Volume 95, Issue 1 e14007

RESEARCH ARTICLE

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Adaptation mechanism of Phan Rang sheep to salinity in drinking water under tropical conditions

Thiet Nguyen,

Thiet Nguyen

orcid.org/0000-0002-8906-358X

Department of Agricultural Technology, College of Rural Development, Can Tho University, Can Tho, Vietnam

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Dat Nguyen Thanh,

Dat Nguyen Thanh

Department of Agricultural Technology, College of Rural Development, Can Tho University, Can Tho, Vietnam

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Ngu Nguyen Trong,

Ngu Nguyen Trong

orcid.org/0000-0003-2197-451X

Department of Animal Science, College of Agriculture, Can Tho University, Can Tho, Vietnam

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Narongsak Chaiyabutr,

Narongsak Chaiyabutr

orcid.org/0000-0002-3207-0885

Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

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Sumpun Thammacharoen,

Corresponding Author

Sumpun Thammacharoen

[email protected]

orcid.org/0000-0002-5500-1639

Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

Correspondence

Sumpun Thammacharoen, Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, HenriDunang street, Bangkok 10330, Thailand.

Email: [email protected]

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Thiet Nguyen,

Thiet Nguyen

orcid.org/0000-0002-8906-358X

Department of Agricultural Technology, College of Rural Development, Can Tho University, Can Tho, Vietnam

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Dat Nguyen Thanh,

Dat Nguyen Thanh

Department of Agricultural Technology, College of Rural Development, Can Tho University, Can Tho, Vietnam

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Ngu Nguyen Trong,

Ngu Nguyen Trong

orcid.org/0000-0003-2197-451X

Department of Animal Science, College of Agriculture, Can Tho University, Can Tho, Vietnam

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Narongsak Chaiyabutr,

Narongsak Chaiyabutr

orcid.org/0000-0002-3207-0885

Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

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Sumpun Thammacharoen,

Corresponding Author

Sumpun Thammacharoen

[email protected]

orcid.org/0000-0002-5500-1639

Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

Correspondence

Sumpun Thammacharoen, Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, HenriDunang street, Bangkok 10330, Thailand.

Email: [email protected]

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First published: 08 October 2024

https://doi.org/10.1111/asj.14007

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Abstract

The aims of this study were to determine adaptation mechanism of sheep to salinity in drinking water. A group of 10 male sheep were used in a 6-week of experiment, with 1 week for pre-treatment period (Week 1), 4 weeks for during treatment period (Week 2 to Week 5), and 1 week for posttreatment period (Week 6). During the pre- and posttreatment periods, sheep consumed with fresh water. However, during treatment period, they were given with diluted seawater (DSW) at concentrations of 0.5%, 1.0%, 1.5%, and 2% for Weeks 2, 3, 4, and 5, respectively. Animal was offered 300 g concentrate and corn stover silage for ab libitum. Dry matter intake decreased as DSW increased, whereas sheep drinking DSW showed an increase in water intake and urine volume (p < 0.05). Body weight change decreased in 2% DSW. Sheep consuming 2% DSW exhibited higher plasma electrolyte levels compared to other groups. But plasma levels of AST, ALT, and creatinine were unaffected by DSW (p > 0.05). The elevated levels and excretions of urinary electrolytes were found in DSW groups (p < 0.05). Water balance was unaffected by DSW, except during the recovery period. It concluded that adapted sheep can consume DSW up to 1.5% without harmful effects.

1 INTRODUCTION

Livestock farming plays a vital role in global agricultural economies, providing essential resources like meat and milk, as well as income and livelihoods for millions. However, the sustainability of livestock production faces increasing threats from environmental stressors such as salinity in water sources and high temperatures. Previous studies indicated that sheep drinking with saline water up to 8.3 g/L did not affect dry matter intake (DMI) but decreased DMI at salt level of 15 g/L (Moura et al., 2016; Yousfi & Salem, 2017). Additionally, adapted goats have shown tolerance to 1.5% or 2% saline water without adverse productivity (Nguyen et al., 2024; Zoidis & Hadjigeorgiou, 2018). This adaptation is attributed to two main factors: Firstly, low concentration of saline water stimulated to drink more water, while high concentration of saline water they rejected to drink water, even when salt deprived (Chandrashekar et al., 2010); secondly, their kidney's ability excreted excess salt and maintain fluid balance (Assad & El-Sherif, 2002; Nguyen, Truong, et al., 2022). In short, the livestock species confronting these challenges are goat and sheep, breeds renowned for its resilience and adaptability, particularly in the face of adverse environmental conditions (Silanikove, 2000). Phan Rang sheep, predominantly raised in central provinces of Vietnam, often faced with lack of freshwater or high levels of salinity in their drinking water during dry season due to saline intrusion in freshwater sources. Despite this environmental constraint, Phan Rang sheep exhibit remarkable adaptability, continuing to thrive in these challenging conditions. Understanding the mechanisms underlying their adaptation to salinity in drinking water is crucial for effective management strategies of small ruminant in the areas with lack of freshwater or high content of salt water (Digby et al., 2011). Wilson (1975) observed that sheep consuming saline water at levels below 1.2% experienced no change in body weight (BW). However, when the saline water concentration increased from 1.2% to 2%, a decrease in BW was noted. Until now in Vietnam, there is no information to evaluate the adaptation mechanism of Phan Rang sheep to salinity in drinking water under tropical conditions. In addition, our study has demonstrated that stepwise adaption to diluted seawater (DSW) with a level of 1.5% for 21 days has no impacts on productivity of goats (Nguyen et al., 2024). Therefore, we would like to apply our recommendation in goats to investigate in sheep and extent to impacts of DSW up to 2%. The aims of this study were to determine how varying levels of DSW affects the adaptation of Phan Rang sheep under tropical conditions. The hypothesis of the present experiment is whether the 7-day adaptive for each concentration increased in diluted saline water influence intakes of feed and water, body weight change, and biochemical blood parameters in sheep.

2 MATERIALS AND METHODS

2.1 The location of study

The experiment was approved by the Scientific Committee of Can Tho University (#3559). The experiment was conducted at Experimental farm, College of Rural Development, Can Tho University during the hot season.

2.2 Climate conditions during the experimental period

Table 1 showed the climate conditions throughout the experiment. The average ambient temperature (Ta) and temperature and humidity index (THI) during the experimental period were low at 09:00 h (from 29.50 to 31.25°C for Ta and from 76.69 to 80.39 for THI) and high at 13:00 and 15:00 h (33.5 to 35.5°C for Ta and 79.80 and 82.13 for THI). However, the relative humidity percentages were high at 09:00 h (from 41.5 to 51.5%) and low at 13:00 and 15:00 h (24.5%–32.5%) in this study (Table 1).

TABLE 1. Climate conditions in the experimental periods.

Climate conditions	Weeks	09:00	11:00	13:00	15:00
Ambient temperature (°C)	WK1	29.50 ± 0.50	31.50 ± 0.50	33.50 ± 1.5	34.25 ± 0.25
	WK2	29.50 ± 0.50	32.25 ± 0.25	33.50 ± 0.50	34.25 ± 0.25
	WK3	30.50 ± 0.50	32.25 ± 0.25	34.25 ± 0.25	34.50 ± 0.50
	WK4	30.25 ± 0.25	32.50 ± 0.50	34.25 ± 0.25	34.50 ± 0.25
	WK5	31.25 ± 0.25	33.50 ± 0.50	35.50 ± 0.50	35.25 ± 0.25
	WK6	31.25 ± 0.25	33.25 ± 0.25	35.50 ± 0.50	35.00 ± 1.00
Relative humidity (%)	WK1	56.50 ± 1.50	40.00 ± 1.00	32.00 ± 2.00	29.00 ± 2.00
	WK2	47.50 ± 2.50	36.00 ± 1.00	28.50 ± 1.50	28.25 ± 0.25
	WK3	41.50 ± 1.50	33.50 ± 0.50	29.50 ± 0.50	24.50 ± 0.50
	WK4	41.50 ± 1.50	36.00 ± 1.00	28.00 ± 1.00	26.25 ± 0.25
	WK5	46.50 ± 0.50	39.00 ± 1.00	32.00 ± 1.00	29.00 ± 1.00
	WK6	51.50 ± 0.50	38.50 ± 0.50	32.50 ± 0.50	31.50 ± 1.50
Temperature and humidity index (THI)	WK1	78.81 ± 0.90	78.84 ± 0.77	79.80 ± 2.06	80.05 ± 0.66
	WK2	77.49 ± 0.28	79.05 ± 0.12	79.12 ± 0.27	79.90 ± 0.32
	WK3	77.87 ± 0.84	78.62 ± 0.37	80.14 ± 0.18	79.44 ± 0.62
	WK4	77.56 ± 0.53	79.34 ± 0.41	79.85 ± 0.08	80.58 ± 0.22
	WK5	79.59 ± 0.40	81.06 ± 0.41	82.02 ± 0.36	81.14 ± 0.07
	WK6	80.39 ± 0.25	80.67 ± 0.21	82.13 ± 0.67	81.35 ± 0.82

2.3 Experimental design and management

A group of 10 male sheep, each weighing 21.20 ± 0.47 kg and aged 6 months, were used in a 6-week of experiment. The experiment included a 1-week for pre-treatment period (Week 1, WK1), a 4 weeks for during treatment period (from Week 2 to Week 5) and a 1-week for posttreatment period (Week 6, WK6). All sheep were kept in the metabolic cages (1.2 × 1 m) with plastic floor for 2 weeks of adaptation period. Throughout the pre- and posttreatment periods, the sheep were provided with fresh water. However, during treatment period, the sheep were consumed DSW with varying concentrations. This stepwise adaptation to saline water followed recommendations from previous studies conducted on goats (Nguyen et al., 2024; Zoidis & Hadjigeorgiou, 2018). Specifically, the sheep consumed DSW with concentrations of 0.5%; 1.0%; 1.5%, and 2% at Week 2 (WK2), Week 3 (WK3), Week 4 (WK4), and Week 5 (WK5), respectively. In this study, the DSW was prepared during the treatment period by diluting concentrated seawater (10%) with fresh water to achieve the desired concentrations (0.5%, 1.0%, 1.5%, and 2%) using the formula: C1V1 = C2V2, where C1 is the concentration of the initial solution, V1 is the volume of the initial solution, C2 is the concentration of the final solution, and V2 is the volume of the final solution. The DSW's concentration was verified using a refractometer (Master S28M; Atago, Japan). The chemical composition of water provided to the sheep in this experiment, which was presented in Table 2. All sheep received the same experimental diet, consisting of 300 g commercial concentrate (200 g for morning feeding and 100 g for afternoon feeding) and ad libitum corn stover silage for both morning and afternoon feedings. This feeding regime was typical for growing sheep on the farm. The chemical composition of concentrate and corn stover silage was presented in Table 3.

TABLE 2. Chemical composition of drinking water in the experiment.

Items	Fresh water	Diluted seawater
Items	Fresh water	0.5%	1.0%	1.5%	2.0%
TDS (g/L)	0,10	5.00	10.00	15.00	20.00
Cl⁺ (g/L)	0.028	3.26	6.7	10.2	14.21
K⁺ (g/L)	0.004	0.06	0.13	0.21	0.24
Na⁺ (g/L)	0.017	1.65	3.45	5.01	6.76
Ca²⁺ (g/L)	0.016	0.03	0.05	0.10	0.13
Mg²⁺ (g/L)	0.10	0.21	0.47	0.58	0.78

Abbreviations: Ca, calcium; Cl, chloride; K, potassium; Mg, magnesium; Na, sodium; TDS, total dissolved solids.

TABLE 3. Chemical composition of concentrate and corn stover silage in the experiment.

Items (%)	Concentrate	Corn stover silage
Dry matter	88.50	20.5
Crude protein	19.20	7.95
Neutral detergent fiber	39.36	65.18
Acid detergent fiber	20.25	46.91
Ash	8.06	9.67

2.4 Data collection and measurements

2.4.1 Data collection for climate conditions

The humidity and air temperature were recorded every week at 09:00, 11:00, 13:00, and 15:00 and then calculated THI.

2.4.2 Feed collection and measurements

Feed refusal was recorded daily at 07:00 h and at 08:00 and 14:00 h for feed offer throughout the experiment periods. Samples for both feed offer and refusal were collected and divided into two parts. The first part was dried in an oven at 105°C until a constant weight was achieved to determine dry matter content. The second part was stored in a freezer at −20°C for later analysis of chemical composition. Crude protein (CP) and ash content were determined using the method of AOAC (1990). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed according to the method described by Van Soest et al. (1991).

2.4.3 Water intake (WI) collection and measurements

WI was measured daily 07:00 h from the beginning to the end of the experiment. Then water was daily provided at 08:00 h and refill at 14:00 h. Water samples were analyzed for sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺) using atomic absorption spectrophotometry (Thermo iCE3000 series; Thermo Fisher Scientific, China). Chloride concentration was determined through titration using 0.02 N AgNO₃. Electrical conductivity (EC) was determined by EC meter (Schott Instruments D-55122, Mainz, Germany) and total dissolved solids (TDS) were calculated from EC using the formula: TDS = EC (mS/cm) × 0.454.

2.4.4 Water balance measurements

Water balance was different between total water input and water output. Total water input from this study consisted of water from trough (drinking water) and diet (corn stover silage and concentrate) by drying the sample in oven at 105°C and the weight loss of sample is water from diet. Total water output consisted of water from urine and feces. The ambient temperature and humidity in the housing were recorded twice per week throughout the experiment, specifically at 09:00, 11:00, 13:00, and 15:00 during the daytime. The TH was calculated as the recommendation of Thammacharoen et al. (2020).

2.4.5 Urinary and blood collection

On the last 2 days of each week, total collection for urine and feces was applied and recorded at 07:30 h after recording feed and water refusal from each sheep. Subsequently, 100 g samples of feces and urine were collected and stored in the freezer for later analysis. Additionally, on the last day of each week, blood samples were also collected at 10:00 h into heparin tubes (2 mL), kept in crushed ice, and then transported to the laboratory for centrifugation to harvest plasma for subsequent analysis. The concentration of plasma and urine electrolytes were measured using an automatic analyzer machine (ST200 PRO, Sensa Core, India). The electrolytes excretion (Uex) for sodium (UexNa), potassium (UexK), and chloride (UexCl) were calculated from levels of urine electrolytes and urine volume. Similarly, plasma urea, creatinine, AST, and ALT levels were also determined using an automatic analyzer machine (XL200; Erba Mannheim, Germany).

2.5 Statistical analysis

All data are presented as mean ± standard error of the mean (SEM). The data for DMI, WI, and urine volume were averagely calculated for every week and then analyzed by one-way ANOVA. The data for BW, body weight change, blood, and urinary parameters were analyzed by one-way ANOVA. Pairwise comparisons were conducted using Tukey's post hoc test. Significance was declared at p < 0.05, while a tendency was noted at 0.05 < p < 0.10.

The analysis of data was performed by a mixed linear model with treatment as the fixed effect and animal as random effect. The mixed model used in this study as following:

y=\upmu +{\mathrm{T}}_{\mathrm{i}}+{\mathrm{D}}_{\mathrm{j}}\ \left({\mathrm{T}}_{\mathrm{i}}\right)+{\mathrm{A}}_{\mathrm{k}}+{\mathrm{e}}_{\mathrm{i}\mathrm{jkl}}.

where y = dependent variable, μ = general mean, T_i = effect of treatment i, D_j (T_i) = effect of day in treatment (T_i), A_k = ramdom effect of animal, and e_ijkl = residual error.

3 RESULTS

3.1 Changes on BW, total DMI, WI, and urine volume

BW tended to increase from fresh water (0.0%, WK1) to 1.5% DSW (WK4) but decreased at 2% DSW (WK6), followed by recovery at WK6 (Table 4, p = 0.068). Sheep drinking 2% DSW had a detrimental effect on BW, resulting in a significantly lower BW change compared to other groups (Figure 1; p < 0.001). WI gradually increased throughout the experiment, although sheep were provided fresh water during the recovery period (WK6). But, DMI decreased as DSW concentration gradually increased and subsequently recovered during the posttreatment period when fresh water was offered again (p < 0.05). The urine volume was significantly higher during the DSW period compared to the pre-treatment period and remained high during the posttreatment period (p < 0.04, Table 4).

TABLE 4. Effects of diluted seawater on body weight, dry matter intake, water intake, and urine volume in sheep.

Items	Pre-treatment	During treatment				Posttreatment	SEM	p-Value
Items	WK1	WK2	WK3	WK4	WK5	WK6	SEM	p-Value
Body weight (BW, kg)	21.20	21.90	22.42	22.80	21.62	22.90	0.46	0.068
Dry matter intake (DMI, g/head/day)	550.24	551.48	546.94	553.67	517.26	559.32	8.90	0.10
DMI per kg BW (g/kgBW/day)	26.05^a	25.26^ab	24.47^ab	24.33^ab	24.02^b	24.49^ab	0,54	0.025
Water intake (WI, kg/head/day)	1.32^b	1.48^b	1.52^bc	1.65^ab	1.97^a	2.09^a	0.13	0.001
WI per kg BW (g/kgBW/day)	62.41^b	67.51^b	67.78^b	72.32^ab	90.76^a	90.87^a	5.16	0.001
Urine volume (kg/head/day)	0.62^b	0.77^ab	0.86^ab	0.97^ab	1.15^a	1.09^ab	0.13	0.04

^a,bValues with different superscripts within the same row indicate statistically significant differences (p < 0.05). Pre-treatment (WK1): sheep consumed fresh water at first week of experiment; during treatment from Week 2 to 6: WK2: sheep consumed diluted seawater with a concentration of 0.5% at second week of experiment; WK3: sheep consumed diluted seawater with a concentration of 1.0% at third week of experiment; WK4: sheep consumed diluted seawater with a concentration of 1.5% at fourth week of experiment; WK5: sheep consumed diluted seawater with a concentration of 2.0% at fifth week of experiment; posttreatment (WK6): sheep consumed fresh water at sixth week of experiment.
Abbreviations: BW, body weight; SEM, standard error of the mean.

Details are in the caption following the image — **FIGURE 1**
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Effects of diluted seawater on body weight change (kg/head/week) in sheep. Sheep consumed with diluted seawater at 0.5%, 1.0%, 1.5%, and 2% respectively (DSW0.5, DSW1.0, DSW1.5, and DSW2.0); sheep consumed with fresh water (post-FW). Body weight change in DSW0.5 was calculated from difference between WK2 and WK1; BW change in DSW1.0 was calculated from difference between WK3 and WK2; BW change in DSW1.5 was calculated from difference between WK4 and WK3; BW change in DSW2.0 was calculated from difference between WK5 and WK4; BW change in post-FW was calculated from difference between WK6 and WK5. ^{a, b, c:} Values with different superscripts within the same row indicate statistically significant differences (p < 0.05).

3.2 Changes on blood biochemical parameters, liver, and kidney functions

Concentrations of plasma electrolytes and calcium significantly increased during the treatment period as sheep consumed gradually increasing levels of DSW and then decreased when sheep consumed fresh water during the posttreatment period (p < 0.05, Table 5). In contrast, plasma urea concentration was lower in the DSW groups compared to the fresh water groups (p < 0.001). The levels of plasma AST, ALT, and creatinine remained unchanged throughout the experiment (p > 0.05).

TABLE 5. Effects of diluted seawater on blood biochemical parameters.

Items	Pre-treatment	During treatment				Posttreatment	SEM	p-Value
Items	WK1	WK2	WK3	WK4	WK5	WK6	SEM	p-Value
Na⁺ (mmol/L)	143.80^c	143.58^c	146.29^bc	147.09^b	150.19^a	145.34^bc	0.66	0.001
K⁺ (mmol/L)	4.21^b	4.54^ab	4.63^ab	4.59^ab	4.84^a	4.50^ab	0.13	0.04
Cl⁻ (mmol/L)	104.94^b	105.23^b	108.64^a	108.36^a	110.61^a	103.45^b	0.72	0.001
Ca²⁺ (mmol/L)	1.16^c	1.21^bc	1.20^bc	1.21^bc	1.31^a	1.24^ab	0.02	0.001
AST (U/L)	92.21	92.62	100.21	96.34	99.31	98.08	7.26	0.95
ALT (U/L)	14.76	15.49	14.13	12.99	14.34	15.23	0.93	0.47
Urea (mmol/L)	8.90^a	6.91^b	6.65^b	5.99^b	6.81^b	7.02^b	0.31	0.001
Creatinine (μmol/L)	77.65	80.99	76.54	78.28	77.19	74.74	2.56	0.66

^a,b,cValues with different superscripts within the same row indicate statistically significant differences (p < 0.05). Pre-treatment (WK1): sheep consumed fresh water at first week of experiment; during treatment from Week 2 to 6: WK2: sheep consumed diluted seawater with a concentration of 0.5% at second week of experiment; WK3: sheep consumed diluted seawater with a concentration of 1.0% at third week of experiment; WK4: sheep consumed diluted seawater with a concentration of 1.5% at fourth week of experiment; WK5: sheep consumed diluted seawater with a concentration of 2.0% at fifth week of experiment; posttreatment (WK6): sheep consumed fresh water at sixth week of experiment.
Abbreviation: SEM, standard error of the mean.

3.3 Changes on concentrations and excretions of urinary electrolytes in sheep

The concentrations of urinary sodium and chloride significantly increased as the level of DSW increased and then decreased when sheep were provided with fresh water during the posttreatment period (p < 0.001, Table 6). But urinary potassium levels did not differ whether sheep consumed fresh water or DSW. The urinary excretion of electrolytes was higher in the DSW groups compared to the fresh water groups (p < 0.05, Table 6).

TABLE 6. Effects of diluted seawater on concentrations (mmol/L) and excretions of urinary electrolytes (mmol/head/day) in sheep.

Items	Pre-treatment	During treatment				Posttreatment	SEM	p-Value
Items	WK1	WK2	WK3	WK4	WK5	WK6	SEM	p-Value
Na⁺	155.92^b	228.00^b	364.10^a	365.0^a	449.60^a	235.30^b	21.31	0.001
K⁺	167.20	143.30	170.40	126.80	186.0	127.30	16.61	0.07
Cl⁺	244.7^c	485.2^b	516.8^ab	574.1^a	603.3^a	217.5^c	25.74	0.001
UexNa	99.02^c	176.56^bc	312.65^b	344.67^ab	538.62^a	257.17^bc	50.53	0.001
UexK	109.33^b	105.82^b	138.42^ab	132.59^ab	208.15^a	137.86^ab	24.06	0.05
UexCl	152.63^d	367.67^b	442.71^bc	551.85^ac	688.10^a	226.42^bd	55.88	0.001

^a,b,c,dValues with different superscripts within the same row indicate statistically significant differences (p < 0.05). Pre-treatment (WK1): sheep consumed fresh water at first week of experiment; During treatment from Week 2 to 6: WK2: sheep consumed diluted seawater with a concentration of 0.5% at second week of experiment; WK3: sheep consumed diluted seawater with a concentration of 1.0% at third week of experiment; WK4: sheep consumed diluted seawater with a concentration of 1.5% at fourth week of experiment; WK5: sheep consumed diluted seawater with a concentration of 2.0% at fifth week of experiment; posttreatment (WK6): sheep consumed fresh water at sixth week of experiment.
Abbreviations: SEM, standard error of the mean; UexCl, urinary excretion of chloride; UexK, urinary excretion of potassium; UexNa, urinary excretion of sodium.

3.4 Changes in water balance in sheep drinking with variation of DSW

Total water input was significantly increased by the varying levels of DSW (p < 0.01, Table 7). Although water from feed was higher in the fresh water groups than in the 2% DSW group in this study (p < 0.05, Table 7). In contrast, total water output remained similar throughout the experiment weeks. Although, higher urinary excretion in animals consuming DSW compared to those consuming fresh water, they saved the water from the feces, resulting in drier feces (p < 0.05, Table 7).

TABLE 7. Effects of diluted seawater on water balance in sheep.

Items	Pre-treatment	During treatment				Posttreatment	SEM	p-Value
Items	WK1	WK2	WK3	WK4	WK5	WK6	SEM	p-Value
Water from container (kg/head/day)	1.32^b	1.48^b	1.52^bc	1.65^ab	1.97^ac	2.09^a	0.13	0.001
Water from feed (kg/head/day)	0.88^ab	0.89^ab	0.87^ab	0.89^ab	0.75^b	0.92^a	0.04	0.03
Total water input (kg/head/day)	2.21^b	2.36^b	2.39^b	2.54^ab	2.72^ab	3.01^a	0.14	0.01
Water from feces (kg/head/day)	0.33^a	0.26^ab	0.265^ab	0.25^ab	0.21^b	0.28^ab	0.02	0.04
Water from urine (kg/head/day)	0.62^b	0.77^ab	0.86^ab	0.97^ab	1.15^a	1.09^ab	0.13	0.04
Total water output (kg/head/day)	0.94	1.06	1.13	1.22	1.37	1.40	0.13	0.14
Water balance (kg/head/day)	1.27^b	1.31^b	1.26^b	1.32^b	1.35^ab	1.62^a	0.07	0.01

^a,b,cValues with different superscripts within the same row indicate statistically significant differences (p < 0.05). Pre-treatment (WK1): sheep consumed fresh water at first week of experiment; during treatment from Week 2 to 6: WK2: sheep consumed diluted seawater with a concentration of 0.5% at second week of experiment; WK3: sheep consumed diluted seawater with a concentration of 1.0% at third week of experiment; WK4: sheep consumed diluted seawater with a concentration of 1.5% at fourth week of experiment; WK5: sheep consumed diluted seawater with a concentration of 2.0% at fifth week of experiment; posttreatment (WK6): sheep consumed fresh water at sixth week of experiment.
Abbreviation: SEM, standard error of the mean.

4 DISCUSSION

This study further applies to our recommendation of previous study in goats to extend on sheep. The findings revealed that sheep consuming DSW up to 1.5% showed no impact on DMI, whereas at 2% DMI decreased. Phan Rang sheep exhibited a higher consumption of DSW compared to fresh water. Increasing salinity levels may affect electrolyte plasma concentrations and kidney electrolyte handling. However, there were no significant effects observed on plasma AST and ALT levels in sheep consuming DSW, except for plasma urea.

The environmental conditions in the experimental area were similar to the typical condition of the tropical region. Specifically, the average ambient temperature, relative humidity, and the THI between 13:00 and 15:00 h were recorded at 34.50°C, 28.50%, and 81.05, respectively. The lower DMI resulting from high DSW caused to decrease nutrient digestibility as reported by Nguyen, Nguyen, et al. (2022) or some sheep feel uncomfortable when drank with 2% DSW (more standing and panting) and then they stop eating the feed from the observation by this study. DMI was not affected by salt concentration at less than 1.0% in either sheep (Albuquerque et al., 2020; Araújo et al., 2019; Tulu et al., 2022) or goat (Tsukahara et al., 2016). Some studies have found that animals begin to decrease DMI when they consumed 1.5% saline water in sheep (Yousfi et al., 2016) and goat (Nguyen et al., 2024; Runa et al., 2019). Interestingly, goat can consume saline water up to 2% without the impacts on DMI if they were gradually adapted with saline water (Zoidis & Hadjigeorgiou, 2018), which differ the results of this study. However, it is worth noting that sheep in this study were also adapted to DSW weekly. Yousfi et al. (2016) found that Barbarine sheep drinking saline water with a concentration of 1.1%–1.5% had decreased DMI compared to those drinking tap water. Additionally, Abou Hussien et al. (1994) reported that sheep consuming water with 9.5 g TDS/L had decreased DMI, but this effect was not observed in goats. These results suggest that goats may have a better ability to tolerate salt compared to sheep. This was confirmed by previous studies that negative effects of saline water on performance and health varied based on species and breeds, adaptation, and environmental conditions (Nguyen et al., 2024; Nguyen & Thammacharoen, 2022; Yape Kii et al., 2005).

In response to elevated salt levels in their drinking water, Phan Rang sheep exhibited increased their WI. By drinking more water, they dilute the concentration of salts in their bodies or their kidneys adjusted to increase the rate of urine production and composition to maintain osmotic balance within the body (Abou Hussien et al., 1994; McGregor, 2004). Sheep drinking high saline water displayed two primary responses: heightened WI or decreased DMI as reported by previous studies (Digby et al., 2010; Noureddine et al., 2022). In addition, Phan Rang sheep demonstrated adaptations to minimize the salt stress by absorbing more water from feces and made it drier as compared to those drinking fresh water (Table 7). These observations were supported by findings in the previous studies (Assad & El-sherif, 2002; Nguyen, Nguyen, et al., 2022).

There was a decrease in body weight change when sheep consumed 2% DSW, but they regained their weight after drinking fresh water. Similarly, previous studies have indicated that saline water can negatively affect the performance of both goat (Nguyen, Truong, et al., 2022) and sheep (Hekal, 2015; Yousfi & Salem, 2017). The decrease in BW from effect of saline water may result from a decrease in DMI, leading to decrease in nutrition intake for the animals (Ghanem et al., 2018; Nguyen, Nguyen, et al., 2022; Nguyen, Truong, et al., 2022). But, adapted goats in the low climatic conditions could be tolerance with 2% saline water without the negative impacts on health status and productivity (Zoidis & Hadjigeorgiou, 2018). The varying responses to different levels of saline water may be influenced by species or climate conditions (low or high climate conditions). Some studies have found that if sheep drinking saline water with low concentration (less than 1%) did not effect on BW (Albuquerque et al., 2020; Araújo et al., 2019). Interestingly, the present study found that sheep adapted to DSW up to 1.5% had no impact on BW. This finding was consistent with the report by Nguyen et al. (2024) regarding adapted goats.

Sheep possess a remarkable ability to adapt to environmental changes, including variations in water quality and quantity and high ambient temperature. This adaptation may involve efficient kidney function to filter out excess salts and conserve water, as well as the regulation of ion transporters in the kidneys and other tissues. This study reveals that sheep drinking DSW exhibited increased concentrations of plasma electrolytes, leading to excrete more urinary mineral composition than those drinking fresh water. Macfarlane (1982) proposed that goats may be more adapted to higher salt loads than sheep, due to slightly better Na pumps. This hypothesis was supported by present findings in sheep and previous study in goats (Zoidis & Hadjigeorgiou, 2018), where adapted sheep showed lower tolerance to saline water than adapted goats (1.5% vs. 2.0%).

Saline water contains high levels of dissolved salts, which can affect the plasma electrolytes concentration in this study. Electrolytes such as sodium, potassium, chloride, and bicarbonate are crucial for various bodily functions including nerve conduction, muscle contraction, and maintaining fluid balance. Drinking water with high salt content can lead to an imbalance in these electrolytes, which can affect the sheep's overall health and physiological processes. This study suggested that plasma sodium, potassium, and chloride concentrations were the same with those drinking fresh water and stay in normal range (Jackson & Cockcroft, 2002) when sheep consumed DSW up to 1.5% but increased concentrations of plasma electrolytes at 2% DSW. The findings indicated that adapted sheep can maintain electrolyte levels at 1.5% DSW. Runa et al. (2022) noted that Boer goats drinking saline water showed an increase in plasma sodium and potassium concentrations, consistent with the findings of this study.

AST and ALT are enzymes primarily found in liver cells (hepatocytes), with small quantities present in other tissues. They are released into the bloodstream when there is damage to liver cells. Monitoring AST and ALT levels in the bloodstream is a common diagnostic tool used to assess liver health and function (Makawana et al., 2022). Elevated levels of these enzymes indicate liver damage or disease. Drinking saline water may not directly affect the activities of those enzymes. However, if saline water consumption leads to dehydration or electrolyte imbalances, it can indirectly impact liver function. Dehydration and electrolyte imbalances can stress the liver and affect its ability to function properly. This stress on the liver can result in increased release of AST and ALT levels into the bloodstream, leading to elevated enzyme activities. Additionally, severe dehydration or electrolyte disturbances can impair liver function directly, further elevating AST and ALT levels. But this study reveals that DSW had no effect on water balance (Table 7) or the elevated concentrations of plasma electrolyte in sheep consumed with 2% DSW only 7 days (short period), resulting unchanged plasma AST and ALT concentrations. In a research with 56 days of experiment, Nguyen et al. (2024) reported that non-adapted goats consuming DSW with a concentration of 1.5% exhibited an increase in AST and ALT levels compared to adapted goats. Similarly, earlier investigation found that an increase in plasma AST and ALT concentrations in sheep drinking saline water with a concentration below 1% compared to those consuming freshwater over a 9-month trial period (Ghanem et al., 2018). But Runa et al. (2020) reported that goats drinking high saline water showed no alterations in plasma AST and ALT concentrations.

Elevated levels of salt in the body can increase the workload on the kidneys. The kidneys filter waste products, including urea and creatinine from the blood. When the kidneys are stressed, they may not efficiently remove urea or creatinine, leading to higher blood urea and creatinine levels. This can be a sign of kidney dysfunction or dehydration. The findings from this study showed that sheep drinking fresh water exhibited an increase in plasma urea concentration compared to those drinking DSW. It means that there are no impacts of saline water on kidney function in this study. The higher in plasma urea level of sheep drinking fresh water may come from the higher protein intake due to higher DMI in the current experiment. Conversely, the lower plasma urea level in sheep consuming highly DSW may result from either increased urinary excretion or reduced protein intake due to lower DMI. This finding contrasted with a prior study by Zoidis and Hadjigeorgiou (2018), which observed that sheep drinking high saline water elevated plasma urea concentration. In contrast to urea level, plasma creatinine remained consistent throughout the experimental periods, consistent with findings in goats (Runa et al., 2020, 2022) and Barki sheep (Ghanem et al., 2018).

The results in this study indicated that the stepwise adaptation method has alleviated the negative impacts of DSW on health status and performance of sheep, even when consumed at levels of up to 1.5%. Additionally, it suggested that farmers could choose Phan Rang sheep for rearing in coastal areas of Vietnam affected by salinity intrusion during the hot season and may implement this stepwise adaptation accordingly.

ACKNOWLEDGMENTS

This research was funded by the National Foundation for Science and Technology Development (Nafosted), Vietnam, under grant number 106.05-2020.45.

CONFLICT OF INTEREST STATEMENT

The authors declare that there is no conflict of interests regarding the publication of this article.

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Volume95, Issue1

January/December 2024

e14007

Adaptation mechanism of Phan Rang sheep to salinity in drinking water under tropical conditions

Abstract

1 INTRODUCTION