State of Acid-base Balance in Dehydrated Camels (Camelus dromedarius)
There is a lack of information pertaining to the normal levels of acid-base parameters and the effects of dehydration on the acid-base balance in camels. The effect of water deprivation on acid-base balance was studied using five (2-years old) male dromedary camels. The camels were deprived of water for 7 days. Respiratory rate and blood gases were determined before the commencement and at the end of water deprivation period and during the first 48 h post rehydration. Blood pH did not differ significantly (p = 0.14) due to water deprivation in camels. However, respiratory rate was significantly (p = 0.001) elevated, while blood partial pressure of CO2 (pCO2), total CO2 (tCO2) and bicarbonate (HCO3-) were significantly (p<0.1) reduced in water deprived camels. This study demonstrates that although blood pH remains within normal range in water deprived camels, the primary challenge to water deprived camels is a mild respiratory alkalosis induced by reduced blood pCO2 which may be the result of an accelerated respiratory rate.
November 13, 2011; Accepted: January 20, 2012;
Published: February 17, 2012
Camel is a suitable desert animal that inhabits arid and semi-arid environments
which are characterized by long periods of intense heat load and drought. Thermo-physiological
mechanisms that enable camels to cope with water deprivation are well documented
(Ayoub and Saleh, 1998; Al-Haidary,
2005, 2006; Abdoun et al.,
2010). To our knowledge there is only one report (Yagil
et al., 1975) on the impact of dehydration on acid-base status in
camel. This report included only blood pH and pCO2 as respiratory
acid-base parameters. The vital limits of pH variation for mammals are between
pH 7.36 and 7.44 (Houpt, 1989). Animals body utilizes
three basic mechanisms: Chemical buffering, respiratory adjustment of blood
carbonic acid and excretion of H+ or HCO3-
by the kidneys to combat any changes in the normal acid-base balance (Houpt,
1989). Water deprivation and dehydration are known to affect the concentration
of plasma albumin (Al-Haidary, 2005) and blood hemoglobin
concentration (Ayoub and Saleh, 1998) which could alter
the blood buffering capacity. Further, dehydration affects renal function (Yagkil,
1993) and is associated with increased urine osmolality, reduced urine production
and increased Na excretion (Ben Goumi et al., 1993).
Moreover, dehydration is known to increase respiratory frequency and minute
ventilation in camels (Schroter et al., 1987).
It has also been reported that dehydration could result in changes of plasma
cations and anions concentrations (Ayoub and Saleh, 1998;
Al-Haidary, 2005) which will be reflected on the alteration
of Anionic Gap (AG). Anionic gap that contributes to the acid-base balance varies
in response to changes in plasma concentrations of these components (Kirschbaum
et al., 1999). These effects of dehydration might have impact on
the acid-base balance. Therefore, the intention of this study was to investigate
whether camels could maintain their acid-base balance under prolonged water
MATERIALS AND METHODS
Five (2-years old) clinically healthy male dromedary camels were purchased from the local market and transported to Experimental Farm Unit affiliated to Animal Production Department, College of Food and Agriculture Sciences, King Saud University, Riyadh. Camels were housed individually in shaded pens, fed at 2.5% of their body weight twice a day at 7:00 and 16:00 h on a commercial mix formulated pellets diet (ME 1950 kcal kg-1, Crude protein 13%, Crude fat 2%, Crude fiber 10%, Ash 8% on DM basis) and had free access to clean tap water. During the experimental period water was with-held for 7 days.
Ambient temperature (Ta) was recorded continuously at 30 min interval using 2 data loggers (HOBO Pro Series data logger, Model H08-032-08, ONSET Co., USA) mounted at a height of approximately 2 m from the ground and placed away from direct sources of heat, sunlight and water. Special data logging software (BoxCar Pro 4, ONSET Co., USA) was applied for programming the loggers and for data analysis. The average daily ambient temperature (Ta) prevailed during the experimental period had a minimum value of 18.90±0.48°C and a maximum value of 39.21±0.75°C with an overall mean of 28.55±0.51°C.
Determination of the levels of blood acid-base parameters (blood pH, pCO2, pO2, HCO3-, tCO2, BE, O2 saturation) was carried on whole venous blood samples (~2.5 mL) collected by jugular venipuncture using heparin coated syringes (Terumo Co., Japan). Whole blood samples were analyzed within 1 h of collection using blood gas analyzer (Rapid System, Semense, USA). Respiratory rate was counted at the space from 9th to 11th rib using stethoscope (Littmann Stethoscope, USA) and expressed as breath min-1.
Statistical analysis: Statistical analysis of the data was performed using the software program SigmaPlot Statistics (SigmaPlot 11.0, Systat Software, Inc., San Jose, CA, USA). The changes in respiratory rate and acid-base parameters which occur after experimental dehydration on the same individuals was tested using paired t-test to determine whether or not the treatment (water deprivation) had a significant effect. By concentrating on the changes produced by the treatment instead of the values observed before and after the treatment, paired t-test eliminate the differences due to individual reactions which gives a more sensitive (or more powerful) test for finding an effect. The overall level for statistical significance was set at p<0.05. All values were presented as means±standard error of the means (Means±SEM).
Acid-base parameters of camels: During this study the blood acid-base
parameters of dromedary camels was determined using venous blood samples collected
from five adult apparently healthy camels.
|| Normal values of acid-base parameters in dromedary camels
||Post rehydration recovery of (a) respiratory rate and (b)
Table 1 shows the normal values of blood acid-base parameters
of dromedary camel. Blood pH ranged from 7.28-7.44 with mean value of 7.35±0.03,
pCO2 ranged from 41.40-57.90 with mean value of 49.50±4.46
mmHg, tCO2 ranged from 25.00-30.00 with mean value of 28.25±1.11
mmol L-1, bicarbonate ion concentration ranged from 23.50-28.30 with
mean value of 26.78±1.11 mmol L-1, base excess ranged from
-2.00-+4.00 with mean value of 1.25±1.25 mEq L-1, pO2
ranged from 23.00-26.00 with mean value of 24.25±0.63 mmHg and O2
saturation ranged from 32.00-49.00 with mean value of 39.00±3.36%.
Effects of dehydration on acid-base parameters: Water deprivation for 7 days resulted in a significant (p<0.01) elevation of the Respiratory Rate (RR) from 17.66±0.13 to 39.36±1.85 breath/min which is reflected in a significant (p<0.1) reduction of blood partial pressure of CO2 (pCO2) from 49.50±4.46 to 41.25±1.51 mmHg, blood total CO2 (tCO2) from 28.25±1.11 to 27.00±1.08 mmol L-1 and blood bicarbonate (HCO3-) concentration from 26.78±1.11 to 25.63±1.14 mmol L-1. While, Base Excess (BE) was insignificantly reduced from 1.25±1.25 to 0.50±1.32 mEq L-1. These resulted in a slight insignificant increase, albeit within the physiological range of blood pH from 7.35±0.03 to 7.40±0.01. Dehydration also resulted in a slight insignificant elevation of blood partial pressure of O2 (pO2) from 24.25±0.63 to 25.75±2.10 mmHg and that of O2 saturation from 39.00±3.63 to 46.25±5.25% (Table 2).
Post rehydration recovery of acid-base parameters: Rehydration of camels
resulted in a fast recovery of respiratory rate (from 39.36±1.85 breath/min)
and blood pH (from 7.40±0.01) to the pre-dehydration levels (18.71±0.26
breath/min and 7.35±0.03, respectively) within 3 to 6 hours post rehydration
(Fig. 1). However, other acid-base parameters (pCO2,
tCO2, HCO3¯, BE, pO2 and O2
saturation) did not completely recover to pre-dehydration levels till 48 h post
rehydration (Fig. 2a-f).
|| Effects of dehydration on Respiratory Rate (RR) and acid-base
parameters in dromedary camels (Means±SE)
||Post rehydration recovery of (a) pCO2, (b) pO2,
(c) O2 saturation, (d) tCO2, (e) HCO3-
and (f) BE
Knowledge of the acid-base status of camels is important for evaluating the
physiological and health status of this species. Apart from isolated references
to blood pH, pCO2 and Stewart variables (Yagil
et al., 1975; Elkhair and Hartmann, 2010)
little is known about acid-base status in camels. Blood acid-base parameters
of camels are reported for the first time in this study. The blood acid-base
parameters of camels reported in this study were revealed using venous blood.
It has been reported that venous blood samples are in most cases sufficient
for the evaluation of uncomplicated acid-base disorders (Meintjes
and Engelbrecht, 1995). The reported levels of blood acid-base parameters
in camels differ from that reported in arterial blood of cows (Piccione
et al., 2004), venous blood of steers (Parker
et al., 2003) and venous blood of sheep (Srikandakumar
et al., 2003; Sobiech et al., 2005).
However, similar to that reported in venous blood of white-tailed deer (DelGiudice
et al., 1994).
Since the increase in body core temperature is known to stimulate both minute
ventilation and respiratory rate (Schroter et al.,
1987, 1989). The observed water deprivation induced
significant (p = 0.001) increase in respiratory rate of camels could be a reflection
of the dehydration induced elevation of body core temperature (Al-Haidary,
2005). Precise regulation of blood acid-base balance is vital because the
activities of almost all enzyme systems in the body are influenced by the H+
concentration (Fraser, 1991). Although water deprivation
tended to elevate blood pH (p = 0.14) in dromedary camels, the increase is within
the normal range reported in this study (Table 1). However,
water deprivation caused a tendency towards respiratory alkalosis and is most
probably due to hyperventilation and the subsequent significant (p = 0.07) decrease
in pCO2 due to increased elimination of CO2 (Table
2). The CO2 eliminated is derived from carbonic acid (H2CO3)
which dissociates to form CO2 and H2O. The HCO3-
is converted to H2CO3 by receiving H+ from
the buffer systems, such as hemoglobin, plasma proteins and extra cellular fluid
phosphates which resulted in the observed significant (p = 0.03) reduction of
HCO3- concentration. During respiratory alkalosis, a decrease
in plasma HCO3- would be expected. Where, the body tries
to compensate for the respiratory alkalosis by excreting HCO3-
through the kidneys and retaining H+ ions. This could be supported
by the reported elevation of aldosterone concentration in the blood of water
deprived camels (Abdoun et al., 2010) which is
known to stimulate H+ secretion by intercalated cells in the collecting
duct, regulating plasma bicarbonate (HCO3-) levels and
its acid/base balance (Rector and Brenner, 2004). To support
respiratory alkalosis, urine samples should have been collected for urine pH
Physiological systems attempt to maintain homeostasis so that BE (the deviation
of buffer base of blood from the normal value) remains near zero. In this study
Base Excess (BE) was maintained near zero after 7 days of water deprivation.
Venous blood pO2 and O2 saturation tended to increase
due to water deprivation. This could be the result of the reported reduction
in feed intake and metabolic rate in water deprived camels (Fowler,
2010). Although, respiratory rate and blood pH returned to control values
within 3 h of rehydration, respiratory acid-base parameters did not completely
return to control values during 48 h post rehydration.
The results reported in this study identified reference values of acid-base parameters that can be used for the clinical diagnosis of acid-base disturbances in camels. Further, when dromedary camels were subjected to water deprivation, they were still able to maintain a normal acid-base balance despite the significant acceleration of their respiratory rate.
This study has been supported by the National Plan for Science and Technology (NPST) program by King Saud University, project number 09-BIO 885-02.
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