
Upper Critical Temperature (UCT)
2.1
Lower Critical Temperature (LCT)
The UCT is the air temperature at which the ani-
mal increases heat production as a consequence
of a rise in core temperature mainly due to an
inadequate evaporative heat loss (Yousef
1985
) .
Estimates of UCT are based on studies on dairy
cows exposed for short periods to constant
temperatures in climatic chambers (Kibler
1964
) .
The ambient temperature below which the rate of
heat production of an animal under resting state
increases to maintain body heat balance is the
lower critical temperature (LCT). This implies
that the rate of heat production is dependent
