Biomedical Engineering Reference
In-Depth Information
the hot climate, and have been summarised in
publications (Habeeb et al.
1997
; Marai and
Habeeb
1998
) . Marai and Habeeb (
1998
) and
Marai et al. (
2008
) suggested the 'adaptability
index' as a parameter for estimating the heat
tolerance to the climatic conditions, using all the
traits, that is, thermal, water and/or nitrogen bal-
ances, as well as the physiological, productive or
reproductive traits of the animals under the con-
ditions which they have to live. The 'adaptability
index' equals 100− the average relative devia-
tions in the traits studied regardless of the minus
or plus signs. The relative deviation in each trait
was estimated as [the difference between the two
conditions in the values of the trait, i.e. the hot
and mild conditions (normal; control) divided by
the value of the trait in the mild conditions] × 100.
The selected animal for the hot region should
manifest the least changes in most of the para-
meters estimated (Marai et al.
2005,
2006,
2008
) .
Marai and his group have estimated the buffalo
adaptability index to the subtropical environment
of Egypt as 89.1%. The average value of the rela-
tive deviations as a function to the hot environ-
ment was 10.9%. Estimation of the adaptability
index using the data of El-Masry and Marai
(
1991
) showed nearly the same values in buf-
faloes (89.6% as adaptability index and the aver-
age relative deviations 10.4%). Adaptability for
Friesian cows was estimated as 82.9% in the sub-
tropical environment of Egypt on the same bases.
The estimated adaptability index can be used as a
simple and valid index for selection of high-
productive animals which maintain high milk or
meat production under hot climate conditions.
The gain in body weight may not be a reliable
indicator or mislead about heat adaptability
because the increase in body weight may also
occur due to increase either in body water or in
body protein and fat.
The adaptability of animal to heat needs to be
expressed in relation to production as indicated in
the recommendations of FAO/IAEA Panel (1974)
'Heat tolerance must be assessed in relation to
production and not only in relation to mainte-
nance of thermal balance'. The loss of body sol-
ids associated with a standard heat stimulus may
be an index. Kamal (
1993
) developed four heat
tolerance indices (HTI) related to hot summer
growth performance of young water buffalo
calves, depending on heat-induced changes in
some physiological and biochemical parameters.
These were the cortisol-HTI, glucose-HTI, evap-
orative water (EW)-HTI and nitrogen retention
(NR)-HTI. The cortisol-HTI and glucose-HTI
were applicable to young calves (6 months old).
Meanwhile, the EW-HTI and NR-HTI were
applicable to older calves (12 months old). Such
parameters can be used in screening heat toler-
ance in terms of growth or milk production under
hot climate. This is preferable to screening the
mature animals directly for productivity because
the latter is time consuming, as it takes 2 years
for the calves to reach their mature body weight
and 3 years at least to produce milk (Nessim
2004
). Such suggestions considered the main two
factors controlling productive performance under
heat stress are the genetic productive potentials for
growth and milk production and the heat tolerance
of the animal. The latter characteristic expresses
the animal's capability to attain, as much as, the
genetic maximum production under heat stress.
Other HTI parameters were suggested by other
workers (Rhoad
1944
; Lee and Phillips
1948
) .
Tunica dartos index (TDI) was developed to esti-
mate the ability of the bull and ram to tolerate
elevation of ambient temperature (El-Darawany
1999
; Marai et al.
2006
) .
10
Genetic Adaptations/Cellular
Changes During Heat Stress
The genetic adaptations developed in zebu cattle
in the process of its evolution are ascribed to the
acquisition of genes for thermotolerance. Zebu
breeds can regulate their body temperature under
vide range than
Bos Taurus
breeds of European
origin (McDowell et al.
1953
; Cartwright
1955
;
Allen et al.
1963
; Finch
1986
; Carvalho et al.
1995
; Hammond et al.
1996
) . Genetic differences
in their thermotolerance have been attributed to
the cellular functions (Malayer and Hansen
1990
;
Kamwanja et al.
1994
; Paula-Lopes et al.
2003
;
Hernández-Cerón et al.
2004
) . Thermal stress
triggers a complex programme of gene expres-
