EFFECT OF HOTLY SUMMER IN ASSIUT ON HEALTH STATUS, PRODUCTIVITY AND BEHAVIOR OF FRIESIAN DAIRY CATTLE AND THE EVALUATION OF TRADITIONAL

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1
Dept. of Animal Hygiene,
Fac. of Vet. Med., Assiut University.
EFFECT OF HOTLY SUMMER IN ASSIUT
ON HEALTH STATUS, PRODUCTIVITY
AND BEHAVIOR OF FRIESIAN DAIRY CATTLE
AND THE EVALUATION OF TRADITIONAL
By
S.A. KOTB; MADEHA H.A. DARWISH*
and M.A. ABDEL-RAHMAN*
*Dept. of Animal Behavior and Management.
Fac. of Vet. Med., Assiut University.
(Received at 2/10/2007)
تأثير الصيف الحار فى اسيوط على صحة وانتاج وسلوکيات أبقار الفريزيان
الحلوب وتقييم الطرق المعتادة للتخفيف
صابر عبد المتجلي قطب , مديحة حسنى احمد , معتز احمد عبد الرحمن
تم إجراء هذه الدراسة فى مزرعة للأبقار الحلوب داخل محافظة أسيوط خلال الفترة من يوليو
إلى اغسطس 7002 م على عدد 00 من الابقار الفريزيان والتي کانت تحلب بالنظام الالى
والتي کانت في نفس العمر والمرحلة الإنتاجية للحليب وذلک لمعرفة تأثير الظل والتبريد
المعتاد استخدامها على الکفاءة الإنتاجية للبن والنمطِ السلوکي في الماشية اِلحلابة. قسمت
الحيوانات الى ثلاث مجموعات کل منها يحتوي على عشرة حيوانات، سکنت المجموعة
الاولى داخل حظيرة بدون ظِ لِ والمجموعة الثانية سکنت في حظيرة مُظَل لة، بينما سکنت
المجموعة الثالثة داخل حظيرة دَعمتَ بالظِ لِ مع المرواح. تم قياس درجة حرارة الجو
والرطوبة وکذلک مؤشر الحرارة والرطوبة الدال على وجود اجهاد حراري وکذلک تم حساب
کمية الحليب المنتجة والنسبة المئوية لدهن اللبن وکمية العليقة التى يتناولها الحيوان في کل
مجموعة. کما تم قياس درجة حرارة جسم الحيوان ومعدل التنفس وبعض الانماط السلوکية
المرتبطة بالتغذية والإجهادِ . کما تم تقدير نسبة الجلوکوز وهرمون الکورتيزول في الدم وقد
أظهرت هذه الدراسة النتائج التالية: ان حيوانات انتاج اللبن داخل محافظة أسيوط تعيش تحت
ظروف بيئية صعبة وذلک من زيادة معامل الحرارة والرطوبة الدال على حدوث اجهاد
حراري وکان استخدام الظل مع المرواح داخل حظائر الحيوان له اثر في تخفيف حدة الاجهاد
الحراري للحيوانات نوعا ما وذلک من ظهور اثره على زيادة انتاجية الحليب ومعدل زيادة
تناول الحيوان للعليقة وکذلک من انخفاض درجة حرارة جسم الحيوان ومعدل التنفس. کذلک
لوحظ اثر ايجابي لاستخدام الظل او الظل مع المرواح داخل الحظائر على الانماط السلوکية
المرتبطة بالتغذية والإجهادِ للحيوانات. کما أشارت البيانات بأن، مستوي هرمون الکورتيزول
والجلوکوز کَان أعلى في مصل الأبقار التي أسکنت بدون ظل عن تلک التي أسکنت أما بالظل
فقط أَو بالظل والمرواح .
SUMMARY
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Thirty mid-lactation Friesian cows, 178 day post-partum were randomly
assigned to three equal groups (N= 10 per group). All animals were
blocked for age (6 year old), stage of milk yield and average body
weight. The experiment was carried out during the months of July and
August, 2007 in which the first group of the experimented- animal was
left in loose box without shade and expressed to heat stress while the
second group was left in shaded box (white galvanized metal roof, 4
meters above the ground and covered about 70% of the yard area).
However the later group left in a box supported with shade plus fans
(fans were installed regularly at height of 2.4 meters above the ground
and spaced 1.5 meters along the manger shed). Our study revealed that
provision of shade had no significant effect on temperature-humidity
index (THI) while providing shade and fans had significantly lowered
THI. At the same time the shade and fans had a significant effect on
daily milk production but shade alone had no significant effect on milk
yield. Milk yield was slightly increased with shade (insignificant) and
tended to be greater for shaded and cooled cows (significant) as compare
to non shaded animals. Also, this study indicated that, forage intake was
significantly lower for the experimented cows that housed without shade
than for those housed with shade and fans. Providing dairy cows with
access to shade or to shade and fans during summer season was effective
in reducing mean rectal temperature and respiratory rate. Moreover, this
study revealed some statistically significant differences in certain
behavioral patterns of cows that housed without shade under the
prevalent hot weather and those housed either under shade only or under
shade and fans (p<0.01). Moreover, leucocytic series of the
experimented cows was not significantly affected by any of the studied
housing conditions however cortisol and glucose levels were
significantly higher (p<0.01) in the serum of the experimented cows that
housed without shade than in those housed either with shade only or
with shade and fans.
Key words: Healthy status, reproductive behavior, dairy cattle hot sumner, and
behavior.
INTRODUCTION
When European breeds of farm animals are introduced to tropical
and subtropical countries, they are forced with many problems relating
to the hot climate, that induced conditions of heat stress which caused
by combination of environmental factors such as air temperature,
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relative humidity, solar radiation and wind speed. A vast array of
physiological, biochemical and behavioral changes were induced in such
animals.
Heat stress depresses feed intake and milk production in lactating
dairy cattle (Blackshaw and Blackshaw, 1994, Kadzere et al., 2002 and
west, 2003). When cow exposed to hot ambient temperatures, their
respiration rate and body temperature will increase (Spiers et al., 2004)
so, they adjust their behavior in an attempt to maintain thermal balance
(Bennett et al., 1985 and Blackshaw and Blackshaw 1994).
Relief from heat stress for dairy cattle can be achieved by
reducing the heat exchange from environment to the cow, and/or from
cow to environment. Heat stress abatement from dairy cattle begins with
providing shade (Her et al., 1988 and Kendall et al., 2006). Fisher et al.
(2002) reported that the use of shade was necessary for dairy cows when
ambient temperature exceeded 25ºC and was effective in reducing
animal temperature. Moreover, a good air exchange was helpful in
removing heat and reducing moisture, gas and pollutant levels. Forced
air movement improved convective heat transfer and speeds evaporation
of moisture from the skin (Dan McFarland, 2004). Several studies have
shown that cooled cows had lower rectal temperature and respiratory
rates than non-cooled ones (Armstrong et al., 1985; Armstrong et al.,
1988; Armstrong et al., 1993 and Chen et al., 1993).
The main objective of this study was to clarify the effect of hotly
summer in Assiut on health status, productivity and behavior of Friesian
dairy cattle and the evaluation of traditional ways to relief
MATERIALS and METHODS
1. Animals, feeding and management:
The study was carried out during the months of July and August,
2007. Animals were housed in a milking house system at the south east
of Assiut Governorate, Egypt. Each house consists of a closed house and
open yard with average space allowance of 25 m2/ head. Animals are
kept in open yards at daylight hours while they kept in the closed box
during night.
Thirty Friesian cows of the same age (6 year old) at their midlactation
period (178 day post-partum) were used in this investigation.
Cows were randomly assigned to three groups (N=10 per group) and
each group was housed in a separate house.
The study period in this investigation was 60 days preceded by a
14-day preliminary period. First group of animals was housed in a loose
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box without shade under the prevalent hot environmental weather while
the second group was housed in a box shaded with galvanized metal roof
of 4 meters height and covered about 70% of the yard area. However, the
third group was housed in a box supported with shade as previously
mentioned plus fans (fan was installed regularly at height of 2.4 meters
above the ground and spaced 1.5 meters along the manger shed with
power consumption of 60 ± 7 watt and speed equals 1150 ± 70 RPM ).
A fixed amount of commercial concentrate mixture was fed to
the animals in the milking parlour according to their average milk yield;
however, barseem was ad libitum offered to the experimented cows in
their loose boxes. Mineral salt rocks were hanged freely in front of the
animals. Cows were allowed free access to the water troughs which
placed on the ground of their boxes.
2. Climatic conditions:
Environmental temperature and relative humidity percentages
were determined by using wall mount – thermo-hygrometer, which was
hanged, above the level of the ground by about one meter inside the
examined building.
Temperature humidity index: (THI) was calculated according to
Ravagnolo et al. (2000) by equation of: THI= 1.8 x Ta- (1-RH) x (Ta-
14.3) +32. Where Ta is the average ambient temperature in oC and RH is
the average relative humidity as a fraction of unit.
3. Forage intake, health state and milk production:
1. To measure daily forage intake, the amounts of the feed offered and
refusals from each animal were recorded daily throughout the period of
the experiment. Refusals feed was removed and weighed daily just prior
to the morning feeding according to Little et al. (1979).
2. Animals were milked twice daily at 6.30 a.m and 5.00 p.m. The milk
yields for each animal were recorded daily and the average yield was
calculated daily as well as a weekly composite sample from the two
milking was analyzed for fat percentage using Gerber's methods (APHA,
1985).
3. Body temperature and respiratory rate were measured (according
Blood and Henderson, 1974) just prior to each milking. Rectal
temperature was measured by using medical thermometer and
respiratory rate was measured by counting the flank movements of the
individual cow and recorded as the number of inspirations per minute.
4. Behavioral patterns:-
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Behavior of the experimented animals was recorded according to
Marten and Bateson (1988) and Fordham et al. (1991) using direct
observation and scan sampling method where the observer can observe
the experimented cows without being seen by them. Behavior of the
experimented cows was recorded for 6 hours / day for 4 days / week for
two consecutive weeks for each experimental period as follows:-
- Two hours in the morning after supplying the animals with their
morning feeding (8:00 to 10:00 a.m.).
- Two hours in the afternoon (12:00 to 2:00 p.m.).
- Two hours in the evening after supplying the animals with their
evening feeding (5:00 to 7:00 p.m.).
Recorded behavior of the experimented cows was analyzed
according to Marten and Bateson (1988); Abdel-Rahman (1999) and
Kendall et al. (2006) as follows:-
1. Eating time / cow / recorded hour: - where the average time that each
cow was spent on eating during each recorded hour was calculated.
2. Number of eating bouts / cow / recorded hour: - where the average
number of eating bouts that each cow did during each recorded hour was
calculated. Eating bout is defined as eating activity which starts by the
time that the animal begin to move its jaw to eat and ends when it stop
chewing and swallowing the very last bolus. According to the previously
mentioned authors, eating bouts was not considered ended if they
returned to eat again within one minute.
3. Number of drinking bouts / cow / recorded hour: - where the average
number of drinking bouts that each cow did during each recorded hour
was calculated. Drinking bout is defined as drinking activity which starts
by the time that the animal dips its mouth into the water surface and
ended by raising of its head.
4. Time spent on water trough / cow / bout.
5. Standing time without eating or drinking activities /cow / recorded
hour: - where the average time that each cow spent on standing without
eating or drinking activities during each recorded hour was calculated.
6. Lying time / cow / recorded hour: - where the average time that each
cow spent on lying down and resting during each recorded hour was
calculated.
7. Behaviors of stress and restlessness: - where some behavioral patterns
of stress were recorded as follows: -
Bellowing:-
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Bellowing was defined as a loud vocalization emitted by stressed
cattle. Repeated vocalization by the same cow was considered as one act.
Pawing:-
Pawing was defined as rubbing the floor vigorously with the
claws of the hind limbs of stressed cattle.
Stamping or sniffing the ground.
Lip licking:-
It is another indicator of stress that defined as repeated and rapid
licking of the upper lip (muzzle).
5. Blood parameters:-
During the last two days of each study period, three blood
samples, 5 ml each were drawn from the jugular vein of each animal of
randomly selected five cows. The first one was drawn into glass test
tubes contain EDTA for leucocytic count according to Franke and
Reitman (1963). The second blood sample was drawn into centrifuge
tubes and centrifuged for 30 minutes at 3000 r.p.m and the obtained sera
were assayed within three hours for their glucose concentration
according to Tinder (1969). The third blood sample was drawn into
centrifuge tubes and centrifuged for 30 minutes at 3000 r.p.m and the
obtained sera were freezed at –80 ºC and kept for further analysis to
determine their cortisol level using TDx FLx system according to
Dandliker and Sassure (1973).
6. Statistical analysis:-
Statistical analysis of the collected data were carried out
according to procedures of completely random design, SAS (1995)
RESULTS
Table 1: Effect of shade and cooling on average prevailing
environmental condition.
Housing condition
Parameters
Without shade With Shade With Shade
and Fans
Mean air
Temperature (ºC)
35.87±0.75a 35.37±0.62a 34.25±0.68a
Mean relative
Humidity (%)
43.00±2.36a 40.75±1.75a 35.50±1.47b
Mean THI 84.27±1.48a 83.18±0.54a 80.78±0.90b
Figures in the same raw with different superscripts differs significantly (p<0.01).
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Table 2: Effect of shade and cooling on voluntary forage intake and
average milk production.
Housing condition
Parameters
Without shade With Shade With Shade
and Fans
Average forage
Intake (Kg/head/day)
9.23±1.05a 10.65±0.98a 13.63±0.78b
Mean milk yield
(Kg/head/day)
7.4±0.76a 8.15±0.62a 10.14±0.33b
Mean milk fat% 3.33±0.85a 3.46±0.09a 3.48±0.76a
Figures in the same raw with different superscripts differs significantly (p<0.01).
Table 3: Effect of shading and cooling on physiological parameters of
the animals
Housing condition
Parameters
Without shade With Shade With Shade
and Fans
Rectal temperature (ºC) 39.8±0.2a 38.9±0.1a 38.6±0.1b
Respiratory rate (Insp./min) 41±2a 31±1a 28±1b
Figures in the same raw with different superscripts differs significantly (p<0.01).
Table 4: Behavioral patterns of the animals under different conditions.
Housing condition
Behavior
Without shade With shade
With shade
and Fans
Eating time
(min. / hour)
13±2 a 18±1 a 24±1 b
Eating bouts
(No. / hour)
3±1 a 4±1 a 7±1 b
Drinking bouts
(No. / hour)
6±1 a 3±1 b 3±1 b
Drinking time
(Sec. / bout)
14±3 a 12±1 a 13±1 a
Standing without activities
(min. / hour)
33±4 a 18±2 b 11±2 b
Lying down
(min. / hour)
12±2 a 23±1 b 24±1 b
Bellowing
(% of animals)
40 a 0 b 0 b
Pawing
(% of animals)
0 a 0 a 0 a
Stamping or sniffing
(% of animals)
40 a 10 b 10 b
Lip licking
(% of animals)
60 a 10 b 10 b
Figures in the same raw with different superscripts differs significantly (p<0.01).
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Table 5: Differential leucocytic count (10 3 / μl).
Housing condition
Item
Without shade With shade With shade and Fans
Total WBCs 12.62±0.12 12.34±0.12 12.42±0.12
Neutrophils 7.34±0.10 7.26±0.10 7.24±0.10
Lymphocytes 3.41±0.10 3.32±0.10 3.36±0.10
Monocytes 1.21±0.04 1.17±0.04 1.18±0.04
Eosinophils 0.47±0.03 0.43±0.03 0.45±0.03
Basophils 0.190±0.01 0.160±0.01 0.190±0.01
Table 6: Serum cortisol (μg / L) and glucose (Mmol / L) concentrations.
Housing condition
Item
Without shade With shade
With shade
and Fans
Cortisol 1.22±0.02 a 0.87±0.02 b 0.82±0.02 b
Glucose 7.31±0.10 a 5.62±0.20 b 5.71±0.20 b
Figures in the same raw with different superscripts differs significant (p<0.01).
DISCUSSION
1. Effectiveness of shade and cooling:
Table (1) showed that the mean environmental air temperature
(ºC), relative humidity (%) and calculated temperature-humidity index
(THI) during the different experimental conditions were 35.87, 43.00
and 84.27 during housing without provision of shade, 35.37, 40.75and
83.13 during housing under shade, while it was 34.25, 35.5 and 80.78
during housing under shade and fans, respectively. The previously
mentioned data, showed that temperature-humidity index was higher
than temperature -humidity index above critical thresholds accounted for
heat stress (72) as stated by Armstrong et al. (1988) during different
housing condition, a finding which indicating the exposure of cows to
heat stress during the summer season. Also, it could be noticed that
provision of shade had no significant effect on THI while providing
shade with fans had significantly lowered THI (P<0.01). This result may
be attributed to the fact that provision of shade only protected the animal
from direct solar radiation and not reduces prevailing temperature
(Armstrong et al., 88 and Kendall et al., 2006).
2. Forage intake and milk production:
The data represented in Table (2) illustrated that, forage intake
for cows that housed without shade was 9.23 kg/head/day while it was
10.65 kg/head/day for cows that housed with shade only and 13.63±0.78
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kg/head/day for cows that housed with shade and fans. These data
indicated that, forage intake was significantly (p<0.01) lower for the
experimented cows that housed either with or without shade as
compared to those housed with shade and fans.
The reduction in voluntary forage intake and the subsequent
declines in milk production are direct responses to heat stress in lactating
dairy cows (Beede and Collier, 1986). The adverse effect on milk yield
was most likely mediated through a reduction in forage intake. Beede
and Collier (1986) reported that, if cows are fed diets that allow sorting
during high environmental temperatures, they selectively will decrease
forage intake relative to concentrates in an attempt to reduce body core
temperature through reduced heat production. The gross efficiency of
conversion of feed to milk was lower for heat stressed cows. This
suggested that an adaptive mechanism must have occurred in the heat
stressed cows, resulting in higher maintenance requirements and lower
efficiency of energy use for milk production. This, combined with the
decrease in forage intake, would explain the decreased milk yield for
these cows.
Also, the data represented in Table (2), showed the effect of
shade as well as shade and fans on the milk yield and milk fat%. These
data indicated that the shade plus fans had a significant effect (p<0.01)
on daily milk production, however housing under shade or shade plus
fans had no significant effect on milk fat %. Milk yield was significantly
increased (p<0.01) by shade and cooled cows (10.14 kg/head/day) as
compare to shade (8.15 kg/head/day) or non shaded animals (7.4
kg/head/day). However, the milk yield was relatively increases when
cows were shaded and cooled in comparison cows in shade only. This
finding was agreed with Tarazon- Herrera et al. (1999) and Kendall
et al. (2006). In addition, our study showed a non significant effect of
shade and cooling on milk fat% and this result coincided with Tarazon-
Herrera et al. (1999) who reported that the milk fat% not affected by
using shade or cooling. Typically, milk production declines as THI
increases (Spiers et al., 2004) and this influence is magnified by
consecutive hot days (Davison et al., 1988). While shade and cooling
does provide some cumulative production benefit where the cows may
have a sufficient cooling period to consumed feed to prevent any further
decline in milk production (Igno et al., 1992).
3. Physiological paramaters:
Providing dairy cows with access to shade or to shade and fans
during summer season was effective in reducing mean rectal temperature
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10
and respiratory rate from 39.8°C and 41 No./min. in non-shaded cows to
38.9°C and 31 No./min. in shaded group and 38.6°C and 28 No./min. in
shaded and cooled group, respectively. Several studies such as Roman
ponce et al. (1977); Davison et al. (1988) and Muller et al. (1994b)
have also found that average body temperature was lower in shaded
lactating cows than in cows with no shade. Also, Roman ponce et al.
(1977) and Davison et al. (1988) found a positive reducing effect in
respiratory rate in shaded cows than non shaded one.
The present findings concerning the decrease of rectal
temperature and respiratory rate in cooled and shaded cows was agreed
with that recorded by Armstrong et al. (1985); Armstrong et al. (1988);
Armstrong et al. (1993) and Chen et al. (1993). Rectal temperature is a
sensitive indicator of thermal balance and may be used to assess the
negative effects of hot environment on growth, lactation and
reproduction of dairy cows (Johnson, 1985 and West, 1993). It has been
shown that a rise of 1 ºC or less in rectal temperature is enough to reduce
intake and production in dairy cattle (Johnson et al., 1963).such decrease
in rectal temperature and respiratory rate indicates a much stronger
response to the environment for shaded and cooled cows. These results
coincided with Muller et al. (1994b), who found that cows without
access to shade had a higher rectal temperature than shaded cows and
that non-shaded cows were more susceptible to increase in ambient
temperature.
4. Behavioral observations:-
A comparative evaluation of the data represented in Table (4)
revealed statistically significant differences in some behavioral aspects
of cows that housed without shade under the prevalent hot weather and
those housed, either under shade only or under shade and fans (p<0.01).
The behavioral data represented in Table (4) illustrated that,
eating time (min./hour), eating bouts (No./hour), drinking bouts
(No./hour), drinking time (sec./bout), standing time without activities
(min./hour) and lying time (min./hour) for cows that housed without
shade were 13, 3, 6, 14, 33 and 12 respectively while it were 18, 4, 3, 12,
18, 23 for cows that housed with shade only and 24, 7, 3, 13, 11, 24 for
cows that housed with shade and fans, respectively. These data indicated
that, both eating time, eating bouts and lying time were significantly
lower for the experimented cows that housed either without shade or
with shade only than for those housed with shade and fans. However,
drinking bouts and the time that the cows spent standing without
activities were significantly higher for the experimented cows that
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11
housed without shade than for those housed either with shade only or
with shade and fans, which were insignificantly different. Moreover,
these data indicated that the time that the cows spent drinking was
insignificantly affected by any of the studied housing conditions.
With regard to behavioral aspects of stress and restlessness, the
data represented in Table (4) illustrated that, the incidences of bellowing,
pawing, stamping or sniffing the ground and lip licking among cows that
housed without shade were 40, 0, 40 and 60 %, respectively while it
were 0, 0, 10, 10 % for cows that housed with shade only and were 0, 0,
10, 10 % for cows that housed with shade and fans, respectively. These
data indicated that, the incidences of bellowing, stamping or sniffing the
ground and lip licking were significantly (p<0.01) higher among the
experimented cows that housed without shade than those housed either
with shade only or with shade and fans, which were insignificantly
different. However, the incidence of pawing the ground was zero for all.
The finding of this study agreed with Parker (1980); Sainsbury
(1988); Pfau et al. (1992) and Kendall et al. (2006) who indicated that,
housing of cows without shade under the prevalent hot weather reflected
with a prominent disturbances on their behavioral patterns, specially
those mentioned before, and these disturbances can be assessed as signs
of stress and should be included in the practical management and
monitoring system of cows.
5. Blood parameters:-
The data represented in Table (5) showed the effect of the studied
housing conditions on the differential leucocytic count of the
experimented cows. These data showed that, the counts (103 / μl) of total
WBCs, neutrophils, lymphocytes, monocytes, eosinophils and basophils
due to housing of the experimented cows without shade under the
prevalent hot weather were 12.62, 7.34, 3.41, 1.21, 0.47 and 0.190
respectively. However, it were 12.34, 7.26, 3.32, 1.17, 0.43, 0.160 and
12.42, 7.24, 3.36, 1.18, 0.45, 0.190 following housing the experimented
cows under shade only and shad with fans respectively. This result
indicated that, leucocytic series of the experimented cows was not
significantly affected by any of the studied housing conditions.
At the same time, the data illustrated in Table (6) showed the
effect of these studied conditions on the serum levels of cortisol and
glucose of the experimented cows. Serum cortisol and glucose levels
were 1.22, 0.87, 0.82 μg / L and 7.31, 5.62, 5.71 Mmol / L following
housing of the experimented cows under the prevalent hot weather
without shade, with shade, with shade & fans respectively.
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12
These data indicated that, both of cortisol and glucose levels
were significantly higher (p<0.01) in the serum of the experimented
cows that housed without shade than in the serum of those housed either
with shade only or with shade and fans, which were insignificantly
different. The significant increase in the blood cortisol level of the
experimented cows that housed without shade indicating an occurrence
of stress and may be related to an outpouring of ACTH which intern
stimulates the adrenal cortex to increase its secretion of glucocorticoids
including cortisol (McDonald, 1969; Burchfield et al., 1980 and
Stephens, 1981). However, the increase in blood glucose level of the
same cows may be related to the fact that glucocorticoids, including
cortisol, act on the hepatocytes which induced to produce gluconeogenic
enzymes which in turn increase the rate of gluconeogenesis and enhance
the conversion of protein to glucose. Moreover, cortisol causes a
moderate reduction in the rate of glucose utilization by the body cells,
which leads to a rise in blood glucose level (Guyton and Hall, 1996).
CONCLUSION
In conclusion, housing of dairy cows without shade was found to
have an adverse effect on health, productivity and behavior. The data
suggested that shade and fans were not sufficient to completely eliminate
heat stress in cows because maxima for THI measured under the shade
and fans remained high enough to decrease milk yield. The significant
decrease in respiratory rate and rectal temperature of cows showed a
partial alleviation of heat stress resulted from shade and fan, the effect of
which was confirmed by the increases milk production and reduced
losses.
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