Occurrence of higher levels of sodium and chloride

Some studies have shown that wells are the primary source of water containing elevated levels of salts. Koelkebeck et al. (Reference KOELKEBECK, MCKEE, HARRISON, PARSONS and ZIMMERMAN1999) found that sodium and chloride concentrations in rural well water were higher than those of the city water. Also, Abbas et al. (Reference ABBAS, ELZUBEIR and ARABBI2008a) have recently reported that levels of total dissolved solids, hardness, alkalinity, calcium, magnesium, chloride and sodium in rural well water in North Africa were higher compared to the Nile water (Table 1).

Table 1: Chemical analysis of water obtained from different sources.

(Source: Abbas et al., Reference ABBAS, ELZUBEIR and ARABBI2008a)

Effect of saline water on laying hens performance

Balnave and Zhang (Reference BALNAVE and ZHANG1993) found that, addition of 796 mg Na/l to the drinking water of laying hens negatively affect eggshell breaking strength, the concentration of calcium – binding protein (CaBP) and the activity of carbonic anhydrase (CA) when compared to the town water containing 10 mg Na/l. Moreng et al. (Reference MORENG, BALNAVE and ZHANG1992) confirmed these effects on eggshell by addition of 2 g NaCl/l to town water. Pourreza et al. (Reference POURREZA, NILI and EDRISS1994) studied the relationship of plasma calcium and phosphorus on the shell quality of laying hens receiving saline drinking water. The authors showed that offering higher level of NaCl either in the drinking water or in the feed to the laying hens decreased shell thickness and shell calcium, and increased the number of damaged eggs, but elevated level of NaCl in the drinking water was more deleterious to the eggshell.

The effects of saline drinking water on pullets at different ages were examined by Yoselewitz and Balnave (Reference YOSELEWITZ and BALNAVE1989b), who reported that when the birds were given saline drinking water (2g NaCl/l) before sexual maturity, their subsequent eggshell quality did not show any response to the saline water. The same effect was observed when laying hens receiving saline drinking water from or after point of lay. It was also noted that birds supplied with saline drinking water at 40-week-old produced eggs with defective shells more rapidly compared to those given saline drinking water during the first few weeks of lay. The effect of saline drinking water on eggshell quality can be overcome when hens in early lay were given town water (3 mM Na and <1mM Cl) for five weeks. This response was not observed with 40-week-old hens.

Zhang et al. (Reference ZHANG, MORENG and BALNAVE1991) reported that supplementing the drinking water of laying hens with 2g NaCl/l induced large increases in eggshell defects with significantly (two fold) higher incidence of embryonic deaths and a significantly lower (13%) hatchability of fertile eggs. Saline water had little effect on reproductive performance of cockerels. Yoselewitz and Balnave (Reference YOSELEWITZ and BALNAVE1989a) compared effects of sodium chloride when supplied to hens in the feed against supplementation with drinking water. The authors found that supplementing the drinking water of 50-week-old laying hens with NaCl at levels of 0.5, 1 and 2 g/l for seven weeks significantly increased eggshell defects two, three and four-fold respectively. Providing dietary NaCl at 1 or 2 g/kg in feed had little effect on eggshell quality.

Balnave et al. (Reference BALNAVE, YOSELEWITZ and DIXON1989) demonstrated the effect of NaCl in the drinking water (600 and 2000 mg NaCl/l) on the eggshell quality. The authors pointed out that there was a little effect of adding NaCl to the drinking water on blood acid – base balance and electrolytes, but significantly reduced carbon dioxide tension, and bicarbonate and calcium concentrations in the fluid surrounding the egg in the shell gland. Balnave and Yoselewitz (Reference BALNAVE and YOSELEWITZ1987) observed that shell defects due to saline drinking water (600 mg NaCl/L) declined when birds were placed on normal water for five weeks, but were still 1.4–2.1 fold greater than control values.

In contrast to the above reports, Maurice (Reference MAURICE1989) conducted four experiments with up to 90-week-old hens and provided up to 1200 ppm NaCl for as long as twelve weeks without causing any decrease in shell strength measured as shell weight per unit surface area. The author speculated that this contrasting result may have been due to breed differences.

A report by Pourreza and Edriss (1994) gave mixed results from high–level administration of NaCl through feed and water to White Leghorn hens. Eggshell thickness was reduced by 2000 ppm NaCl in drinking water, but not by 1000 ppm. The 2000 ppm level was also reported to increase the incidence of defective shells; however, that same water treatment coupled with an additional 2000 ppm NaCl in the feed did not elevate defective shell percentage above control levels. Damron (Reference DAMRON1998) results concurred with those reported by Maurice (Reference MAURICE1989), which were in contrast to other literature reports, as their visually determined shell defects and egg specific gravity measurements were not adversely affected by NaCl supplementation (tap water with 9 ppm Na supplemented with 0 to 800 ppm NaCl) of the drinking water supplied to the layers. Again, these authors speculated that results may have been due to the strain of bird employed. Chen and Balnave (Reference CHEN and BALNAVE2001) observed that production and eggshell quality were significantly reduced at 30ºC compared with 18ºC, but were not significantly affected by saline drinking water. The authors mentioned that these result indicated Isa Brown hens were relatively insensitive to intakes of NaCl from the drinking water at concentrations of 2 g/l. Researchers also suggested that, this contrasting sensitivity may relate to the concentration of dietary NaCl used during the selection of layer genotypes.

Potential mechanisms by which saline water affect eggshell quality

There have been some proposals put forward regarding the mechanism by which saline water affects eggshell quality. Austic and Keshavarz (Reference AUSTIC and KESHAVARZ1988) speculated that the eggshell defects observed when laying hens given excessive NaCl is due to the effect of salt on the eggshell calcification process, and this effect was exacerbated when dietary calcium is limiting. Balnave et al. (Reference BALNAVE, YOSELEWITZ and DIXON1989) suggested that the defect in eggshell quality as the result of providing saline water was mainly due to reduced supply of bicarbonate, rather than to an effect of Ca availability, in the lumen of the shell gland. The reduced residence time of eggs in the shell gland may also play a role in this problem.

Correction of eggshell defects caused by saline drinking water

There were some methods examined to overcome eggshell defect caused by saline water, such as replacement of saline water with town drinking water, resting hens from lay, addition of calcium carbonate to the diet and remove of NaCl from the diet. Recently simultaneous supplementation of saline drinking water with either sodium or ammonium bicarbonate was attempted which resulted in substantial reduction but not entire correction of occurrence of eggshell defect (Yoselewitz et al., Reference YOSELEWITZ, ZHANG and BALNAVE1991). Balnave and Zhang (Reference BALNAVE and ZHANG1993) provided saline drinking water containing dietary Zn sulphate, Zn–methionine or chelated Zn–EDTA (1 g/kg Zn), which resulted in significant reduction of the incidence of poor eggshell quality. Simultaneous supplementation of saline drinking water with ascorbic acid (1 g/l) was given in trials conducted by Balnave et al. (Reference BALNAVE, ZHANG and MORENG1991). The authors found that ascorbic acid prevented deleterious effect of saline water on eggshell quality. However ascorbic acid was not effective when administered after hens had been on saline water for several weeks.

Effect of saline water on broilers performance

Deyhim and Teeter (Reference DEYHIM and TEETER1995) found that drinking water supplemented with NaCl (0.067 mol/l) significantly increased weight gain and water consumption of broilers reared in thermoneutral and cycling heat stress environment, but had no effect on the plasma concentrations of Na⁺, K⁺, aldosterone or rectal temperatures. The results of this study indicated that broiler chickens kept in a heat stress environment are under osmotic stress and supplementing drinking water with 0.067 mol/l NaCl does not lessen this stress. Deyhim and Teeter (Reference DEYHIM and TEETER1991) mentioned that, at 35ºC, drinking water containing excess NaCl (0.39%) decreased venous PCO₂ and HCO₃^-, increased PO₂ but had no effect on venous pH and water consumption relative to heat–distressed control. NaCl failed to impact plasma corticosterone. The authors suggested that, to a lesser extent, NaCl reduces heat–distressed consequences by a mechanism as yet undefined.

Watkins et al. (Reference WATKINS, FRITTS, YAN, WILSON and WALDROUP2005) reported that elevated levels of Na and Cl either in the drinking water or in the diet produced significant effects on the performance of broilers. The significant interaction between dietary and water levels of these mineral on the broilers performance was also observed. The authors stated that Na and Cl in the drinking water should be considered when minerals requirements of broilers are being established, and must be adjusted accordingly.

Xiang et al. (Reference XIANG, SUN, ZHANG, LI, WANG and WANG2004) found that, drinking water containing 600 and 1200 mg/l Na from NaCl significantly increased the incidence of pulmonary hypertension syndrome and the right to total ventricle weight ratio (RV/TV). Shlosberg et al. (Reference SHLOSBERG, BELLAICHE, BERMAN, BEN DAVID and DEEB1998) reported that the addition of 1000 mg/l Na as NaCl to mains-derived town water significantly increased the incidence of mortality from ascites in cold–exposed broilers from days 28 to 47 of age.

Damron and Flunker (Reference DAMRON and FLUNKER1993) performed two broilers experiments, each lasting 21 days. A 5.25% sodium hypochlorite solution was used to provide chloride levels of 0, 10, 100, or 500 ppm in the first study, and 0, 150, 200, 250, 300, 350, 400, or 450 ppm in the second study. The authors found that water consumption was reduced in the 100 ppm chloride treatments, and body weight was impaired when receiving the 300 ppm Cl treatment.

Mushtag et al. (Reference MUSHTAG, SARWAR, NAWAZ, MIRZA and AHMAD2005) provided three levels of dietary sodium (0.20, 0.25 and 0.30%) and chloride (0.30, 0.40 and 0.50%) to broilers under subtropical summer conditions. Significantly dietary effect of Na⁺ x Cl ^– was noted for litter moisture and serum HCO₃^–. Birds fed diet containing 0.25% Na⁺ and 0.30% Cl ^– performed as well as those fed other diets when the cyclic temperature ranged from 32 to 39ºC.