Download Physiological indices in buffaloes exposed to sun

Archiva Zootechnica vol. 10, 2007
127
Physiological indices in buffaloes exposed to sun
D. Gudev1, S. Popova-Ralcheva1, P. Moneva1, Y.Aleksiev2, Tz.
Peeva3, P. Penchev3, I.Ilieva3
1
Institute of Animal Science – 2232 Kostinbrod, Bulgaria
Institute of Mountainous Animal Breeding and Agriculture – 5600 Troyan,
Bulgaria
3
Agricultural Institute – 9700 Shumen, Bulgaria
2
ABSTRACT
Ten lactating buffaloes were kept in a barn or exposed to direct solar
radiation (air temperature 30.2 0C) for 12 h. Rectal temperature (RT) and
respiratory rate (RR) were measured at 8 h, 11 h, 15 h and 20 h. Both RT and
RR increased significantly at temperature – humidity index (THI) - 77.83,
showing that the lactating buffaloes are sensitive to heat stress and are not able
to maintain their core temperature within the thermoneutral zone. The same THI
had no significant effect on rectal temperature elevation when the buffaloes
were kept in barn. The obvious heat stress, assessed by the rate of RT and RR
elevations, was not accompanied with an enhancement of plasma cortisol level.
The unchanged plasma cortisol level in the buffaloes under heat is interpreted
within the context of the hormonal integration and the modulating effect of
hypothalamic-pituitary-adrenal axis on the other endocrine glands involved in
the thermal homeostasis maintenance. These data demonstrate that lactating
buffaloes need protection against the direct solar radiation.
Key words: lactating buffaloes, stress, thermoregulation, cortisol.
INTRODUCTION
Increasing air temperature above critical threshold is related with reduced
feed intake (Holter et al.1996; Holter et al., 1997) decreased activity, milk yield
(Umphrey et al., 2001) and a deleterious effect on the physiologic status (West
2003) of farm animals. The effect of heat stress on the physiological status of
lactating buffaloes is relatively less studied in comparison with that in lactating
cows.
It has been found that the upper limit of Temperature Humidity index (THI)
at which cattle may maintain stable body temperature is between 72 (Ravagnolo
et al., 2000) and 76 (Igono et al., 1992) depending on the breed and air velocity.
Rectal temperature (RT) and skin temperature have been reported to
fluctuate much more in buffaloes than in tropical cattle under increased ambient
temperature (Koga et al., 2004). Consequently the aim of the present study was
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to evaluate the effect of direct solar radiation on buffalo heat-tolerance under
the summer temperatures, typical for Bulgaria
MATERIAL AND METHODS
The experiment was carried out at the experimental buffalo farm of the
Agricultural Institute-Shumen (North-Eastern Bulgaria). Air temperature in this
region usually surpasses 30oC in July and August and could reach up to 37oC.
The experiment comprised 10 lactating buffaloes (Bulgarian Murrah
breed), which were kept in shade or exposed to direct solar radiation during
sunny days with ambient temperature not less than 300C. When in shade the
buffaloes were housed in a 4 rows barn during the experiment. When in sun the
buffaloes were kept on a concrete ground that could be lit up by the sun
throughout the day. The animals were tied for the mangers and were fed on a
diet formulated to meet established nutrient requirements. During the
experimental period the buffaloes were fed once daily at 4 a.m., before the
morning milking. The animals were watered during the intervals between the
measurements by the use of pails. All measurement were conducted on 2 days (
1 in shade and 1 in sun.
Rectal temperature (RT) and respiratory rate (RR) were measured at 8 h, 11
h, 15 h, and 20 h. Rectal temperature was registered with electronic
thermometer and RR by counting flank movements. Air temperature was
measured by a mercury thermometer; wind velocity - by catathermometer and
relative humidity - by a psychrometer (measuring the difference between the
dry and wet bulb temperature). The abiotic factors were registered immediately
after each measurement of the physiological parameters.
Temperature humidity index (THI) was calculated as follows:
THI=(0.8 X ambient temperature + [(% relative humidity/100) X ambient
temperature – 14.4)] + 46.4, (Tom, 1959).
The intensity of heat load was calculated by the formula of Benezra (1954)
as follows:
Heat load (HL) - T/38.45 + RR/18.40
Where T- maximum RT during heat load
RR- maximum RR during heat load
38.45- average RT at thermoneutrality
18.4- average RR at thermoneutrality
The average values of RT and RR measured at 8 a.m. were used as
thermoneutral values.
Blood samples were taken by venipuncture at 8 a.m. and 2 p.m.
Plasma cortisol levels were measured by the radioimmunoassay (Kanchev
et al. 1976).
The results of one factor statistical analysis are expressed as means ±
S.E.M. and were analyzed by Student t-test. When the results were statistically
processed by the use of two factors analysis the difference was less than 3%.
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Rectal temperature 0C
RESULTS AND DISCUSSION
Rectal temperature values were significantly higher (P<0.05) at 3 p.m.
during the exposure to direct solar radiation compared to the RT values
measured in the barn (Fig. 1), despite the similar values of THI in the open air
and in the barn (Fig. 2). Furthermore the greater increase of RT in the buffaloes
kept in sun occurred on the background of 2.0 times higher air velocity
compared to the morning value (Fig. 3), and it is known that external wind
breaks up the layer of air retained by the fur and increases convective heat
transfer.
39
38.8
38.6
38.4
38.2
38
37.8
Exposed
to sun
Kept in a
barn
8
11
15
20
Time - hours
Temperature - humidity
index
Fig. 1. Diurnal dynamics of rectal temperature (t0C) in lactating buffalos exposed
to sun or kept in barn during hot summer days
100
Exposed to
sun
Kept in a
barn
80
60
40
20
0
8
11
15
20
Time - hours
Fig. 2. Daily dynamics of temperature-humidity index in open air and in barn
Rectal temperature values of the buffaloes kept in the barn were not
significantly higher at 3 p.m. compared to those at 8 a.m. and 11 a.m. (Fig. 1).
However, RR increased significantly at 11 a.m. and 3 p.m. compared to RR at 8
a.m. (Fig. 4). Therefore when kept in the barn the buffaloes maintained their RT
within the thermoneutral zone at the expense of higher RR. According to Bianca
(1976) the zone of thermal indifference can be determined by using as its upper
limit the environmental temperature at which evaporation from the respiratory
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Air velocity - m/sec
tract begins to rise (critical temperature for evaporation). Panting is known to
involve greater expenditure of energy than sweating, thus increasing
endogenous heat production (Robertshaw and Taylor, 1969). Regretfully we do
not know the level of RR in buffaloes at which panting sharply increases the
loss of CO2 via pulmonary ventilation, thus reducing blood concentration of
carbonic acid and resulting in respiratory alkalosis (West, 2003).
2,5
Exposed
to sun
Kept in a
barn
2
1,5
1
0,5
0
8
11
15
20
Time hours
Respiratory rate resp/min
Fig. 3. Daily dynamics of air velocity (m/sec) in open air and in barn
40
Exposed
to sun
Kept in a
barn
30
20
10
0
8
11
15
20
Time - hours
Fig. 4. Diurnal dynamics of respiratory rate (resp/min) in lactating buffalos
exposed to sun or kept in barn during hot summer days
The exposure to direct solar radiation resulted in significant enhancement
of both RT (P<0.05) and RR (P<0.001) at 3 p.m. (Fig. 1 and Fig. 4), showing
that the animals were not able to maintain RT within thermoneutral zone in
spite of the increased RR and air velocity (Fig. 3) at that time. Our data are
consistent with the results reported by Koga et al., (2004) who found that rectal
temperature fluctuates much more in buffaloes than in tropical cattle with
changes in ambient temperature. The greater sensitivity of the buffaloes to hot
conditions especially when exposed to direct solar radiation could be due to the
dark body, lesser density of sweat glands and the thick epidermis (Sastry, 1983)
which reduce the capacity of cutaneous evaporation. Furthermore it has been
established that water excretion rate through urine in buffaloes is higher than in
cattle and that buffaloes have a grater dependence on external water because of
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Cortisol - ng/ml
the evolutionary adaptation of buffaloes to wet environments (Koga et al.,2004).
It is known that radiation in the visible part of the spectrum (300 to 700 nm ) is
absorbed at or near the outer surface of the black fur and its penetration at
greater depths depends on hair density. The calculated HL index by Benezra`s
formula was 2.77. Our data indicate that lactating buffaloes raised in Bulgaria
should be protected against direct solar radiation during hot summer months,
when ambient temperature is above 30 0 C (THI – 77.8).
3.5
3
2.5
2
1.5
1
0.5
0
8h
14 h
Fig. 5. Plasma cortisol levels in lactating buffaloes exposed to sun
Plasma cortisol level at 2 p.m. tended to be lower than that at 8 a.m. inspite
of the increased RT and RR at 2 p.m. showing that heat load on the buffaloes
was high enough to cause stress. (Fig.5). These results are consistent with those
in our previous experiment with cows subjected to transport stress, followed by
exposure to heat stress (35oC, relative humidity-50%) in climatic laboratory for
7 h (Gudev et al., 2004). Plasma cortisol increased sharply following the
placement of the cows in the climatic laboratory and declined 2 h later to levels
that were within the normal range in spite of the fact that the cows were under
severe heat stress as evidenced by the enhanced values of RT and RR.
The discrepancy between the unchanged levels of the classical stressindicator (cortisol) observed in both experiments against the background of
increased head load, indicated by the enhanced RR and RT , could be explained
with the specific role of hypothalamic-pituitary-adrenal axis in acclimatory
responses to thermal stress (Collier et al.,1982; Beede et al.,1986).
Corticotrophin-releasing hormone is known to stimulate somatostatin
release from the hypothalamus which in its turn inhibits growth hormone and
thyroid stimulating hormone secretion from the pituitary (Riedel et al., 1998).
The unchanged plasma cortisol levels in the buffaloes exposed to direct
solar radiation at 2 p.m. suggest that corticotrophin-releasing hormone secretion
was not changed either. Therefore, neither somatostatin secretion nor growth
hormone or thyroid–stimulating hormone were expected to be influenced by
corticotrophin–releasing hormone at 2 p. m. in the exposed to direct solar
radiation buffaloes. This putative hormonal pattern will help the animals to
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dissipate the heat, obtained from the environment, since cortisol is calorigenic
hormone (Yousef and Johnson, 1967) and its elevation will produce further
increase of endogenous heat production, thus aggravating body capacity to
dissipate the accumulated endogenous and environmental heat. Besides, growth
hormone stimulates sweating rate (Manalu et al., 1991), but at the same time it
increases heat production (Yousef, 1985). Furtermore, growth hormone
enhances conversion of T4 to T3 thereby increasing metabolic rate (Wolthers et
al., 1996). Consequently, the expected lack of change in plasma growth
hormone level at 2 p.m. could be considered as a compromise between its heat
stimulating and heat dissipating effect.
Taken together, our data suggest that the unchanged activity of
hypothalamic pituitary adrenal axis in the buffaloes under heat should be
viewed not only within the thermoregulatory implication of this axis, but also
within its integration with the other endocrine glands that take part in the
maintenance of body temperature homeostasis.
CONCLUSIONS
Exposure of lactating buffaloes to direct solar radiation (THI-77.83) caused
significant elevation of RR and RT showing that heat load was greater than the
body capacity to dissipate the heat. The same value of THI did not induce
significant changes in RT when the buffaloes were kept in barn, although the
maintenance of RT within the thermoneutral zone was achieved at the expense
of higher RR.
Plasma cortisol level was not significantly influenced by the exposure to
heat stress.
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