Thermoregulation & Water Balance by Rahardja Et Al

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Aninal(20111,5:10, pp 1587-1593 @ The Animal Consortium 2011doi:1 0.1 01 7/51 751731111000577 animal

Thermoregulation and water balance in fat-tailed sheep andKacang goat under sunlight exposure and water restrictionin a hot and dry areaD. P. Rahardjat, A. L. Toleng and V. S. LestariAnimal Physiology Laboratory, Animal Agriculture Faculty, Hasanuddin University - Makassat 90245 South Sulawesi, Indonesia

(Received 23 May 20'10; Accepted 15 March 2011; First published online 15 April 2011)

The objective of this study was to analyze differences in thermoregulation and water balance under conditions of heat loadand water restriction between fat-tailed sheep (S) and Kacang goats (G). The daily intakes of food and wate4 daily outputs ofurine and feces, rectal temperature, respiration rates, hematocrit values and plasma volumes of five shorn S and five G weredetermined over 1 0 days of four consecutive experimental conditions: (1) indoor - unrestricted water; (2) indoor - restrictedwater; (3) 10 h sunlight exposure - unrestricted water; and (4) 10 h sunlight exposure - restricted water There was a 6- to 7-dayadjustment period betvveen two consecutive conditions. The study was conducted during the dry season. The animals were placedin individual cages, fed chopped native grass ad libitum and had free access to a urea-molasses multi-nutrient block. IJndersunlight exposure with unrestricted water availability S and G record an increase in the maximum rectal temperatures from39.2"C to 40.2"C and from 39.9"C to 4l.8"C, respectively. The thermoregulatory strategy used by 5 for maintaining a lower rectaltemperature mostly depends on increasing the respiration rate as the main cooling mechanism. On the other hand, G apparentlyused sweating as the predominant mechanism for cooling. MoreoveL G seemed to be more tolerable to higher heat storage andbody temperature than S with a significant increase in plasma volume (P < 0.01), and this may be beneficial to the animals forthe prevention of water loss. Under restricted water condition in either indoor or outdoor environment, both species decreasedtheir plasma volume significantly, but rectaltemperatures were relatively maintained. ln all experimental conditions, the daily totalwater exchanges (nt/kgf'82 per day) of S were significantly higher than G (P < 0.01,). However; when the percentages of the totaldaily water exchange were considered, the water lost through urination (38% to 39%), defecation (1 I % to l4%) and evaporation(46% to 49%) by S and G was not significantly different. Therefore, the results from this study clearly showed that S and G havedifferent homeostatic strategies for the regulation of body temperature and fluid to cope with heat load and water restriction.These differences may have an important impact on the production management of S and G.Keywords: sheep, goat, water balance, thermoregulation, plasma volume

lmplicationJeneponto, in South Sulawesi, lndonesia, is known to bethe hottest and driest regency of the area, Under theseconditions, fat-tailed sheep and Kacang goats are faced withhigh environmental temperatures and water scarcity. How-evel these animals are raised by small herders using samemanagement strategies, as the farmers do not recognizethe characteristic differences between these two species.Therefore, this study was designed to elucidate these dif-ferences, especially in their water balances and thermo-regulation abilities. Understanding these characteristics is

needed to boost the small herder incomes and to improvethe rural farmer livelihood in this region.lntroductionEnvironmental stress because of high temperature and/orwater restriction has long been recognized as an importantconstraint for animal production in many parts of lndonesia.ln South Sulawesi, lndonesia, Jeneponto is well known asone of the hottest and driest regions with an annual rainfallof less than 200 mm over 63 rainy days per year. Moreove;the daily temperature fluctuates between 17"C and 42"C.This climate may have both direct and indirect negativeeffects on animal production. However, the population ofE-mail: djoniprawira@yahoo com

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Rahardja, Toleng and Lestarisheep and goats is denser than other regions. lt appearsthat these two species of small ruminants have been welladapted to thrive in the harsh environment of Jeneponto,including the climate conditions as well as nutrient andwater availability. This observation seems to conflict withnumerous comparative studies that have suggested thatgoats are superior to sheep in thermoregulation, digestion,water balance and adaptive abilities (El Nouty et al., 1988;Silanikove, 1 992; Silanikove, 2000a).The determination of daily water exchange betweenanimals and their environment is important for estimatingwater requirement as well as for evaluating their adapt-ability and productivity (Silanikove, 2000a and 2000b). Thestrategies used by these two species to adapt to the physicalconditions of Jeneponto are intriguing, lt is possible that thetwo species have the same level of water economy and lessthermal discomfort. However, it is unknown whether sheepand goats use the same physiological strategies to counter-act the climatic condition of Jeneponto. Therefore, this studywas conducted to elucidate water balances and thermo-regulation strategies used by sheep and goats under sunlightexposure and restricted water availability.

Material and methodsFive shorn fat-tailed sheep ewes (S) between 2 and 3 years andfive Kacang goat does (G) between L5 and 2 years were usedin this study. At the commencement of the study, the bodyweights of 5 and G were 26.98 -r 1 .3 and 16.92 -r 1 .14 kg, andat the end of the study their body weights were 26.65 t- 1.74and 15.30 )- 1.25 kg, respectively. Both species originated fromJeneponto Regency, South Sulawesi, lndonesia.

The animals were individually placed in specifically con-structed cages that had food and water containers in thecages, as well as feces-urine separators beneath the cages.The animals were fed chopped native grass and had accessto a urea-molasses multi-nutrient block (UMMB; Foodand Agriculture 0rganization, 2007) ad libitum throughoutthe experiment. All animals were orally dosed with an anti-helminthic and intramuscularly injected with vitamin B-complexas well as a high dose of vitamin A shortly after being placedin the cages.

The experiment was conducted during the dry season.Table 1 shows that there were four treatment periods of10 days each. Before collecting data for each period, the

animals were allowed to acclimatize to the treatment con-ditions until the daily intakes of food and water wereapproximately constant, and a steady-state body tempera-ture was obtained. lt was assumed that a steady state wasachieved when rectal temperature and respiratory rateremained constant for at least I h (within a range of 0.2'Cand l0 respirations/min, respectively).

Total water intake was calculated daily as the sum of dailyconsumed wate[ water contained in ingested food (pre-formed water) and metabolic water. The preformed waterfrom native grass and UMMB was determined separately bydrying the samples at 80'C for 48 h, and then cooling themin desiccators for B h to achieve a constant weight as well asto determine the content of fecal water.

The metabolic water from digestible organic matter (pro-tein, carbohydrates and fat) was estimated for each animalon the last 5 days for each period. The amount of metabolicwater was calculated by multiplying the amount of eachdigestible organic matter (protein, carbohydrates and fat) byfactors of 0.41, 0.60 and 1.07, respectively, and by calcu-lating the sum of these values (Brody, 1 945).

Evaporative water loss was estimated by subtracting thesum of fecal and urinary water loss from the total daily waterintake, Evaporation from the drinking water in the vessel andingested grass was corrected daily,

Urine and fecal.outputs of each animal were monitoredthree times a day for each period, whereas a 10% pooledsample of urine and feces was collected each day. Dried foodand fecal samples were finely ground to pass a 1 mm screenand were stored in sealed polyethylene containers for sub-sequent analysis. The organic matter content of the foodor feces was calculated by subtraction of the ash contentfrom the known weight of the food or feces sample; the ashcontent was determined by ignition of samples for 6 h at550"C. Crude protein, fat and carbohydrate (fiber- andnitrogen-free extracts) contents of the food and feces weredetermined using the procedures of the proximate analysis(Association of Official Analytical Chemists, 1990).

Rectal temperatures and respiration rates were monitoredfour times each day at 0600, I I 00, 1 400 and 1 600 h. Rectaltemperatures were measured using a digital thermometer(accuracy -+0.1'C) inserted at a -r5cm depth into therectum. The respiration rates were determined by countingflank movements over a set period of time with the aid of astopwatch.

Table 1 Environmental condition and water availability during four consecutive periods of experiment of l0 days each

Experimental condition

Environment lndoor (18'C to 30"C and 60% to 70% RH)Outdoor (sunlight exposure for I 0 h/day; 'l 8"C to 39.3"C

and 40% to 60% RH)

Unrestricted (control) Restricted (50% of intake in thefirst period) Restricted(50% of intake in thethird peiiod)Unrestricted

RH : relative humidity.1 588


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Plasma volume was determined on the last day of eachperiod at 1600 h using the dilution technique of Evan Blue, inaccordance with'the procedures previously described byWilliams et al. (19911.

The research was arranged as a factorial experiment of2 x 4 with five replications and one factor as repeated mea-sures; the first factor was species (S and G) and the secondfactor was period (four measurement periods). The analysisof variance for data and Duncan's multiple range test forsignificant differences of mean values were performed byusing the computer statistical package 'SYSTAT for Windowsversion 6' (SPSS lnc., Chicago, USA; Wilkinson, 1996).

ResultsPhysiological parametersThe effects of sunlight exposure and water restriction onseveral physiological parameters, including plasma volume,hematocrit value, rectal temperature and respiration rates,are shown in Table 2.

Direct exposure to sunlight did not significantly changebody weights of S and G that had restricted or unrestrictedwater availability. The reduction of water intake significantlydecreased the body weights of G in both environmentalconditions (P


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Rahardja, Toleng and LestariTable 3 The effects of sunlight exposure and water restriction on the intakes and digestibility of organic matter of 5 and G

Parameters Species anddifference

Experimental conditionlndoor (18"C to 30'C and 60% to 70% RH) Outdoor (18'C to 39'C and 40% to 60% RH)Unrestricted water Restricted water Unrestrictedwater Restrictedwater

Organic matter intake(g/kgo tt per day)

Organic matter digestibility (%)

Digestible organic matter(g/kgo tt per day)

5GSv.GSGSUGSGSv.G

53.29 -r 5.97"55.47 -ts 2.92"

ns50.95 -f 0.84452.46 -f 0.88"27.20 )- 3.46"29.14 -r 1.33"

ns

43.44 + 21gb42.89 -r 4.28b

ns53.95 -r 2.52b57.70 ! 1.47b24.42 -r 1.07b24.76 -r 2.70b

n5

47.14 -r 3.01c55.52 + 2.91"55.10 -f 2.02b55.24 -f 2.09b

ns25.94'r 1.1fb30.73 -f 2.18"

38.32 -r 3.28d42.85 -f 2.83b62.00 -f 2.00c63.48 + 0.87c

n523.78 -f 2.50b25.95 + 2.10b

nsS : fat-tailed sheep; G : Kacang goats; RH : relative humidity.Means with different superscript letters at the same variable within the same row of S or G are significantly different at P< 0.05; S u G differences at *P< 0.05and **P< 0.01.

Both species increased water consumption when the dailymaximum air temperature increased to 39'C.ln all experimental conditions, the loss of water (g/kg0'82per day) through urination, defecation and evaporation by Swas markedly higher compared with G (P< 0.01). However;the proportions of total water loss by urination, defecationand evaporation were comparable between both species.These proportions changed when the maximum air tem-perature was increased (from 30'C to 39'C), but did notchange when drinking water was reduced to 50% of thead libitum level.Fecalwater lossThe fecal water loss accounted for the smallest fractionof total water loss in S and G compared with the othermechanisms of water loss. The amount of fecal water losswas higher in S than in G when expressed as g/kg0'82 perday. Howeve; both species had comparable proportions oftotal water loss under all experimental conditions. At amaximum air temperature of 30'C, the proportion of thefecal water losses of both species ranged between 12o/o and15o/o of the total water loss, whereas at a maximum airtemperature of 39'C the proportion of fecal water lossdecreased significantly to 5% to 7o/o (P


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Heat and water balances of sheep and goats

Table 4 Effects of sunlight exposure and water restriction on water balance of 5 and G

ParametersSpecies anddifference

Experimental conditionlndoor (18'C to 30'C and 50% to 70% RH) Outdoor (18'C to 39'C and 40% to 60% RH)Unrestricted water Restricted water Unrestrictedwater Restrictedwater

Water intakes121.96t234h 397.65 -f 19.70'ngested water (g/kgo 82 per day)Preformed water (g/kgo 82 per day)

Estimated metabolic water(g/kgot' per day)

ln urine (g/kgo 82 per day)

ln urine (% total water loss)

ln feces (g/kgo 82 per day)

ln feces (% total water loss)

Estimated evaporative water(g/kgo'" per day)

Estimated evaporative water(% total water loss)

sGSv.GsGSUGSGSv.G

242.71 '+ 11.58"133.881 10.13"

32.79 -r 1.8f34.63 + 1.314

n56.91 -f 1.1847.94 -r 0.22"

n5

109.38 t 6.91 "71.10 -r 9.76"38.98 -f 1.09438.31 -'- 4.574

n540.97 !2.74"27.04 + 1.67"14.64 ! 1.49"14.60 + 0.98"

ns130.14 -f 8.144

87.14 -r 7.90446.38 -t 4.23"47.09 a 4.88"

ns

64.13*-f 3.76b26.38 -r 0.37b26.58 -'- 1.59b

n56.50 a 1.7347.49 + 0.924

n5

251 .11 + 9.63c28.17 -r 0.67'35.85 -r 1.32"

7.44 -r 0.53"10.03 -f 0.63b

211.28+ 14.94d132.96 t 13.50"21.89 -l- 1.66d25.28 ! 1.72b10.39 -f 1.10b12.77 !0.92'

41.44 -r 3.40d28.96 !2.21d'16.99 + 2.69b17.16 -r 2.55b

ns23.83 + 3.45b

8.50 r 0.40d5.68 r 0.78b5.03 -f 0.65b

ns178.30 + 10.66d131.54 rt 12.09d

77.34-+ 5.66h77.81 -f 6.53b

n5

Water losssGSv.GSGStzG5GSv.GSGStzGSG5uG5GStzG

60.36 -f 3.24b41 .69*-{. 4.68b39.33 t 2.58438.82 + 3.90"

n521 .15 -f 1.65b12.85 -f 0.82b13.12 a 1.15411.97 -f L86"

n574.33 -r 436b52.g5*r- 5.39b47.55 -r 3.73449.21 -r 4.244

ns

81.04 r 8.26c53.321 6.05'18.70 -f 3.13b19.42'r z.yb

ns28.05 t ',|.90c20.221 0.58c

6.49 r- 0.36b6.97 -r 1.20b

n5324.18 + 12.43'215.66 -r 13.56'

74.90 -r 7.28h74.61 -r 4.63h

ns5 : fat-tailed sheep; G : Kacang goats; RH : relative humidiry.Means with different superscript letters at the same variable within the same row of S or G are significantly different at P< 0.05; S tz G differences at *P< 0.05and **P< 0.01.

basal conditions (control) are heat stressful. These results mayalso reflect physiological differences between breeds adaptedto semi-xeric condition (Merino) and breeds adapted to hottropical environments (S of Jeneponto).ln G, alterations in plasma volume were apparentlyin proportion to the thermoregulatory requirement. Thisresponse seems to be similar to those found in desert-adapted goats (El Nouty ef a/., 1988; Silanikove,2000a). Wehypothesize that this is a strategy of G having smaller bodysize compared with S as a mechanism for coping with thehigh environmental temperature.

A significant increase in plasma volume in G should occurconcomitantly with an inirease in the total amount of bodywater (TBW), as the plasma is a component of the extra-cellular fluid. Previously, Taymour et al. (19841showed thatheat stress increased TBW of the goats by about 8%, whichis comparable with the increased plasma volume observed inour current study.

Accordingly, our present results indicate that heat loadmay also increase TBW in G, whereas it was relatively stablein S. Therefore, G seem to be more tolerable to higher heatstorage and body temperature than S, and this may bebeneficial to the animals for the prevention of water loss.

ln this study, S and G showed different mechanisms for thedissipation of excessive heat because of an increase in airtemperature. The basic mechanism for cooling is the eva-poration of water from the respiratory tract (panting) andbody surface (sweating; Silanikove, 2000b; Robertshow,2004). The present results showed that in addition to anincrease in body temperature, an increase in air temperatureresulted in a remarkable increase in the respiration rate ofboth species. 5 had an 11{old increase in the respiration ratecompared with the basal conditions. ln G, however, a 5- to6-fold increase was observed compared with basal condi-tions, An increase in the respiration rate leads to an increasein the ventilation rate, which causes an increase in heat loss


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Rahardja, Toleng and Lestarifrom the respiratory passage (Joshi et al., 1977). Both spe-cies apparently used panting and sweating as a mechanismfor cooling, and S used panting as the main evaporativecooling system, which is consistent with the general patternfor this species (Silanikove, 2000b). 0n the other hand, Gused sweating as the main evaporative cooling system(Dmi'el, 1986; Baker and Nijland, 1993). Reduced sweatingduring dehydration and/or excessive heat storage resultedin increased body temperature and selective brain cooling(Dmi'el, '1986; Bakernd and Mijland, 1993), which mostlikely relates to the thermolability observed in G from thepresent experiment.Moreove[ the increase in the respiration rate observedin S may have more homeostatic relevance, in addition tothe higher daily total water exchange, for the dissipationof excessive heat and the maintenance of a lower bodytemperature compared with G.

An increase in ambient temperature resulted in reducedfeed intake, which was most likely due to the metabolic rateof S, as noted by Silanikove (1992). This may be attributableto a reduction in thyroid secretion as well as gut motility,which leads to an increase in gut fill (Abdullah and Falconel1977). Therefore, it is reasonable to hypothesize that theappetite reduction of S under heat load may be primarily dueto an elevation in body temperature. ln addition, it may alsobe related to an increase in gut fill and a slower passage rateof digested material in the gastrointestinal tract.ln addition, a reduction in feed intake by S occurredsimultaneously with an increase in water consumption.Howevel under this condition, G appeared to maintain aconstant consumption of both food and water.

There is a positive relationship between digestibility andambient temperature, which would be expected from theslower rate of passage (Christopherson and Kennedy, '1983).Under heat stress, both species showed a similar increase intheir digestibility. However; because S had a lower intake oforganic matter than G, the digested organic matter was alsolower. As a consequence, it may have resulted in a lowermetabolic rate, heat production and body temperature in Sthan in G.

Previous studies have shown that the water content in therumen tends to increase when water consumption increases,and the water turnover rate accelerates in goat (Silanikove,'1989), sheep (Degen and Shkolnik, 1978), cows (Silanikoveand Tadmore, 1989) and swamp buffalo (Chaiyabutr et a/.,1987). The increased water content in the rumen was used tocounterbalance water losses from the systemic fluid duringdehydration.

The reductions in the plasma volume of S and G resultedfrom water restriction in either the indoor or outdoor conditions,and suggested that the release of vasopressin increased. Anincrease in vasopressin levels would suppress food intake(Purohit et al., 1972; Meyer ef al., 1989) and increase waterre-absorption from the kidneys (Molony eta1.,1987; Sand ef a/.,1 987) as well as from the last part of the gut (Robertson, I 984).Under control conditions, S and G had a total waterexchange of approximately 280 and 175 ml/kgo 82 per day,

respectively. When S and G were exposed to heat load, theirdaily water exchange increased to 430 and 295ml/kgo82,respectively, which showed that the water balance increasedto a higher level than under the control conditions. Theseresults could be attributed to the remarkable water economyexhibited by G as compared with S, which may have to dowith the origin of the goats. Silanikove (2000a) suggestedthat goats originated from and adapted to hot and dry areasof the world, and that their water economy may be moreefficient than other ruminants.As expected, the daily total water consumption in bothspecies increased at the daily maximum air temperatureof 39'C. Howeve4 in relation to the organic matter intakeand digestibility, the additional water (metabolic water andpreformed water) in S was reduced, whereas in G theseadditional water amounts were relatively stable. Bothspecies had a reduction in urinary and fecal water lossesas well as in the amount of water per 100 g of fecal drymatter. ln contrast, the water lost by evaporation remarkablyincreased.

The above discussion indicates that a simple physiologicalmechanism does not explain the remarkable tolerance ofsheep and goats to heat stress and to low water availability.Sheep and goats that live in the harsh environment ofJeneponto may be able to withstand and adapt to the con-ditions because of their own mechanisms of heat and waterbalances.

The results clearly showed that under sunlight exposurewith unrestricted water availability, S and G increasedtheir maximum rectal temperatures from 39.2"C to 40.2'Cand from 39.9"C to 41.8"C, respectively. Thermoregulatorystrategies of S for maintenance of a lower rectal temperaturemostly depend on increasing respiration rate as the mainmechanism for dissipating excessive heat load. 0n the otherhand, G apparently used sweating as the main coolingmechanism. Moreovel G seems to be more tolerable to ahigher heat storage and body temperature than S, as therewas a significant increase in plasma volume. This may bebeneficial to the animals for the prevention of water loss. lnall experimental conditions, the daily total water exchanges(ml/kgo 82 per day) of S were higher ihan G. As a percentageof the daily total water exchange, however, the waterlosses through urination (38% to 39%), defecation (12% to15%) and evaporation (460/o to 49o/o) by S and G werenot significantly different. Under conditions of sunlightexposure, the water lost through urination and defecationwas decreased lo 17o/o lo 19o/o and 5% lo 7o/o, respectively,whereas the loss through evaporation increased to 75o/oto 78o/o.Conclusion5 and G have developed different homeostatic mechanismsof thermoregulation and water balance to cope heat stresswith or without concomitant scarcity of water. Differentmechanisms may have an important impact on produc-tion management for improving productivity in the harsh


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environment of Jeneponto. The sheep with its own mechanismrequired more water compared with that of the goat. lt may bebeneficial for both species to lower their heat loads during thewarmest hours of the day, thereby reducing the detrimentalimpact of thermal strest such as by changing the time offeeding to the late afternoon.

AcknowledgementsThis work was supported by a grant from the Ministry ofNational Education - Directorate General of Higher Education -lndonesia.

ReferencesAbdullah R and Falconer lR 1 977. Response of thyroid activity to feed restrictionin the goat. Australian Journal of Biological Sciences 30, 207-215.Association of Official Analytical Chemists (AOAC) 1990. Official methods ofanalysis, 15th edition. AOAC, Washington, DC, USA.Baker MA and Nijland MJM 1993. Selective brain cooling in goats - effects ofexercise and dehydration. journal of Physiology (London) 471,679_f.92.Brody S 1 945. Bioenergetic and growth, with special reference to the efficiencycomplex in domestic animals. Reinhold Publishing Corporation, New York, NYUSA.Chaiyabutr N, Buranakarl C, Muangcharoen V, Loypetlra P and PichaichanarongA 1987. Effects of acute heat stress on changes in the rate of liquid flow fromthe rumen and turnover of body water of swamp buffalo. Journal of AgriculturalScience (Cambridge) 108, 54F553.Christopherson RJ and Kennedy PM 1983. Effect of thermal environment ondigestion in ruminanG. Canadian Journal of Animal Science 63, M7496.Dmi'el R 1 986. Selective sweat secretion and panting modulation in dehydrationgoats. Journal of Thermal Biology I 1, 157-692.Degen AA and Shkolnik A 1 978. Thermoregulation in fat-tailed Awassi, a desertsheep, in German mutton Merino, a mesic sheep. Physiological Zoology 5'1,333-339.El Nouty FD Hassan GA, Taher TH, Samak MA, Abo-Ellezz Z and Salem MHI 988. Water requirement and metabolism in Egyptian Barki and Rahmani sheepand Baladi goats during spring, summer and winter seasons. Journal ofAgricultural Science (Cambridgel 111, 27-34.Food and Agriculture Organization (FAO) 2007. Feed supplementation block,urea-molasses multinutrient blocks: simple and effective feed supplement

Heat and water balances of sheep and goatstechnology for ruminant agriculture, paper 164. FAO Animal Production andHealth, Rome, ltaly.Joshi BC, Aravindam M, Singh K and Bhattacharyya NK'1977. Effect of highenvironmental stress on the physiological responses of bucks. lndian Journal ofAnimal Sciences 47, 200-202.Meyer AH, Langhani W and Scharrer E I 989. Vasopressin reduces food intake ingoats. Quarterly Journal of Experimental Physiology 74,465-473.Molony DA, Reeves WB, Hebert 5C and Androli TE 1987. ADH increases apicalNa*, K*, 2Cl- entry into mouse medullary thick ascending limbs of Henle.American Journal of Physiology 252, F177-F180.Purohit GR, Ghosh PK and Taneja GC 1972. Water metabolism in desert sheep,effects of various degrees of water restriction on the distribution of body waterin Mawari sheep. Australian Journal of Agricultural Research 23, 685-691.Robertshow D 2004. Temperature regulation and thermal environment.ln Duke's physiology of domestic animals (ed. W0 Reece), pp. 962-973.Comstock Publishing Associates, Cornell University Press, lthaca and London.Robertson GL 1984. Abnormalities ofthirst regulation. Kidney lnternational 25,460-469.Sand JM, Nonoguchi H and Knepper MA I 987. Vasopressin effects on urea andH20 transport in inner medullary collecting duct sub-segments. AmericanJournal of Physiology 253, F823-F827.Silanikove N 1987. lmpact of shelter in hot Meditenanean climate on feedintake, feed utilization and body fluid distribution in sheep. Appetite 9,207-215.Silanikove N 1 989. lnter-relationship between water, food and digestible energyintake in desert and temperate goab. Appetite 12, 163-170.Silanikove N 1992. Effects of water scarcity and hot environment on appetiteand digestion in ruminants: a review. Livestock Production Science 30, 175-194.Silanikove N 2000a. The physiological basis of adaptation in goats to harshenvironmenB. Small Ruminant Research 35, 181-193.Silanikove N 2000b. Effects of heat stress on the welfare of extensivelymanaged domestic ruminants. Livestock Production Science 67, l-1 8.Silanikove N and Tadmore A 1989. Rumen volume, saliva flow rate and systemicfluid homeostasis in dehydrated cattle. American Journal of Physiology 256,R80FR815.Taymour KH, Kamar GAR, Gabr HA and El-Masry KM 1984. Water balance ingoats maintained under mild and hot weather. Egyptian Journal of AnimalProduction 24, 237 -246.Wilkinson L 1 996. Statistics: Systat 6.0 for Windows. SPSS lnc., Chicago, lL, USA.Williams AJ, Thornberry KJ and Nicol H 1 991 . A comparative investigation of thevolume of plasma and extracellular fluids and renal clearance of urea andcreatinine in Merino sheep from flock with genetic capacities for wool.Australian Journal of Agricultural Research 42, 1311-1321.

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Thermoregulation & Water Balance by Rahardja Et Al