Biomedical Engineering Reference
In-Depth Information
Table 2
Average thyroxine, triiodothyronine, insulin and cortisol levels in crossbred cows kept with and without mist
cooling
Hot-dry season
Hot-humid season
Without
cooling
With cooling
by mist and fan
Without
cooling
With cooling
by mist and fan
Hormone
D change
D change
Thyroxine (ng/ml)
45.79 ± 0.54
46.26 ± 0.47
+0.47
44.49 ± 0.51
46.21 ± 0.94
+1.72
Triiodothyronine (ng/ml)
1.52 ± 0.05
1.35 ± 0.04
−0.17
1.33 ± 0.33
1.35 ± 0.03
+0.02
9.08 ± 0.40
10.15 ± 0.30
+1.07
6.00 ± 0.29
8.86 ± 0.23
+2.26
Insulin ( m U/ml)
Cortisol (ng/ml)
4.17 ± 0.15
2.38 ± 0.07
−1.79
4.35 ± 0.25
2.83 ± 0.04
−1.52
Source: Aggarwal and Singh (
2009
)
Table 3
Average values of thyroxine, triiodothyronine, insulin and cortisol levels in showering and wallowing groups
during hot-dry and hot-
humid season
Hot-dry season
Hot-humid season
Buffaloes under
water showers
Buffaloes under
water showers
Parameter
Wallowing buffaloes
Wallowing buffaloes
Thyroxine
50.65 ± 0.50
52.57 ± 0.67
48.25 ± 0.54
50.57 ± 0.61
Triiodothyronine
1.97 ± 0.03
1.88 ± 0.03
1.83 ± 0.04
1.99 ± 0.03
Insulin
8.30 ± 0.26
10.86 ± 0.27
7.86 ± 0.33
9.62 ± 0.30
Cortisol
4.80 ± 0.14
2.60 ± 0.08
4.33 ± 0.16
2.64 ± 0.32
Source: Aggarwal and Singh (
2010
)
have a positive correlation to weight gain or tis-
sue production (Magdub et al.
1982
) . The plasma
T
4
and T
3
levels decreased under heat stress as
compared to thermoneutral conditions (Magdub
et al.
1982
) .
The response of T
4
and T
3
to heat stress is slow
and it takes several days to weeks for levels to
reach a new steady state (Silanikove
2000
) . A
decline in the plasma concentrations of T
4
from
2.2 to 1.16 ng/ml has been reported by Johnson
et al
.
(
1988
) whereas a reduced thyroid activity in
thermal acclimated cattle has been reported by
Gale (
1973
). This decline in thyroid hormones
along with decreased plasma GH level has a syn-
ergistic effect to reduce heat production (Yousef
and Johnson
1966b
) .
Thyroid hormones play an important role in
growth regulation and are essential for mainte-
nance of the basal metabolic rate (Carlson
1969
) .
Thyroxine (T
4
) and triiodothyronine (T
3
) are bio-
logically active, and T
3
is several times more
active than T
4
. Seasonal rhythm occurs in the
level of some of these hormones. T
3
level was
found to be at maximum in winter, decreased in
spring and continued to decline reaching the
lowest value in summer in both buffaloes and
Friesians (Kamal and Ibrahim
1969
) . T
3
was
found to take at least 72 h to reach its minimum
level after heat exposure (Kamal and Ibrahim
1969
) . The decline in T
3
in the heat-stressed buf-
faloes may be responsible for the decline in milk
components during the hot July month in Egypt
(Habeeb et al.
2000
) and the decline (
P
< 0.01) in
daily body weight gain with elevated temperature
(Habeeb et al.
2007
) . The relatively high total
solid (fat, protein and lactose) percentages
observed during February can be ascribed to the
favourable conditions of the mild climate and
abundance of green fodder in winter (Habeeb
et al.
2000
). In a comparative study in buffaloes
kept under water showers and allowed to wallow-
ing, it was found that wallowing buffaloes had
higher levels of T
4
(Aggarwal and Singh
2010
;
Table
3
) during hot-dry and hot-humid seasons.
In young and old buffalo calves, acute heat
exposure (33-43°C, 40-60 RH%) was observed
to decrease plasma T
3
and T
4
levels (Nessim
2004
) . Plasma concentration of T
3
was found to
decrease significantly when ambient temperature
rose from 24 to 38°C in the climatic chamber in
