journa l homepage: www.e lsev ier .com/ locate /smal l rumres
esponses to saline drinking water in offspring born to ewes fed highalt during pregnancy�
.N. Digbya,d,∗, D. Blachec,d, D.G. Mastersb,d, D.K. Revell a,b,d
Discipline of Agricultural and Animal Science, School of Agriculture, Food and Wine, The University of Adelaide, Roseworthy, SA 5371, AustraliaCSIRO Livestock Industries, Private Bag 5, Wembley, WA 6913, AustraliaSchool of Animal Biology M085, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway,rawley, WA 6009, AustraliaFuture Farm Industries Cooperative Research Centre M081, Faculty of Natural and Agricultural Sciences, The University of Western Australia,5 Stirling Highway, Crawley, WA 6009, Australia
r t i c l e i n f o
rticle history:vailable online 25 February 2010
eywords:aline wateralt and water balanceeed intakeetal programming
a b s t r a c t
We have studied the fetal programming of lambs born to ewes exposed to high salt duringpregnancy. In the present study, we hypothesise that salt-programmed lambs may notneed to drink as much saline water as control lambs and that voluntary feed intake ofsalt-programmed lambs would be reduced. We used two groups of lambs born to ewes fedeither a high salt (13% NaCl) diet during pregnancy (S-lambs; n = 12) or control animals bornto ewes fed a conventional (0.5% NaCl) diet during pregnancy (C-lambs; n = 12). Animalswere offered ad libitum amounts of saline drinking water containing 1.5% NaCl for 2 days.Results indicated that there was a significant difference between fetal origin of the lamb(i.e. between C and S-lambs) and time (day 1 and 2) on water intake (P = 0.055), urinaryoutput (P = 0.002), and sodium excretion (P = 0.002). There was an interaction between fetalorigin of the lambs and time (day 1 and 2) on the area under the curve (AUC) for theplasma concentration of aldosterone (P = 0.017). Aldosterone concentration for C-lambsranged from 167 to 196 pg/ml over days 1 and 2, whilst S-lambs reduced their aldosteroneby two-thirds from day 1 to 2, from 214 ± 24 to 74 ± 8 pg/ml. A novel result was a marked
difference in feed intake between C and S-lambs, where S-lambs consumed approximately0.5 kg DM/day (35%) less than C-lambs which was associated with a decrease in insulinsecretion with time in both S and C-lambs. In conclusion, feeding a high salt diet to pregnantewes affected the physiological responses of their offspring to the consumption of salinewater during a period of 2 days illustrating that fetal programming changed the temporalpattern of how the offspring adapt to a load of ingested salt.
� This paper is part of a special issue entitled: Potential use of halo-hytes and other salt-tolerant plants in sheep and goat feeding, Guestdited by Hichem Ben-Salem and Pierre Morand-Fehr.∗ Corresponding author. Present address: Liggins Institute, The Univer-
ity of Auckland, Ngapouri Research Farm, Reporoa, 2739 State HighwayRD2 Reporoa 3083, New Zealand. Tel.: +64 7 333 8493; fax: +64 7 333
The use of halophytic plants such as saltbush repre-sents one of the few viable options to revegetate salinelandscapes and re-establish profitable grazing systems
(Masters et al., 2007). Halophytic plants are being used asa feed source when pasture availability is reduced, such asduring the summer/autumn feed gap (Masters et al., 2006).The shrubs (e.g. saltbush and bluebush) can contain over20% of salt in their edible parts (Wilson, 1975) and inges-
tion of high levels of salt can have a variety of negativeeffects on both production and physiology. Understandingthe physiological mechanisms underlying the capacity ofsheep to adapt to an ingested salt load is a necessary stepto develop sustainable strategies to raise sheep on salineland.
In sheep, exposure to high salt load induces two majorhomeostatic responses: an increase in water intake anda decrease in food intake (Peirce, 1957; Wilson, 1966a,b;Wilson and Hindley, 1968; Masters et al., 2005; Blacheet al., 2007). Collectively, an increase in water intake andincreased rate of real excretion of sodium and chlorideions suggest that continual exposure to salt can triggeradaptive responses and affect the capacity of sheep tomanage ingested salt loads (Potter, 1961, 1963, 1968). Inaddition to an effect on energy intake, high salt consump-tion also regulates energy partitioning in sheep (Blache etal., 2007) possibly by a direct effect on insulin concen-trations. Insulin decreased in response to salt intake forwethers (Blache et al., 2007) and pregnant ewes (Digbyet al., 2008), independent of feed intake. Moreover, therenin–angiotensin system, which controls osmolarity, mayplay a role in regulating feed intake (Blair-West and Brook,1969; Sunagawa et al., 2008). In ruminants, changes inplasma osmolarity can influence feeding behaviour in asimilar way as dehydration (Utley et al., 1970; Baile andDella-Fera, 1981). In addition, an increase in the activ-ity of the renin–angiotensin system, specifically increasedangiotensin II, is associated with increased energy expen-diture in rats (Cassis et al., 2002) and reduced feed intakein sheep (Sunagawa et al., 2001).
High salt intake during gestation is known to affectthe offspring (‘salt-programmed offspring’) including alter-ations in the thirst threshold, aldosterone concentrationsand hormonal control of energy balance (Digby et al., 2009).Also, ‘salt-programmed offspring’ have been shown to con-sume less of a concentrate diet (Chadwick et al., 2009).The reason for this lower voluntary feed intake is notknown. It could be linked to a reduced thirst threshold(Digby et al., 2009), but this would more likely reducewater intake and ruminal distension and remove a limi-tation to feed intake. An alternative mechanism could bethrough endocrine changes since salt ingestion can affectinsulin (Blache et al., 2007) and leptin (Digby et al., 2008),but we did not find a difference in insulin or leptin in‘salt-programmed offspring’ when they were exposed to aone-off oral salt challenge (Digby et al., 2009). A third pos-sibility is that ‘salt-programmed offspring’ have a higherretention of salt following ingestion (Digby et al., 2009) andexperience a negative association between the activity ofthe renin–angiotensin system and feed intake.
Up to now, to study the consequences of fetal program-ming by exposure of pregnant ewes to high salt, we havechallenged the offspring to one-off oral salt loads or a highconcentration of salt in feed and allowed them to have adlibitum access to fresh water. However, in field conditions
fresh water may not be available and sheep grazing salinelands may drink water containing salt ranging from 0.9%to 1.7% NaCl (Peirce, 1957). It is not known how sheepprogrammed by prenatal exposure to salt would respondto complete replacement of fresh water with saline water
esearch 91 (2010) 87–92
(1.5% NaCl). We hypothesised that (i) ‘salt-programmedoffspring’ may not need to drink as much saline water ascontrol offspring because their thirst threshold is higherand their altered hormonal balance is favourable to saltretention and (ii) within a day, the voluntary feed intakewill decline in ‘salt-programmed offspring’ because oftheir higher retention of salt and the negative associationbetween the activity of the renin–angiotensin system andcontrol of energy intake and energy partitioning.
2. Materials and methods
2.1. Experimental design
We used 2 groups of Merino lambs at 8 months of age, born toewes fed either a high salt (13% NaCl) diet during pregnancy (S-lambs;n = 12) or control lambs born to ewes fed a conventional, normal salt(0.5% NaCl) diet from conception through to parturition (C-lambs; n = 12).These animals were the offspring from a previous experiment reportedby Digby et al. (2008). The weights of the C and S-lambs were not dif-ferent at birth (4.8 ± 0.15 and 4.9 ± 0.17 kg) or at weaning (35.2 ± 0.48and 33.6 ± 0.62 kg). Digby et al. (2008) describes the maternal diets andewe management, and data on maternal hormone concentrations. From 2weeks after birth until weaning, lambs and ewes grazed pastures. Animalswere housed in individual pens adjacent to other animals in a photope-riod and temperature controlled purpose built shed at The University ofAdelaide, Roseworthy Campus. For experimental studies animals whereplaced in metabolism crates. During the experiment all animals wereoffered 1 kg of lucerne chaff and 500 g of sheep pellets each day; 8.5%crude protein; 8.5 MJ ME/kg; 0.5% NaCl; J.T Johnson and Sons, Kapunda,S.A. The University of Adelaide’s Animal Ethics Committee approved theexperiments.
The lambs were provided with 3 days adaptation to metabolism pensand then offered ad libitum amounts of saline drinking water containing1.5% NaCl for 2 days. Evidence from previous experiments (Digby et al.,2009) showed approximately 60% of a single salt load administered orallywas excreted within 23 h. Therefore the duration of the current exper-iment was extended to 48 h to better capture the temporal pattern ofsodium excretion and any shifts in the set points of the regulatory systemcontrolling thirst. The total amount of feed and water offered was weighedand recorded on the first day, after 24 h the refusals were then weighedand recorded and amount consumed was calculated as the difference, thiswas then repeated for the second day.
Blood samples (9 ml) were taken using indwelling jugular cathetersand collected in EDTA vacutainers at 0, 2, 4, 8, 20, 24, 28, 32, 44 and 48 hfor hormone analysis (AVP, aldosterone, leptin and insulin). Blood sam-ples were immediately centrifuged after collection at 1106 × g for 15 min,and the plasma was split across 3 Eppendorf tubes and stored at −20 ◦Cuntil analysis. Urine was collected in a container below each metabolismpen at the same intervals as above to determine daily urinary outputand 10 ml samples were frozen for later analysis of sodium concentrationby inductively coupled plasma atomic emission spectrometry (Dahlquistand Knoll, 1978) using a Spectro CIROS ICPAES machine (Waite AnalyticalServices, The University of Adelaide). Samples were digested with nitricacid and finished with hydrochloric acid as described by McQuaker et al.(1979). The intra-assay coefficient of variation for sodium concentrationwas 2.88%.
2.2. Hormone assays
Concentration of arginine vasopressin (AVP) in the plasma was mea-sured using a double-antibody radioimmunoassay as described by Digbyet al. (2008). The assay included 6 replicates of 3 control samples con-taining 9.2, 24.5 and 80.8 pg/ml, which were used to estimate intra-assaycoefficients of variation of 6.1%, 4.6% and 4.1% and inter-assay coefficientsof variation of 6.2%, 4.6% and 4.2%.
Concentration of aldosterone in plasma was measured using a modi-fied radioimmunoassay described previously by James and Wilson (1976)and validated by Digby et al. (2008). The assay included 6 replicates of 3control samples containing 95.2, 145.3 and 380.2 pg/ml, which were usedto estimate intra-assay coefficients of variation of 6.1%, 7.0% and 6.7% andinter-assay coefficients of variation of 5.6%, 3.9% and 5.2%.
S.N. Digby et al. / Small Ruminant Research 91 (2010) 87–92 89
Table 1Total saline water intake, urinary output, sodium excretion, daily mean plasma aldosterone, total feed intake and daily plasma insulin production (areaunder the curve – AUC) in lambs born from mothers fed high salt during gestation (S-lambs) or fed a low salt diet (C-lambs) on each day (day 1; day 2, righthand side) or as a total over the 2 days (left hand side). Values are means ± SE.
C-lambs S-lambs P value Total day 1 + 2
Day 1 Day 2 Day 1 Day 2 Origin Time O × T C-lambs S-lambs P value
Plasma leptin was measured in duplicate by a double-antibodyadioimmunoassay (Blache et al., 2000). All samples were processed in aingle assay and the limit of detection was 0.06 ng/ml. The assay includedreplicates of 3 control samples containing 0.43, 0.98 and 1.68 ng/ml,hich were used to estimate the intra-assay coefficients of variation of
.1%, 6.0% and 6.5%.Plasma insulin was assayed in duplicate by a double-antibody
adioimmunoassay (Tindal et al., 1978) that had been validated for sheeplasma in our laboratory (Miller et al., 1995). All samples were processed
n a single assay and the limit of detection was 0.78 �U/ml. Six replicatesf 3 control samples containing 2.45, 3.63 and 8.70 �U/ml were includedn the assay and were used to estimate the intra-assay coefficients ofariation of 7.5%, 2.2% and 3.5%.
.3. Data analysis
For all hormones, on each day, the area under the curve was calculatedy interpolation using the trapezoidal rule at the time points 2, 4, 8, 20nd 24 h for day 1 and point 28, 32, 44 and 48 h for day 2 to illustrate theffect of salt ingestion on the activity of each hormonal system. The dailyormonal profiles are not presented for simplicity because there was noariation in hormone concentrations within each day. Plasma AVP con-entrations, urinary output, water intake and feed intake required squareoot transformation, sodium excretion was transformed to the power of.25 and plasma aldosterone concentrations required log transformationo meet the assumptions of the model. All parameters were analysed usingMANOVA procedure with fetal origin as the independent factor and withay as a repeated measure. Total water intake, urinary output and saltxcretion were calculated over the 2 days and analysed using ANOVA withetal origin as the independent factor. Data presented in tables and figuresre untransformed values, even though the statistical analysis may haveequired transformation as described above. The data was analysed usinghe statistical package JMP 7.0 (SAS Institute, Cary, NC, USA). All valuesresented are means ± standard error of the mean.
. Results
.1. Water intake, urinary output and sodium excretion
There was a significant interaction between fetal ori-in of the lambs (i.e. between C and S-lambs) and timeday 1 and 2) for saline water intake (P = 0.055; Table 1),rinary output (P = 0.002; Table 1), and sodium excretion
P = 0.002; Table 1). The C-lambs did not alter their salineater intake over the 2 days (P = 0.57), but during day 1,
-lambs consumed on average 1.8 l less than C-lambs andhen drank 1.5 l more on day 2 (P < 0.02; Table 1). Thisattern was reflected in urinary output where C-lambs uri-
nated a similar amount on each day (P = 0.28), but S-lambsurinated 800 ml less than C-lambs on day 1 and 4.1 l morethan C-lambs on day 2 (P = 0.007). The C-lambs excreted51–56 g of sodium each day, but S-lambs increased theirsodium excretion from 52 ± 6 g on day 1 to 72 ± 8 g on day2 (P = 0.004; Table 1). There was no effect of origin or day,nor an interaction between day and origin, on cumulativetotal water intake (P = 0.93; Table 1), total urinary out-put (P = 0.41; Table 1) or total sodium excretion (P = 0.31;Table 1) over the 2 days of consuming saline water.
3.2. Feed intake
There was no interaction between fetal origin of thelambs and time (day 1 and 2) on feed intake, but there wasa main effect of fetal origin (P = 0.02; Table 1). Over the 2days, S-lambs consumed approximately 0.5 kg DM/day lessthan C-lambs (35%, P = 0.02; Table 1).
3.3. RAS hormones, AVP and aldosterone
There was an effect of fetal origin of the lambs andtime (day 1 and 2) and their interaction on the area underthe curve (AUC) for plasma concentration of aldosterone(P = 0.02; Table 1, Fig. 1). The AUC for plasma concentra-tions of aldosterone on days 1 and 2 ranged from 167 to196 pg/ml for C-lambs (P = 0.522; Fig. 1) whilst the AUCfor plasma concentrations of aldosterone decreased bytwo-thirds from day 1 to 2 in S-lambs, from 214 ± 24 to74 ± 8 pg/ml (P = 0.0002; Fig. 1). The AVP concentrationwas highly variable between individuals within groups(coefficient variation within different time points; S-lambs,18–42%; C-lambs, 15–43%) and there were no effects offetal origin of the lambs, time (day 1 or 2), or their interac-tion on the AUC for plasma concentrations of AVP (P = 0.19).
3.4. Metabolic hormones, leptin and insulin
There was an effect of fetal origin of the lambs andtime (day 1 and 2), but no interaction, on the AUC forinsulin concentration (P = 0.03). On both days, insulin con-centration was approximately 20% lower in S-lambs than
salt retention that induced a thirst response which, in turn,
Fig. 1. Plasma concentrations of aldosterone for lambs born to ewes feda high salt diet (S-lambs – closed circles) or a control diet during preg-nancy (C-lambs – open circles), receiving an oral dose of salt at time 0(mean ± SEM).
C-lambs (Table 1). The AUC for plasma insulin concen-trations decreased by approximately 30% from day 1 to2 for both C-lambs (decrease of 62.5 ± 17 �U/ml) and S-lambs (decrease of 60.1 ± 16 �U/ml). There were no effectsof fetal origin of the lambs, time (day 1 or 2; C-lambs,day 1; 23.1 ± 1.9 ng/ml, day 2; 23.7 ± 1.8: S-lambs, day 1;22.0 ± 1.5 ng/ml, day 2; 18.7 ± 1.5 ng/ml), or their interac-tion on the AUC for leptin concentration (P = 0.18).
4. Discussion
This study is the first investigating the effect of fetal pro-gramming in sheep on voluntary intake of saline water andthe associated physiological changes such as feed intakeand hormonal balance controlling energy metabolism andsalt and water balance. Exposure to salt during fetal lifeaffected the physiological responses of lambs to a volun-tary intake of saline water during 48 h. Our results do notfully support our first hypotheses because the majority ofthe physiological parameters that differed between ‘salt-programmed lambs’ (S-lambs) and control lambs changedbetween the first and second days of saline water intake.This temporal variation and the effect of fetal program-ming were very strong for water intake, urinary output,sodium excretion and aldosterone secretion and illustratesthat fetal programming changed the capacity of lamb toadapt to salt load challenge. Our results support the secondhypothesis that the different mechanisms by which ‘salt-programmed offspring’ deal with excessive salt ingestionwill lead to a lower feed intake compared to their controlcounterparts. The reduction in feed intake was associatedwith a decrease in insulin secretion, which suggests a link
between the hormonal systems controlling osmolarity andthose controlling metabolism.
Fetal programming of lambs through salt exposure oftheir mothers during pregnancy seems to have altered
esearch 91 (2010) 87–92
the thirst threshold, as evidenced by lower water intakein S-lambs than in C-lambs (day 1), a finding consistentwith that of Digby et al. (2009) who administered pro-grammed and control lambs with a one-off oral salt load.However, in the present study, we have shown that afterthis initially lower intake of saline water, there was adegree of correction on the second day such that totalwater intake did not differ over the 2 days (C-lambs,22.9 ± 2.7 l; S-lambs, 22.6 ± 3.1 l; P = 0.9). This indicates that‘salt-programming’ of offspring is more likely to affect thetemporal dynamic of water intake following ingested saltrather than the longer-term (or basal) responses. It wouldbe important to confirm this conclusion with a longer-termstudy.
Perhaps even more noteworthy than the pattern ofwater intake is the temporal pattern of sodium excretionin urine. On day 1, salt excretion, urinary output and aldos-terone concentration were similar in S-lambs and C-lambs.But, by on day 2, urinary output and sodium excretionincreased, and aldosterone secretion decreased in S-lambs,whilst remaining unchanged in C-lambs. These results sup-port the conclusion that ‘salt-programmed offspring’ havealtered adaptive response to the constant ingestion ofsaline water. These responses to saline drinking water seemto differ from those that occur in response to a single oralbolus of salt as described by Digby et al. (2009). In thecurrent study, aldosterone secretion was lower in S-lambsthan in C-lambs, with a drop to less than 80 pg/ml in day2. This is opposite to the blunted response in aldosteronesecretion (i.e., a smaller decrease in aldosterone concentra-tion) in ‘salt-programmed offspring’ administered a singleoral salt challenge (Digby et al., 2009). Sodium reabsorptionin the kidney is controlled by aldosterone concentrations(Granger, 1998) and thus the lower aldosterone secretionin S-lambs on day 2 resulted in more sodium being excretedon this day in these animals. It seems that the initial (day 1)response of S-lambs to the provision of salty drinking waterwas to reduce water intake but, by day 2, the intake of saltywater increased by 40% when salt excretory mechanismsincreased by the same degree.
Our results showed that S-lambs voluntarily consumedabout 35% less feed than C-lambs during the 2 days ofdrinking saline drinking water. This could be due to theS-lambs having increased retention of salt in the first 24 hand changes in the renin–angiotensin system on the secondday, as suggested above. Another possibility is that S andC-lambs differed in their osmolarity of body fluids whichthen influenced feeding behaviour through changes in theactivity of the renin–angiotensin system (Baile and Della-Fera, 1981). In sheep, continuous intracerebroventricular(ICV) infusion of angiotensin II, a hormone controllingaldosterone secretion, over a period of about 4 days pro-duced thirst sensations and resulted in excessive waterintake (an increase of nearly three-fold) that caused rumi-nal distension and significantly reduced feed intake by 25%(Sunagawa et al., 2001). That is, angiotensin II increased
resulted in an increase in water intake and a decrease infeed intake. Our results cannot be explained by this cas-cade of events. During day 2 in S-lambs, the increase inthe intake of saline water was concomitant to a decrease
n aldosterone secretion suggesting a modification in theegulation of the renin–angiotensin system.
The decrease in secretion of insulin in both S and C-ambs between day 1 and 2 in response to drinking saline
ater suggest that the energy balance of the lambs, defineds the difference between energy expenditure and the sumf energy intake and energy reserves, has drifted towardsnegative value because of the decrease in feed intake
Blache et al., 2007). The decrease in insulin secretion isot consistent with previous results showing that insulinoncentrations were not affected by a one-off ingestion ofalt (Digby et al., 2009) but are similar to the results ofong-term feeding of sheep with high salt diet (Blache et al.,007). Moreover, in humans, plasma insulin decreased byp to 47% in response to an increase in salt intake, via saline
nfusion or consumption of salt in diet, however the mech-nisms responsible are not known (Goodfriend et al., 1991).he decrease in insulin secretion was greater in the S-lambshan in the C-lambs possibly because the S-lambs havelower feed intake than the C-lambs. However, previous
tudies in wethers have shown that the decrease in insulinollowing ingestion of high salt diet was independent of aecrease in intake (Blache et al., 2007). Alternatively, theetal programming of S-lambs by exposure of their preg-ant dams to high dietary salt could have changed theensitivity of the pancreas to salt intake or the level ofnergy expenditure of those lambs; however, no other datare available to support this hypothesis. Finally, it is alsoossible that the lower insulin in S-lambs could be due todifference in energy reserves, the third component of thenergy balance, or the rate of mobilisation of energy reserveChilliard et al., 2005). Both S-lambs and C-lambs had sim-lar leptin concentrations on day 1 but, on day 2, leptin wasower in S-lambs than in C-lambs, although not significant.his is similar to results from previous studies which havehown that leptin is not affected by fetal programming oralt ingestion (Blache et al., 2007; Digby et al., 2008, 2009).
In conclusion, exposure of pregnant ewes to high saltffects the physiological responses of their offspring to theonsumption of saline drinking water over a period of 2ays. The main differences are reflected in the temporalatterns of change in water intake, sodium excretion andldosterone concentration following the consumption ofaline drinking water. Importantly, these programmed dif-erences appear to lead to a marked reduction in voluntaryeed intake, thereby suggesting profound effects on animalerformance. The difference in the temporal pattern of thebove physiological responses suggested that thresholdshat control the cascade of responses – drinking in responseo salt intake, excretion of salt, secretion of aldosterone –
ight have been programmed at different levels betweenhe S-lambs and the C-lambs. The capacity of the pro-rammed lambs to deal with salt insult throughout alteredhresholds could be further explored by exposing them toalty water for period greater than 2 days.
cknowledgements
This work was supported by an Australian Postgradu-te Award, CSIRO Livestock Industries, and Future Farmndustries (formerly CRC for Plant-based Management of
esearch 91 (2010) 87–92 91
Dryland Salinity). We thank Margaret Blackberry (The Uni-versity of Western Australia) for the hormone analysis.
References
Baile, C.A., Della-Fera, M.A., 1981. Nature of hunger and satiety controlsystems in ruminants. J. Dairy Sci. 64, 1140–1152.
Blache, D., Tellam, R.L., Chagas, L.M., Blackberry, M.A., Vercoe, P.E., Martin,G.B., 2000. Level of nutrition affects leptin concentrations in plasmaand cerebrospinal fluid in sheep. J. Endocrinol. 165, 625–637.
Blache, D., Grandison, M.J., Masters, D.G., Dynes, R.A., Blackberry, M.A.,Martin, G.A., 2007. Relationships between metabolic endocrine sys-tems and voluntary feed intake in Merino sheep fed a high salt diet.Aust. J. Exp. Agric. 47, 544–550.
Blair-West, J.R., Brook, A.H., 1969. Circulatory changes and renin secretionin sheep in response to feeding. J. Physiol. 204, 15–30.
Cassis, L., Helton, M., English, V., Burke, G., 2002. Angiotensin II regulatesoxygen consumption. Am. J. Physiol. Regul. Integr. Comp. Physiol. 282,R445–R453.
Chadwick, M.A., Vercoe, P.E., Williams, I.H., Revell, D.K., 2009. Dietaryexposure of pregnant ewes to salt dictates how their offspring respondto salt as adults. Physiol. Behav. 97, 437–445.
Chilliard, Y., Delavaud, C., Bonnet, M., 2005. Leptin expression in rumi-nants: nutritional and physiological regulations in relation withenergy metabolism. Domest. Anim. Endocrinol. 29, 3–22.
Dahlquist, R.L., Knoll, J.W., 1978. Inductively coupled plasma-atomic emis-sion spectrometry: analysis of biological material and soils for major,trace and ultra-trace elements. Appl. Spectrosc. 32, 1–29.
Digby, S.N., Masters, D.G., Blache, D., Blackberry, M.A., Hynd, P.I., Revell,D.K., 2008. Reproductive capacity of Merino ewes fed a high-salt diet.Animal 2, 1353–1360.
Digby, S.N., Masters, D.G., Blache, D., Hynd, P.I., Revell, D.K., 2009. Offspringborn to ewes fed high salt during pregnancy have altered responsesto oral salt loads. Animal, doi:10.1017/S1751731109990772.
Granger, J.P., 1998. Regulation of extracellular fluid volume by integratedcontrol of sodium excretion. Adv. Physiol. Educ. 275, 157–168.
James, V.H.T., Wilson, G.A., 1976. Determination of aldosterone in biologi-cal fluids. In: Reid, E. (Ed.), Assay of Drugs and Other Trace Compoundsin Biological Fluids. Elsevier Publishing, Amsterdam, pp. 149–158.
Masters, D.G., Rintoul, A.J., Dynes, R.A., Pearce, K.L., Norman, H.C., 2005.Feed intake and production in sheep fed diets high in sodium andpotassium. Aust. J. Agric. Res. 56, 427–434.
Masters, D.G., Edwards, N., Sillence, M., Avery, A., Revell, D., Friend, M.,Sanford, P., Saul, G., Beverly, C., Young, J., 2006. The role of livestock inthe management of dryland salinity. Aust. J. Exp. Agric. 46, 733–741.
Masters, D.G., Benes, S.E., Norman, H.C., 2007. Biosaline agriculture for for-age and livestock production. Agric. Ecosyst. Environ. 119, 234–248.
McQuaker, N.R., Brown, D.F., Kluckner, P.D., 1979. Digestion of environ-mental materials for analysis by inductively coupled plasma-atomicemission spectrometry. Anal. Chem. 51, 1082–1084.
Miller, D.W., Blache, D., Martin, G.B., 1995. The role of intracerebral insulinin the effect of nutrition on gonadotrophin secretion in mature malesheep. J. Endocrinol. 147, 321–329.
Peirce, A.W., 1957. Studies on salt tolerance of sheep. I. The tolerance ofsheep for sodium chloride in the drinking water. Aust. J. Agric. Res. 8,711–722.
Potter, B.J., 1961. The renal response of sheep to prolonged ingestion ofsodium chloride. Aust. J. Agric. Res. 12, 440–445.
Potter, B.J., 1963. The effect of saline water on kidney tubular function andelectrolyte excretion in sheep. Aust. J. Agric. Res. 14, 518–528.
Potter, B.J., 1968. The influence of previous salt ingestion on the renal func-tion of sheep subjected to intravenous hypertonic saline. J. Physiol.194, 435–455.
Sunagawa, K., Weisinger, R.S., McKinley, M.J., Purcell, B.S., Thomson, C.,Burns, P.L., 2001. The role of angiotensin II in the central regulation offeed intake in sheep. Can. J. Anim. Sci. 81, 215–221.
Sunagawa, K., Hashimoto, T., Izuno, M., Hashizume, N., Okano, I.,Nagamine, I., Hirata, T., 2008. An intravenous replenishment of sali-vary components and dry forage intake in freely drinking large-type
goats. Asian-Aust. J. Anim. Sci. 21, 538–546.
Tindal, J.S., Knaggs, G.S., Hart, I.C., Blake, L.A., 1978. Release of growth hor-mone in lactating and non-lactating goats in relation to behaviour,stages of sleep, electroencephalograms, environmental stimuli andlevels of prolactin, insulin, glucose and free fatty acids in the circula-tion. J. Endocrinol. 76, 333–346.
Wilson, A.D., 1975. Influence of water salinity on sheep performance while
92 S.N. Digby et al. / Small Ru
Utley, P.R., Bradley, N.W., Boling, J.A., 1970. Effect of restricted water
intake on feed intake, nutrient digestibility and nitrogen metabolismin steers. J. Anim. Sci. 31, 130–135.
Wilson, A.D., 1966a. The value of Atriplex (saltbush) and Kochia (bluebush)species as food for sheep. Aust. J. Agric. Res. 17, 147–153.
Wilson, A.D., 1966b. The tolerance of sheep to sodium chloride in food ordrinking water. Aust. J. Agric. Res. 17, 503–514.
esearch 91 (2010) 87–92
grazing on natural grassland and saltbush pastures. Aust. J. Exp. Agric.Anim. Husb. 15, 760–765.
Wilson, A.D., Hindley, N.L., 1968. Effect of restricted access to water onthe intake of salty foods by Merino and Border Leicester sheep. Aust.J. Agric. Res. 19, 597–604.
