Understanding the ideology of electrolyte balance

Electrolyte balance plays a vital role in acid-base balance and ultimately alters broiler performance. Metabolic and biochemical pathways cannot operate efficiently or maintain the physiological status of the bird without this correct balance. Supplementing Na and Cl along with K, in correct concentrations and balance, are essential for this hypothesis. Some basic equations (Melliere and Forbes, Reference MELLIERE and FORBES1966) have been developed to explain the relationship between cations and anions, as follows:

Relative level = mEq cation = Ca + Mg + Na + K

mEq anion = PO₄ + Cl + SO₄

In the above equation, only Na, K and Cl ions were considered to be crucial to maintain growth performance of broilers. Many reasons were provided to include these ions in the equation in which acid-base balance and bioavailability were key factors to be considered. It is imperative for broilers to regulate the intake and loss of these cations and anions from the diet (Mongin, Reference MONGIN1981). Furthermore, the electrolyte equilibrium can be described by a formula i.e. DEB including three main identified electrolytes. DEB is described as the percentage of different electrolytes converted into the standard units (i.e. mEq/kg) by multiplication using different factors that are derived from the elemental weight of the respective electrolyte, as follows:

DEB (mEq/kg) =% Na × 435 +% K × 256 –% Cl × 282

Initially, the state of acid base equilibrium was best given by the following equation that describes the health status of the birds:

(Anions – Cations) _Ingested + H⁺_endogenous= (Anions – Cations) _excreted

The production of endogenous acid (_endogenous H⁺) and excess bases (BEecf) are additional factors that were added by Mongin (Reference MONGIN1981) along with electrolytic (Na + K – Cl) intake and excretion:

(Na + K – Cl) _Ingested = (Anions – Cations) _excreted + H⁺ + BEecf _endogenous

Whenever diets are formulated with the concept of electrolyte balance, the varying levels of each electrolyte (Na, K and Cl) affect the DEB value in a different way. The DEB result (mEq/kg) can be altered by simply changing one, two or three electrolytes with varying growth responses in broilers, for example:

Na 0.25% + K 0.80% – Cl 0.22% = 252 mEq/kg DEB

Na 0.25% + K 0.72% – Cl 0.15% = 251 mEq/kg DEB

Na 0.20% + K 0.85% – Cl 0.20% = 249 mEq/kg DEB

Na 0.25% + K 0.85% – Cl 0.25% = 256 mEq/kg DEB

Na 0.40% + K 0.50% – Cl 0.20% = 250 mEq/kg DEB

It can be incurred from these equations that the DEB value of 250 mEq can be attained by varying the one or other values of each electrolyte. However, the level of each electrolyte is as important as that of DEB, according to the age of the bird. In practical diet formulations, ingredient composition can alter electrolytes and DEB e.g. increasing the level of soybean and fish meals results in higher K and Cl, respectively.

Dietary electrolytes and growth performance

An improvement in growth performance in broiler chickens was observed by varying the levels of Na, Cl and K, whilst changing DEB. It has been demonstrated that Na has an important role in feed intake (FI) just after hatching for stimulating the secretion and activity of certain digestive enzymes. Maiorka et al. (Reference MAIORKA, MAGRO, BARTELS, KESSLER and PENZ2004) observed a quadratic response for increasing Na levels (from 0.10 to 0.46%) in pre-starter diets on body weight gain (BWG), feed conversion ratio (FCR), FI and water consumption. Further, it has been suggested that optimal Na level is 0.45% for water consumption, 0.40% for FI and BWG, and 0.38% for FCR. These results were similar to the earlier findings of Vieira et al. (Reference VIEIRA, PENZ, POPHAL and GODOY DE ALMEIDA2003) who reported 0.38% and 0.40% Na for BWG and FCR respectively, for the first seven days of age. The level of dietary Na needed to optimise FCR was considered to be lower than needed to maximise BW and water intake (Watkin et al., Reference WATKINS, FRITTS, YAN, WILSON and WALDROUP2005). Ribeiro et al. (Reference RIBEIRO, KRABBE, PENZ, RENZ and GOMES2004) suggested a wide range of Na levels, from 0.31 to 0.48%, in pre-starter diets for optimum performance. Murakami et al. (Reference MURAKAMI, WATKINS, SALEH, ENGLAND and WALDROUP1997) observed that 0.20 to 0.25% Na was needed for maximum performance during first 21 days of growth. Later work suggested that requirements of Na in corn-soy diets were 0.28 and 0.25% (1-21 d) and 0.15% (21-42 d) for maximum performance in broilers (Murakami et al., Reference MURAKAMI, OVIEDO-RONDON, MARTINS, PEREIRA and SCAPINELLO2001; Rondon et al., Reference RONDON, MURAKAMI, FURLAN, MOREIRA and MACARI2001). Mushtaq (Reference MUSHTAQ2010) did not find consistent results across a phase-feeding system, and proposed 0.26% Na for starter diets. Recently, lower Na requirements have been advised for starter (d 1-14; 0.15%) and finisher (d 15-35; 0.11%) broiler diets (Jankowski et al., Reference JANKOWSKI, ZDUŃCZYK, JUŚKIEWICZ and KWIECIŃSKI2011a). Similarly, Koreleski et al. (Reference KORELESKI, SWIATKIEWICZ and AREZEWSKA2010) described better growth responses in diets containing up to 0.12% Na.

The K requirements in different growth phases and productive parameters in broilers have been evaluated. Oliveira et al. (Reference OLIVEIRA, ALBINO, ROSTAGNO, PÁEZ and CARVALHO2005) conducted an experiment in three phases viz. 8-21, 22-42 and 43-53 d, and recommended K requirements of 0.63, 0.71 and 0.80% respectively for optimised BWG. Previously, lower levels, viz. 0.50, 0.47 and 0.45% K were suggested by Rostagno et al. (Reference ROSTAGNO, ALBINO, DOZELE, GOMES, FERREIRA, OLIVEIRA and LOPES2000) for 1-21, 22-42 and 43-49 d, respectively. More recent work reported negative effects when increasing K (0.78-1.19%) on BWG and FCR during 1-35 d (Koreleski et al., Reference KORELESKI, SWIATKIEWICZ and AREZEWSKA2010). The deleterious effects of high level of cations might be associated, in part, with disturbed ABB per se.

When higher levels of Cl (0.21-0.31%) were supplemented in broiler feed, improved BWG and FCR were noticed in the starter phase (1-15 d) without affecting the rest of the period (16-42d; Koreleski et al., Reference KORELESKI, SWIATKIEWICZ and AREZEWSKA2011). Previously, the supplementation of 0.25% Cl has been recommended for the starter and finisher periods (Murakami et al., Reference MURAKAMI, OVIEDO-RONDON, MARTINS, PEREIRA and SCAPINELLO2001; Rondon et al., Reference RONDON, MURAKAMI, FURLAN, MOREIRA and MACARI2001). Zisman (Reference ZISMAN1986) observed higher BWG (from 735 to 741 g) when Cl was supplemented at higher levels, i.e. increased from 0.15 to 0.35%.

Leeson and Summers (Reference LEESON and SUMMERS2001) considered 250 mEq/kg DEB an appropriate level for adequate broiler growth, as inspired by the work of Mongin (Reference MONGIN1981). According to Murakami et al. (Reference MURAKAMI, SALEH, WATKINS and WALDROUP2000), a vast range of DEB (150 and 350 mEq/kg) may be suitable in commercial diets for maximum bird performance. Johnson and Karunajeewa (Reference JOHNSON and KARUNAJEEWA1985) found that DEB lower than 180 mEq/kg and higher than 300 mEq/kg affected the weight of the chickens at 42 d of age. The best DEB for maximum growth performance was determined to be between 245 and 315 mEq/kg for 1-21 d and between 249 and 261 mEq/kg from d 21 to 42 (Murakami et al., Reference MURAKAMI, OVIEDO-RONDON, MARTINS, PEREIRA and SCAPINELLO2001; Rondon et al., Reference RONDON, MURAKAMI, FURLAN, MOREIRA and MACARI2001). Likewise, Koreleski et al. (Reference KORELESKI, SWIATKIEWICZ and AREZEWSKA2011) recently observed similar responses of improved growth when DEB was dropped from 298 to 274 mEq/kg in the starter phase (1-15 d). During the finisher phase, 250 mEq/kg DEB gave the best results (Szabó et al., Reference SZABÓ, VUCSKITS, ANDRÁSOFSZKY, BERTA, BERSÉNYI, BÖRZSÖNYI, PÁLFI and HULLÁR2011). Similar results were noticed at 260 mEq/kg DEB when all growth parameters responded positively (Shahbaz et al., Reference SHAHBAZ, ALAM, NADEEM and ASHFAQ2004). Hulan et al. (Reference HULAN, DEGROOTE, FONTAINE, DEMUNTER, MCRAE and PROUDFOOT1985) determined the effect of DEB and varying levels of calcium, and found that the worst and best BWG were achieved when the DEB was 174 and 215 mEq/kg with 1.38 and 0.95% calcium, respectively. The FI was maximised when a DEB of 264 mEq/kg was attained by using Na, whereas DEB was altered (213 mEq/kg) when Na + K was used. However, a range of DEB (202-235 mEq/kg) was recommended for optimising FI from trial data where Na and Cl were used to alter DEB (Borges et al., Reference BORGES, FISCHER DA SILVA, MEIRA, MOURA, MAIORKA and OSTRENSKY2004b). Keeping in view such a complex situation, it can be proposed that not only DEB, but other contributing ions could change the effects of DEB. Moreover, not all the issues created by each ion and DEB can be fully resolved in broiler diets.

Dietary electrolytes, heat stress and growth performance

In more recent trials, varying electrolyte levels and DEB were used to evaluate broiler production performance with respect to the environment. Ambient temperature is considered as an important reason for altering the level of electrolytes or DEB, alongside considering ABB and internal homeostasis. Most of the electrolytes have been considered to be more potent when applied via water rather than an equivalent intake through feed (Dai et al., Reference DAI, BESSEI and QUANG2009), however nutritionists typically prefer the certainty of electrolyte inclusion in feed rather than water. This is due to the lower solubility of some electrolytes in water (e.g.) NaHCO₃ has a solubility of only 11% in water at 37.8°C.

Yalcin et al. (Reference YALCIN, SETTAR, OZKAN and CAHANER1997) reported a reduction in BW (23%) and FI (15%) for broilers reared under high temperatures (min. 27°C and max. 38°C) when compared with counterparts reared under temperate conditions. The FI decreased by between 7 and 14% in birds reared at 27°C compared with those kept at 21°C during the finisher phase (4-6 weeks of age; Suk and Washburn, Reference SUK and WASHBURN1995). It has been proposed by Zuprizal et al. (Reference ZUPRIZAL, CHAGNEAU and GERAERT1993) that this reduction equated to 3.6% lower FI per degree increase in temperature (between 22 and 32°C), which may also be related to the age and genotype of the birds. Therefore, extra supplementation of electrolytes can be favourable for birds under heat stress condition. From 1-28 d, higher BWG was observed in birds fed 0.25% compared to 0.20 or 0.30% Na (Mushtaq et al., Reference MUSHTAQ, SARWAR, NAWAZ, MIRZA and AHMAD2005). In addition, a combination of 0.25% Na and 0.30% Cl (250 mEq/kg DEB) was recommended for better performance. Interestingly, supplementation with Na, Cl or Na × Cl in combination did not affect growth performance for 28-42 d broilers raised in sub-tropical summer conditions (Mushtaq et al., Reference MUSHTAQ, MIRZA, ATHAR, HOOGE, AHMAD, AHMAD, MUSHTAQ and NOREEN2007).

The addition of K in drinking water ameliorated problems with BW in broilers kept under hot summer conditions (Smith and Teeter, Reference SMITH and TEETER1987). Rao et al. (Reference RAO, NAGALAKSHMI and REDDY2002) suggested that, for maximum BWG in broilers, a daily K intake of 0.12-0.23% was needed. Similar improvements in BWG were observed in birds with heat stress when graded levels of K (from 0.05 to 0.15%) were supplemented (Teeter and Smith, Reference TEETER and SMITH1986). In the recent past, relatively high K (0.9-1.0%) resulted in better feed-efficacy (FCR), those levels being higher than recommended by NRC for birds kept in the condition of heat stress (Ribeiro et al., Reference RIBEIRO, KESSLER, VIOLA, SILVA, RUBIN, RABER, PINHEIRO and LECZNIESKI2008). Heat stress is considered responsible for loss of plasma K, however, supplementing extra K in the diets does not exacerbate it further.

Borges et al. (Reference BORGES, FISCHER DA SILVA, ARIKI, HOOGE and CUMMINGS2003) demonstrated that 240 mEq/kg DEB optimised BWG and FCR in hot summer conditions. In subsequent work, Borges et al. (Reference BORGES, FISCHER DA SILVA, MEIRA, MOURA, MAIORKA and OSTRENSKY2004b) recommended 202-235 mEq/kg under normal ambient temperature, showing that higher DEB requirements exist for heat stress compared to normal ambient conditions. Maximum BWG and FI were predicted at 200-220 mEq/kg DEB in male broilers at 42 d of age kept under conditions less than 35°C in temperature (Borges et al., Reference BORGES, FISCHER DA SILVA, ARIKI, HOOGE and CUMMINGS2003). Borgatti et al. (Reference BORGATTI, ALBUQUERQUE, MEISTER, SOUZA, LIMA and TRINDADE NETO2004) proposed a DEB between 290 to 330 mEq/kg for 1 to 21 d birds, while Ahmad et al. (Reference AHMAD, MUSHTAQ, KHAN, BABAR, YOUSAF, HASAN and KAMRAN2009) suggested 150-250 mEq/kg DEB for the well-being of heat-distressed broilers aged 1 to 42 d. From such published data it can be seen that relatively high levels of electrolytes, particularly cations are recommended for heat stress conditions. However, a high range of DEB (i.e. 200-300 mEq/kg) has been suggested to be sufficient under various situations of high temperature.

Dietary electrolytes, salts and growth performance

The addition of various salts to the feed or water can alter physiological response and ABB in broilers. The requirement for dietary electrolytes (Na, K and Cl) decreases with increasing age (NRC, 1994), however, requirements for electrolytes and their respective salts tend to be varied for different growth and physiological parameters under varying conditions of ambient temperature and relative humidity. Additionally, the form and purity of the salts are important in determining the efficacy of a particular electrolyte. Among the supplemental salts, potassium chloride (KCl), hydrochloric acid (HCl), ammonium chloride (NH₄Cl), calcium chloride (CaCl₂), sodium hydroxide (NaOH) and sodium chloride (NaCl) are considered as strong electrolytes while sodium bicarbonate (NaHCO₃) and acetic acid (CH₃COOH) are classed as weak electrolytes (Mongin, Reference MONGIN1981; Hooge, Reference HOOGE2003).

Nutritionists can manage hot summer conditions using different salts via feed or water, so that the detrimental effects of heat stress can be minimised. Formulating feed to an optimum DEB using NaHCO₃ to avoid excessive mortality and stimulate growth of broilers could be a possible preventive measure during heat-stress conditions. Various researchers (Mongin, Reference MONGIN1981; Hooge, Reference HOOGE2003; Ahmad et al., Reference AHMAD, SARWAR and MAHR–UN–NISA2005) have recommended NaHCO₃ as a salt of choice during heat-stress because of the presence of Na and HCO₃. Gorman and Balnave (Reference GORMAN and BALNAVE1994) suggested that heat stress might induce a requirement for HCO₃^– due to the development of metabolic acidosis. Under such conditions, the responses of birds was better in diets supplemented with NaHCO₃ (a CO₂ generating buffer) compared to Na₂CO₃ for the same dietary Na and DEB levels. Owen et al. (Reference OWEN, WIDEMAN, LEACH, COWEN, DUNN and FORD1994) reported beneficial effects of dietary NaHCO₃ when it was incorporated at a dietary level of 1%, whereby it caused a reduction in ascites, ascribed to the alkaline nature of the salt and the possible induction of alkalosis. Dietary NaHCO₃ added at 3.2 g/l had no effect on blood pH, whereas a short-term infusion of 2.0 g/l into the crop did induce alkalosis (Bottje and Harrison, Reference BOTTJE and HARRISON1985). The supplementation of Na as NaHCO₃ at 1.4 g/l was deemed harmful, as it reduced BW and increased mortality from ascites (Julian et al., Reference JULIAN, FRIARS, FRENCH and QUINTON1986), whereas a very high level of 7.5 g/l was found to be toxic after 14 d of age (Mirsalimi et al., Reference MIRSALIMI, JULIAN and SQUIRES1993). Under heat stress conditions, Balnave and Gorman (Reference BALNAVE and GORMAN1993) suggested that the supplementation of NaHCO₃ at a level of 5.6 g/l in the water did not reduce BW. This might might be due to the diets fortified with NaHCO₃ that improved FI at high temperatures (Balnave and Gorman, Reference BALNAVE and GORMAN1993). It was observed that about a quarter of broiler companies in America use either NaHCO₃ or NaHCO₃•Na₂CO₃•2H₂O (sodium sesquicarbonate) in the summer months to combat heat stress (Donohue, Reference DONOHUE2001). Benton et al. (Reference BENTON, BALNAVE and BRAKE1998) stated that NaHCO₃ can be incorporated into broiler diets up to 0.5% and is recognised by saving two days of growth to market weight during summer in Australia. Further, it was suggested that heat-stressed broilers efficiently responded to supplemental NaHCO₃ as compared to those fed KHCO₃, Na₂CO₃ or K₂CO₃. Ahmad et al. (Reference AHMAD, MUSHTAQ, SARWAR, HOOGE and MIRZA2006) stated that the sodium non-chloride salts (NaHCO₃, Na₂CO₃ and Na₂SO₄) resulted in better performance and reduced mortality as compared to sodium chloride salts in heat-stressed broilers.

Supplementing diets with NaHCO₃ or NaCl (to provide Na 0.2%, 0.3% or 0.45%) improved growth performance in broiler chicks (Arbor Acres) reared under high temperatures i.e. 32.5°C (Nagwa and Maghraby, Reference NAGWA and MAGHRABY1995). Moreover, diets supplemented with higher levels of NaCl improved FI compared to lower doses. However, the supplementation of NaHCO₃ in drinking water did not affect FI in 42-56 day-old broilers exposed to severe heat (Branton et al., Reference BRANTON, REECE and DEATON1986). Bláha et al. (Reference BLÁHA, DRASLAROVÁ and KROESNA2000) reported that broiler diets (Hybrid Cobb) containing 0.5% NaCl and 35 mg vitamin C showed better FCR than those fed unsupplemented diets. Dai et al. (Reference DAI, BESSEI and QUANG2009) noted the same effect in trials where 0.4% NaCl showed better growth characteristics. Conversely, using non-conventional Na salt sources such as Na-fluoride and Na-silicate did not influence growth rates, FCR and mortality; however, bone characteristics were improved by Na-fluoride, and, to some extent with Na-silicate (Merkley and Miller, Reference MERKLEY and MILLER1983).

When salts of Na were compared to the salts of K, it was noted that dietary NaHCO₃ significantly ameliorated FCR compared to supplements of KHCO₃ on equimolar bicarbonate concentration at 31°C (Hayat et al., Reference HAYAT, BALNAVE and BRAKE1999). Previously, KHCO₃ supplements have been shown to reduce FCR in chronic heat stress conditions (Teeter and Smith, Reference TEETER and SMITH1986). Smith and Teeter (Reference SMITH and TEETER1987) studied dietary levels of 1.5-2.0% K from KCl and reported improved FCR during chronic heat stress. The supplementation of KCl in cold water (10-27°C) augmented FI and BWG whereas its supplementation in warm (44°C) drinking water had no beneficial effect on FI or BWG of heat-stressed broilers (Beker and Teeter, Reference BEKER and TEETER1994). When K salts were supplemented in feed as a sole source of K, better health status was observed in broilers (Ahmad et al., Reference AHMAD, SARWAR and MAHR–UN–NISA2005). Deyhim and Teeter (Reference DEYHIM and TEETER1995) reported no effects of isomolar KCl or NaCl (0.067 mol/l) supplementation in drinking water on birds kept under thermo-neutral or cyclic heat stress. Teeter and Smith (Reference TEETER and SMITH1986) reported maximum BWG in broilers at 35°C with 2 g/kg NH₄Cl added in drinking water. The supplementation of dietary NH₄Cl up to 3 g/kg did not affect performance and improved the growth rate of heat stressed broilers. However, higher levels of NH₄Cl, e.g. >1%, caused a numerical increase in ascites. This was presumed to be due to the acidifying nature NH₄Cl that lead to the possible induction of acidosis (Owen et al., Reference OWEN, WIDEMAN, LEACH, COWEN, DUNN and FORD1994). Likewise, the dietary NH₄Cl at a concentration of 6.3 g/l in the drinking water caused a marked rise in blood acidity in 42-52 day old broilers (Branton et al., Reference BRANTON, REECE and DEATON1986). Bottje and Harrison (Reference BOTTJE and HARRISON1985) suggested that treating heat stressed broilers with NH₄Cl could potentially be deleterious to the bicarbonate buffer system, as any metabolic acidosis associated with NH₄Cl catabolism might accentuate HCO₃⁻ loss due to higher respiratory rate. However, the bicarbonate buffering system needs special care in broilers due to typically lower disease resistance than layers.

The above discussion suggests that the supplementation of NaHCO₃ and KCl under heat stress could be a useful tool to maintain ABB and to attain improved performance in broilers, especially under heat stress condition. Moreover, NaCl and NH₄Cl should be used carefully to maintain a proper level of electrolytes and their balance i.e. DEB. The supplementation of such salts should be used carefully to compensate for excretory losses of electrolytes.

Dietary electrolytes, water consumption and litter quality

Water consumption increases linearly with increasing electrolytes in the diet (Mongin, Reference MONGIN1980; Borges et al., Reference BORGES, ARIKI, SANTIN, FISCHER DA SILVA and MAIORKA2002). Higher levels of electrolytes cause osmotic changes in the intestinal lumen of the birds and can enhance water retention in the digesta (Murakami et al., Reference MURAKAMI, SALEH, WATKINS and WALDROUP2000). Mongin (Reference MONGIN1980) suggested a vital relationship between excessive Na intake and litter moisture. Likewise, the supplementation of K can be considered in this regard, while the role of Cl is considered inconsequential (Murakami et al., Reference MURAKAMI, OVIEDO-RONDON, MARTINS, PEREIRA and SCAPINELLO2001; Rondon et al., Reference RONDON, MURAKAMI, FURLAN, MOREIRA and MACARI2001). Borges et al. (Reference BORGES, ARIKI, SANTIN, FISCHER DA SILVA and MAIORKA2002) suggested that diets with high levels of Cl and/or K did not stimulate water intake during the first seven days of age.

It has been noticed that litter moisture and crustiness are the most prevalent causes of foot-pad dermatitis, a form known as ‘contact dermatitis’ (Greene et al., Reference GREENE, MCCRACKEN and EVANS1985) in chickens that is caused by irritants present in the litter. This type of foot-pad dermatitis seems to be related mainly to litter moisture and excreta sticking to the skin. Diets based on different ingredients show variations in water intake that in turn could alter excreta and litter moisture characteristics. Eichner et al. (Reference EICHNER, VIEIRA, TORRES, CONEGLIAN, FREITAS and OYARZABAL2007) attributed the relationship of litter moisture and the incidence and severity of foot-pad dermatitis to dietary ingredients. Such diets are mainly based on vegetable sources, e.g. soybean meal, as compared to animal protein sources. This problem in high soybean diets can be linked with high K content and excretion rates. Further, litter moisture and the severity of foot-pad dermatitis is aggravated as broilers get older, e.g. approaching 40 d. At this age, water consumption, FI and excreta production per square foot increases rapidly.

Diets formulated with higher Na and K increased water intake and litter moisture, whereas an increase in Cl does not appear to have such effects (Murakami et al., Reference MURAKAMI, SALEH, WATKINS and WALDROUP2000; Reference MURAKAMI, OVIEDO-RONDON, MARTINS, PEREIRA and SCAPINELLO2001; Rondon et al., Reference RONDON, MURAKAMI, FURLAN, MOREIRA and MACARI2001). Mushtaq et al. (Reference MUSHTAQ, PASHA, AKRAM, MUSHTAQ, PARVIN, CHOI, HWANGBO and KIM2013b) recorded a similar observation when increasing Cl did not show any effect on water consumption. Borges et al. (Reference BORGES, ARIKI, SANTIN, FISCHER DA SILVA and MAIORKA2002) showed that diets containing 0.30 and 0.45% Na caused higher litter moisture. Mushtaq et al. (Reference MUSHTAQ, PASHA, AKRAM, MUSHTAQ, PARVIN, FAROOQ, MEHMOOD, IQBAL and HWANGBO2013a) observed similar results for water intake by increasing Na (0.17-0.44%), whilst a lower increase in Na levels (0.08-0.17%) did not affect litter moisture (Jankowski et al., Reference JANKOWSKI, JUŚKIEWICZ, ZDUŃCZYK, SMIECINSKA and KWIECIŃSKI2011b). It has been stated that faecal moisture has a positive association with total dietary Na and Na:Cl ratio. Increasing levels of Na (0.17-0.26%) along with Cl (0.34-0.48%) elevated excreta moisture (Jankowski et al., Reference JANKOWSKI, ZDUŃCZYK, JUŚKIEWICZ and KWIECIŃSKI2011a). A strong negative correlation was found between water consumption and mortality by Branton et al. (Reference BRANTON, REECE and DEATON1986), but did not show any correlation with litter moisture. Increasing the level of K (0.78-1.19%) did not show any effect on water intake (Koreleski et al., Reference KORELESKI, SWIATKIEWICZ and AREZEWSKA2011).

The consequence of higher water intake promoted by diets with high DEB leads to higher litter moisture and leg health issues. Supplementation of varying DEB levels in drinking water did not affect litter moisture contents across several studies (Karunajeewa et al., Reference KARUNAJEEWA, BARR and FOX1986; Salvador et al., Reference SALVADOR, ARIKI, BORGES, PEDROSO and MORAES1999) while other researchers (Balnave and Gorman, Reference BALNAVE and GORMAN1993; Nagwa and Maghraby, Reference NAGWA and MAGHRABY1995; Borges et al., Reference BORGES, ARIKI, SANTIN, FISCHER DA SILVA and MAIORKA2002) reported that this is directly related to DEB. High DEB diets can increase blood osmolarity, especially in the presence of Na. However, Maiorka et al. (Reference MAIORKA, MAGRO, BARTELS, KESSLER and PENZ2004) did not find any effect of DEB (from 100 to 300 mEq) on excreta moisture up to seven days of age when DEB was changed using dietary Na. Borges et al. (Reference BORGES, ARIKI, SANTIN, FISCHER DA SILVA and MAIORKA2002) confirmed that there was no effect of DEB (246-277 mEq/kg) on the litter moisture. Castelló and Pontes (Reference CASTELLÓ and PONTES1992) reported lower water intake and higher litter moisture contents with low DEB diets i.e. 170-174 mEq/kg, compared with 336-340 mEq/kg. Likewise, Karunajeewa and Barr (Reference KARUNAJEEWA and BARR1988) observed higher litter moisture in diets with a DEB of 200 versus 100 mEq/kg. It was speculated that the increased water consumption is not the result of higher DEB, but is because of increased supplementation of cations (Na or K), which elevates DEB. When DEB value was reduced with increasing dietary Cl contents, water consumption and excreta moisture were not affected (Koreleski et al., Reference KORELESKI, SWIATKIEWICZ and AREZEWSKA2011). The bird is not able to retain extra water in the body, which is then reflected in increased faecal moisture or litter wetness. It can be deduced from the above discussion that increasing DEB with Na and Cl can influence water intake and litter moisture while the role of increasing supplementation of Cl in this regard is not decisive.

Dietary electrolytes, heat stress, water consumption and litter quality

A strong relationship between dietary electrolytes and water consumption, especially in hot climatic conditions, is not denied. This is a likely response to cations (Na and K) and appears to be mediated by cells of the hypothalamus involved in osmoregulation. This physiological response has been used as a tool to alleviate increased internal body temperature especially under heat stress conditions. It has been established that increasing dietary Na has a parallel response in terms of water consumption in heat-distressed broilers (Mushtaq et al., Reference MUSHTAQ, SARWAR, NAWAZ, MIRZA and AHMAD2005). However, these reported results were specific to younger birds. Moreover, birds with high initial weights excreted less moisture through droppings. This demonstrated the ability of the heavier birds to retain more water in the body, leading to improved litter condition (Mushtaq et al., Reference MUSHTAQ, MIRZA, ATHAR, HOOGE, AHMAD, AHMAD, MUSHTAQ and NOREEN2007).

It has been stated that litter moisture is associated with the concentration of Na and Cl in the diet, which are the regulatory factors of body fluids. Mushtaq et al. (Reference MUSHTAQ, SARWAR, NAWAZ, MIRZA and AHMAD2005; Reference MUSHTAQ, MIRZA, ATHAR, HOOGE, AHMAD, AHMAD, MUSHTAQ and NOREEN2007) established a relationship between Na and Cl in heat-distressed broilers. Increased water intake and litter moisture were observed for higher dietary levels of Na (0.30%) and Cl (0.50%), respectively, during 1-28 d of age in broilers. From 28-42 d of age, water consumption was greater at 0.20% Na as compared to higher levels of Na (0.25 or 0.30%), without any effect of dietary Cl. It is clear that birds were sensitive to the levels of electrolytes initially, but become resistant to Cl changes during the finisher phase (Mushtaq et al., Reference MUSHTAQ, SARWAR, NAWAZ, MIRZA and AHMAD2005; Reference MUSHTAQ, MIRZA, ATHAR, HOOGE, AHMAD, AHMAD, MUSHTAQ and NOREEN2007).

There is a direct relationship between DEB of the diet and water consumption in birds. Lower water consumption was seen at lowest DEB i.e. 0 mEq/kg, and highest at elevated DEB i.e. 350 mEq/kg in hot summer conditions (Ahmad et al., Reference AHMAD, MUSHTAQ, KHAN, BABAR, YOUSAF, HASAN and KAMRAN2009). This problem is more pronounced in part of the broilers’ later life. Borges et al. (Reference BORGES, FISCHER DA SILVA, MEIRA, MOURA, MAIORKA and OSTRENSKY2004b) observed higher water intake at a high level of DEB (240 mEq/kg) when compared with 0 mEq/kg. As DEB increases (from 50 to 340 mEq/kg) this amplifies litter moisture and bacterial contamination accordingly; and reduces the quality of litter in moderate (Borges et al., Reference BORGES, FISCHER DA SILVA, MEIRA, MOURA, MAIORKA and OSTRENSKY2004b) and high (Ahmad et al., Reference AHMAD, MUSHTAQ, KHAN, BABAR, YOUSAF, HASAN and KAMRAN2009) ambient temperatures. Moisture contents of litter may be altered by excreta composition, which can affect water retention and limit evaporative water losses (Francesch and Brufau, Reference FRANCESCH and BRUFAU2004). Borges et al. (Reference BORGES, FISCHER DA SILVA, ARIKI, HOOGE and CUMMINGS2003) reported high litter moisture (i.e. 21%) with 360 mEq/kg DEB during the first week of age and went up to 55% litter moisture at six weeks of age. Borges et al. (Reference BORGES, FISCHER DA SILVA, MEIRA, MOURA, MAIORKA and OSTRENSKY2004b) reconfirmed similar findings of high litter moisture in older birds fed a diet containing 340 mEq/kg DEB. Water intake and litter quality parameters were affected by increased K levels in the diet (Pesti et al., Reference PESTI, CERVANTES, BAKALLI, BAFUNDO and GARCIA1999). Smith and Teeter (Reference SMITH and TEETER1987) stated that heat stress increased K excretion through urine, resulting in a decrease in plasma K (Smith and Teeter, Reference SMITH and TEETER1987). Ahmad et al. (Reference AHMAD, SARWAR and MAHR–UN–NISA2005) suggested increased levels of Cl in drinking water could cause water:feed ratio and excreta moisture to increase.

This information, taken as a whole, suggests that increasing cations (Na and K) is not the only solution for heat stress conditions, but it may be important to manage DEB more critically by keeping the level of cations at a higher level and anions on lower level.

Dietary electrolytes, salts, water consumption and litter quality

The significance of electrolytes and their respective salts becomes more vital when environmental norms, temperature and relative humidity, are considered for water consumption and dampness of litter material. Moreover, various other attributes are responsible for litter quality, such as housing and management (type of litter, ventilation, density, heating system, drinking system) and disease factors (coccidiosis, E-Coli, Campylobacter; Francesch and Brufau, Reference FRANCESCH and BRUFAU2004). It is considered that using different salts in the feed/ water determines the amount of water intake in broilers (Mongin, Reference MONGIN1980) and, in parallel, assists the birds in coping with heat stress.

The addition of various salts to the diet and/or drinking water alters the bird's osmotic balance, increases water consumption and excretion to maintain fluid balance in the body (Borges et al., Reference BORGES, FISCHER DA SILVA, MEIRA, MOURA, MAIORKA and OSTRENSKY2004b). However, NaHCO₃ is considered a good source of Na and HCO₃^– ions in heat stress conditions (Hooge, Reference HOOGE2003). Diets containing NaHCO₃ resulted in higher water intake, water:feed ratio and litter moisture than diets containing Na₂CO₃ and Na₂SO₄ (Ahmad et al., Reference AHMAD, MUSHTAQ, SARWAR, HOOGE and MIRZA2006). It might also indicate changes in plasma osmolarity, which further influences the thirst centre in the brain (Borges et al., Reference BORGES, FISCHER DA SILVA, MAJORKA, HOOGE and CUMMINGS2004a; Ahmad et al., Reference AHMAD, SARWAR and MAHR–UN–NISA2005). Likewise, the supplementation of KHCO₃ has been shown to induce more pronounced changes in water consumption and excreta moisture than Na₂CO₃ and Na₂SO₄. Branton et al. (Reference BRANTON, REECE and DEATON1986) reported no difference in water intake with NH₄Cl (0.63%) and NaHCO₃ (0.32%) through drinking water supplementation during periods of heat stress. In contrast, the water intake was increased by about 20% in birds given water supplemented with NaHCO₃ (0.63%) and was severely limited by the supplementation of NH₄Cl (0.31%). It is still unclear that the beneficial effects of the salt are either because of maintaining electrolyte balance and blood pH or by increasing water intake (Leeson and Summers, Reference LEESON and SUMMERS2001; Ahmad et al., Reference AHMAD, KHALID, MUSHTAQ, MIRZA, NADEEM, BABAR and AHMAD2008). Deyhim and Teeter (Reference DEYHIM and TEETER1995) reported that drinking water supplemented with either isomolar (0.067 mol/l) NaCl or KCl, substantiated the higher water consumption in heat-distressed broilers. Borges et al. (Reference BORGES, ARIKI, DA SILVA, MAIORKA and LAURENTIZ2000) reported an increased water intake in broilers supplemented with 1.0% KCl during the finisher phase. In other trials, Ahmad et al. (Reference AHMAD, KHALID, MUSHTAQ, MIRZA, NADEEM, BABAR and AHMAD2008) observed a similar response in broilers when the drinking water was supplemented with 0.6% KCl. Earlier work by Smith and Teeter (Reference SMITH and TEETER1992) gave clear evidence that KCl increased the water:feed ratio. However, when NH₄Cl was added in the diet, it increased water:feed ratio and litter moisture (Ahmad et al., Reference AHMAD, SARWAR and MAHR–UN–NISA2005).