Use of electrolyte and betaine water supplementation to support improved liveweight gain of commercial Pekin ducks exposed to adverse high temperature in the week prior to processing

Introduction

During periods of high temperature, commercial meat birds dissipate excess heat by panting and this results in excretion of CO₂ at a rate greater than cellular production. This can result in respiratory alkalosis as the HCO₃⁻ concentration in blood increases. Coupled with Na⁺ and K⁺ ions, the kidney excretes HCO₃⁻ in an effort to restore normal blood pH (Johnson 2008; Wasti et al. 2020). The loss of these ions can result in an acid–base imbalance (Borges et al. 2007; Popoola et al. 2020a), which is detrimental to bird performance (Ahmad et al. 2009; Mushtaq et al. 2013). The acid–base imbalance affects enzyme activities and can result in metabolic disorders (Mushtaq et al. 2013).

Supplying additional electrolytes in feed or water are strategies used to replace electrolyte losses and help meat birds cope with the electrolyte imbalance caused by heat stress (Lin et al. 2006; Mushtaq et al. 2013; Roushdy et al. 2018; Shao et al. 2019; Popoola et al. 2020b). The diet electrolyte balance (DEB) participates in acid–base regulation (Murakami et al. 2001; Sayed and Downing 2015; Popoola et al. 2020a; Araujo et al. 2022) and the concentrations of Na⁺, K⁺ and Cl⁻ are used to estimate DEB as milliequivalents per kilogram (mEq/kg; Mongin 1981).

Effects of DEB depend on the basal diet, genotype, temperature, and the electrolytes used and the relative concentrations of these (Borges et al. 2003; Ahmad et al. 2005; Ahmad and Sarwar 2006; Mushtaq et al. 2013; Popoola et al. 2020a; Yu et al. 2022). This means that identifying an optimal DEB would be difficult and could account for the variation in published results. Under thermoneutral conditions, a DEB ranging from 200 to 330 mEq/kg has been shown to support best performance in different studies (Johnson and Karunajeewa 1985; Borges et al. 2004; Szabó et al. 2011; Popoola et al. 2020b).

Under summer conditions, a DEB of 240 mEq/kg is optimal (Borges et al. 2003), whereas under tropical conditions (temperature range of 26.1–37.5°C) bird performance has been shown to be poorer when the DEB is 0 and 350 mEq/kg than when it is 50 or 250 mEq/kg (Ahmad et al. 2009). At high temperature, a range of 150–250 mEq/kg was found suitable by Ahmad et al. (2009). A DEB of 240 and 270 mEq/kg enhances protein efficiency, liveweight gain (LWG) and feed efficiency under high temperature (Popoola et al. 2020b). At 29–34°C, diets with a DEB of 120, 220 and 320 mEq/kg, when fed to finisher meat birds, have been shown to have no effect on performance (Saki et al. 2016).

Consequences of high ambient temperature causing heat stress (HS) in meat chickens are reduced LWG and feed intake (FI), with resultant poorer feed conversion efficiency (FCR) (Mushtaq et al. 2013; Zhong et al. 2018; Liu et al. 2019: Shin et al. 2019; Downing 2022). At high temperature (27–38°C), FI was 15% lower (Yalcin et al. 1997) and even at a moderately high temperature of 27°C FI was 7–14% lower than at 21°C (Suk and Washburn 1995). Supplying electrolytes in drinking water rather than in feed could compensate for their reduced uptake associated with the lower FI (Dai et al. 2009) during high temperature. Salts of sodium and potassium (NaCl, Na₂CO₃, KCl and K₂CO₃) are common water supplements used to support poultry during HS (Smith and Teeter 1993; Smith 1994; Mushtaq et al. 2013; Wasti et al. 2020). Under high ambient temperatures, providing NaHCO₃-supplemented drinking water has been reported to improve broiler performance and survivability (Ahmad et al. 2006). Using a combination of NaHCO₃, NaCl and KCl helps improve the performance of meat chickens exposed to high temperature (Downing et al. 2017; Elshafaei et al. 2020). The effect of electrolytes, at different inclusion rates, have proved beneficial under different, challenging high temperatures regimes.

The effects that DEB and water electrolyte supplementation have on Pekin duck performance have received limited investigation. Of the limited research, most has examined the effects of DEB on egg-laying duck strains (Wang et al. 2011; Nawab et al. 2018). So, under high temperature stress Pekin ducks can achieve greater electrolyte intake by increasing DEB or supplementing the water. However, it is often difficult to predict periods of adverse high temperature, so providing supplemented water provides management with the potential to supply extra electrolytes with limited warning of upcoming, challenging high-temperature conditions. In a previous publication, providing water supplemented with electrolytes and betaine improved LWG in Pekin ducks exposed to a high-temperature thermal challenge in the final week of the 6-week production cycle (Downing 2022).

Betaine is a trimethyl derivative of glycine and can function as a methyl-group donor, an organic osmolyte and antioxidant (reviewed by Saeed et al. 2019, Mishra et al. 2021 and Alagawany et al. 2022). As an osmolyte, betaine can help regulate osmotic pressure in cells and help limit dehydration during HS (Sayed and Downing 2015; Al-Abdullatif et al. 2021). When included as a feed additive, betaine can improve commercial chicken and duck performance and meat quality, especially when they are exposed to high-temperature HS (Liu et al. 2019; Park and Zammit 2019; Shin et al. 2019; Al-Garadi et al. 2023).

In earlier studies, Cherry Valley Pekin ducks were fed a basal diet, or the same diet supplemented with either 400, 800 or 1200 mg/L betaine in the drinking water and exposed to cyclic high temperature (33–43°C for 6 h daily 22°C) on Days 22–42 of age (Shin et al. 2019). The betaine supplemented from the lowest to highest rates supported higher LWG by 9.8%, 10.4% and 15.7% respectively. The improved growth was supported by increases of 9.2%, 7.6% and 10.1% in FI. The supplements also increased the plasma Na⁺, K⁺ and Cl⁻ electrolyte concentrations. Meat ducks during 22–42 days of age were exposed to thermo-neutral (TN) temperature of 24°C, high temperature (HT) of 34°C for 5 h/day, and feed withdrawal (5 h both morning and evening) and supplied with 800 g/kg betaine in the feed. The cyclic HT depressed LWG by 28.6%, while the betaine supplementation limited this to 10.1%. Interestingly, the researchers included a fourth treatment where betaine was included in the feed along with 300 mg/L of ascorbic acid in the drinking water, and this supported LWG equivalent to that of the TN control birds (Park and Zammit 2019).

The objective of the current experiment was to assess the effects that DEB and different concentrations of a previously used water electrolyte supplement had on the growth performance of Pekin ducks exposed to cyclic high ambient temperature during the last week of a 41-day production cycle. The working hypothesis was that increased electrolyte intake would benefit performance during the period of high temperature and that this could be met by increasing DEB or electrolyte supplementation of the water.

Materials and methods

All experimental protocols were approved by the University of Sydney Animal Care and Ethics Committee (Protocol: 2013/5903) and complied with the Australian Code of Practice for the use of Animals for Scientific Purposes National Health and Medical Research Council (2013).

Results

Temperature and humidity

The average daily temperature and humidity are shown in Fig. 1. The average daily temperature during the 9 h of high-temperature challenge was 28.8 ± 0.1°C (range 25.1–31.0°C) and humidity 81.7 ± 1.2%. For the remainder of the day, the temperature averaged 23.7 ± 0.1°C and humidity 87.7 ± 0.8%. On the basis of the average temperatures and RH, the average THI during the 9 h of the high-temperature period was 81.6% and during the remainder of the day it was 74.7%, but this included the transition period (from 17:30 hours to 19:30 hours) when the shed was returning to thermo-neutral conditions and the THI averaged 78.1%. During the high-temperature challenge, on the basis of the criteria of Moraes et al. (2008), birds would have experienced ‘severe discomfort’.

Fig. 1.

The average daily temperature and humidity over Days 36–41 of age when birds were exposed to high temperature for 9 h/day high.

Total electrolyte intake during the high temperature (D36–41)

The sodium, potassium, and chloride electrolyte intakes over D36–41 from the diet and supplements are given in Table 3. The supplement provided (P < 0.001) and diet DEB (P < 0.001) affected electrolyte intakes. The monovalent cation–anion difference (CAD) as milliequivalents (mEq) was calculated as follows (Moore et al. 2000):

CAD (mEq)=intake (Na++K+) mEq–intake (Cl−) mEq

The total electrolyte intake for birds on the L-DEB and H-DEB diets are given in Table 4. The birds on the L-DEB diet had a CAD of 38.3 ± 0.6 mEq/day and those on the H-DEB diet a CAD of 47.8 ± 0.6 mEq/day. Birds on the E150 supplement (58.8 ± 0.8 mEq/day) had the highest CAD, followed in order by E100 (48.7 ± 0.8 mEq/day), E100 + 36 h (48.7 ± 0.8 mEq/day) and E50 (39.7 ± 0.8 mEq/day), all being different from CAD of birds on BF (32.3 ± 0.8 mEq/day) and water alone (31.7 ± 0.8 mEq/day), which had equivalent values of CAD (all, P < 0.05).

Table 4.The sodium, potassium and chloride consumed from the diet and water supplements during the high-temperature period.

Treatment	Monovalent ion										CAD
	Diet	Na+	K+	Cl−	Na+	K+	Cl−	Na+	K+	Cl−
		mEq
		Diet contribution			Water contribution			Sum (diet + water)
Control	L-DEB	10.2	24.7	8.0	0	0	0	10.2	24.7	8.0	27.0
BF	L-DEB	10.5	25.3	8.2	0	0	0	10.5	25.3	8.2	27.6
E50	L-DEB	10.4	25.1	8.1	20.6	5.2	18.0	31.0	30.3	26.1	35.1
E100	L-DEB	10.5	25.5	8.2	43.2	10.9	37.8	53.8	36.3	46.1	44.1
E150	L-DEB	10.7	25.8	8.3	70.1	17.6	61.3	80.7	43.4	69.6	54.5
E100 + 36 h (HT)	L-DEB	10.2	24.6	7.9	39.1	9.8	34.2	49.2	34.4	42.1	41.5
Control	H-DEB	25.3	26.5	15.5	0	0	0	10.2	24.7	8.0	36.3
BF	H-DEB	25.8	27.0	15.8	0	0	0	10.5	25.3	8.2	37.0
E50	H-DEB	25.3	26.4	15.5	21.5	5.2	18.0	31.0	30.3	26.1	44.3
E100	H-DEB	25.4	26.6	15.6	46.0	10.9	37.8	53.8	36.3	46.1	53.8
E150	H-DEB	24.8	26.0	15.2	73.1	17.6	61.3	80.7	43.4	69.6	63.1
E100 + 36 h (HT)	H-DEB	25.9	27.1	15.9	39.6	9.8	34.2	49.2	34.4	42.1	52.1

Pekin ducks were fed a grower diet with a low DEB or with a high DEB (Days 15–35) and the same diets (Days 36–41) and exposed to high ambient temperature for 9 h/day and provided with water alone (water), betaine in the feed (BF); electrolytes at 50% (E50), 100% (E100) and 150% (E150) and betaine in water, or electrolytes at 100% for 36 h (E100 + 36 h) before processing at Day 42 of age.

L-DEB, low-DEB diet; H-DEB, high-DEB diet; Control, water alone; BF, betaine in feed; E50, E100 and E150, electrolyte solutions + betaine in water; E100 + 36 h, electrolyte solution + betaine in water for 36 h before processing.

Treatments repeated for birds in both L-DEB and H-DEB diets.

The significant (P = 0.019) relationship between CAD and LWG is shown in Fig. 2. The highest predicted LWG (61.7 g/day) was achieved at an CAD of 48, with a range of 44–54 supporting LWG of between 61.0 and 61.7 g/day.

Fig. 2.

The relationship between CAD (cation–anion difference, mEq) and LWG (g/day) for Pekin Ducks exposed to high ambient temperature for 9 h/day at 36–41 days of age and provided with either water, betaine in the feed (BF), one of three water electrolyte supplements (E50, E100, E150) and betaine for all days, or a water electrolyte (E100 + 36 h) and betaine supplement for 36 h before processing on Day 42 of age.

Discussion

High temperature reduces performance of meat chickens and, depending on severity, affects LWG, FI and feed efficiency (Lara and Rostagno 2013; Liu et al. 2020). Similar temperature challenges affect duck performance (Sun et al. 2019; Downing 2022), although there is much less research evidence. On the basis of the THI categories of Moraes et al. (2008), birds in the current study were likely to be suffering ‘severe discomfort’ and the reduced LWG during the high-temperature challenge over D36–41 would support this degree of stress. Previous performance of the same duck strain under thermoneutral conditions, raised as mixed sexes and in the same housing as used in the current study, was 73.7 g/day (84.9 g/day for males, 62.9 g/day for females; Downing 2010). This suggests that the high-temperature challenge depressed LWG in the control L-DEB-fed birds by ~38% and in control H-DEB-fed birds by 21%. At 20°C, LWG of Pekin ducks was 85.6 ± 2.5 g/day and at 30°C it was 59.4 ± 7.5 g/day, and this was a 31% reduction (Sun et al. 2019). Depending on the DEB diet and the shed temperature, it was comparable to LWG losses observed in the current study.

The optimal DEB varies according to a range of factors, but high temperature and the duration have a major influence (Ahmad and Sarwar 2006; Mushtaq et al. 2007, 2013). For meat chickens, under thermo-neutral conditions, a DEB of 200–270 mEq/kg has often been quoted as suitable (Borges et al. 2004; Szabó et al. 2011; Arantes et al. 2013; Popoola et al. 2020b). In the present study, over D15–35, under thermo-neutral conditions, ducks fed the diets with DEB of 160 and 217 mEq/kg had similar performance. For ducks, grower diets with a lower DEB could be more ideal because wet litter is a major management concern for duck producers (Karcher et al. 2013; Mushtaq et al. 2013). Borges et al. (2003) found that litter moisture increased linearly with DEB, as did also Ahmad et al. (2009). At DEB of 375 mEq/kg, excreta moisture content has been shown to be 81.2%, compared with 73.1% when the DEB is 150 mEq/kg (Ravindran et al. 2008). It is possible that the salts used, sodium especially, may have more influence than the absolute DEB value on litter moisture content (Mushtaq et al. 2013).

The control birds on the L-DEB diet had a 28% lower LWG over D36–41 than did control birds on the H-DEB diet, suggesting that the additional need for electrolytes under high temperature could, at least in part, be met by a diet with a higher DEB. During persistent periods of high temperature, meat birds pant and the physiological changes increase the loss of electrolyte ions, which causes acid–base imbalance (Borges et al. 2007). An obvious strategy to replace this loss would be to increase DEB. However, often the research supporting this concept has been less than convincing. Under tropical conditions (temperature ranged 26.1–37.5°C), bird performance was poorer when the DEB was 0 and 350 mEq/kg than when it was 50, and 250 mEq/kg (Ahmad et al. 2009). At a high temperature, a range of 150–250 mEq/kg was found suitable by Ahmad et al. (2009). At 29–34°C, feeding diets with DEB of 120, 220 and 320 mEq/kg to ‘finisher’ meat birds has been shown to support equivalent growth performance (Saki et al. 2016). Under thermo-neutral conditions, a DEB of 240 mEq/kg has been shown to support better performance than when the DEB is 40 and 340 mEq/kg, but the DEB had no effect when birds experienced high ambient temperature (Borges et al. 2003).

During the high-temperature challenge, for birds on the L-DEB diet, all electrolyte supplements increased LWG compared with the control birds. The highest LWG was achieved by suppling E100, E150 and E100 + 36 h supplements. For birds on the H-DEB diet, except for the E50 supplement, all other supplements supported LWG being equivalent to that of the control birds. On the E50 supplement, LWG was highest but equivalent to that of birds on the E100 + 36 h supplement. Betaine increased the LWG for birds on the L-DEB diet but had no effect on the LWG of birds fed the H-DEB diet. Together, these observations suggested that the effect of the supplementary treatments on LWG might be associated with the total electrolyte intake. This prompted an investigation of the relationship between LWG and the CAD, with CAD being the difference between the intake of cations (Na⁺ + K⁺) and the Cl⁻ ion concentrations. This relationship was found to be quadratic with the predicated maximum LWG being achieved when the CAD ranged from 44 to 55 mEq/day. The maximum LWG for birds on the L-DEB was observed when supplemented with E150 and a CAD of 54.5, while on the H-DEB diet, the maximum LWG was observed when birds were supplemented with E50 and a CAD of 44.3.

On the L-DEB diet, the betaine feed supplement supported a higher LWG than for the control birds, while the CAD was not different between these treatments (27.6 vs 27.0 mEq/day). However, on the H-DEB diet, the betaine feed supplement had no effect on LWG compared with the control treatment, with these treatments again having a similar CAD intake (37.0 vs 36.3 mEq/day), but the CAD values were ~10 mEq/day higher than for the same treatments on the L-DEB diet. The betaine effect may depend on the CAD intake, with a benefit when it is low and minimal benefit when high.

While exposure to high temperature increases water intake (Donkoh 1989; Lott 1991; Sayed and Downing 2011; Mushtaq et al. 2013), there is also an effect of electrolyte supplement. Birds supplemented with E100 and E150 consumed ~10% and 18% more water respectively, than did the control birds. The effect of electrolyte supplement is well supported by the differences recorded for birds supplemented with E100 for 36 h (E100 + 36) prior to farm pick-up for processing. In the first 4.5 days of high temperature, the average water intake was 816 mL/day and in the 36 h of supplementation prior to farm pick-up for processing it was 1106 mL/day.

The average LWG was determined over 6 days of high temperature. This equated to a total of 370 g and 368 g for the E100 + 36 h and E100 treatments respectively. The limited supplementary period of treatment E100 + 36 h could mean that total LWG of birds on the E100 + 36 h was related to increased hydration rather than greater tissue mass. During high temperature, the water intake and its retention were higher in meat chickens given water electrolyte supplements than those on tap water alone (Sayed and Downing 2011). The effect of electrolytes on LWG during high temperature might be limited and not continuous. During exposure to high temperature, electrolyte supplementation over D32–42 of age has been found to support higher LWG over the first 5 days (D32–36), but no further improvement in LWG was observed over the final 6 days (D37–42) of supplementation (Sayed and Downing 2011).

The higher water intake in birds provided electrolytes could, in some manner, reduce the stress birds experience during high temperature. The heterophil to lymphocyte ratio (H:L) has been identified as a measure of stress in poultry (Zulkifli and Siegel 1995; Puvadolpirod and Thaxton 2000). HS in meat chickens increases the H:L ratio (Yalçin et al. 2003; Borges et al. 2004; Gu et al. 2012; Barreto Sánchez et al. 2022). During high temperature, meat chickens supplied with electrolyte supplements have been shown to have a lower H:L ratio, suggesting that they experience less stress (Sayed and Downing 2011). The higher water intake in birds provided electrolytes could, in some manner, reduce stress. High temperature exposure decreases whole-blood viscosity (Zhou et al. 1998), which is likely to alter the peripheral resistance and reduce blood circulation to heat-exchange skin surfaces (Zhou et al. 1999a). Higher water intake increases blood and plasma volume and reduces whole-blood viscosity (Zhou et al. 1999a, 1999b). Under high temperature, an increased water intake acts as a heat sink and is associated with higher evaporative heat load and reduced respiration rate, all supporting higher respiratory efficiency (Belay and Teeter 1993). These same researchers also reported that supplementing water with 0.75% KCl increased water intake and the evaporative heat load and apparent respiratory efficiency. In the current study, the increased water intake could increase blood viscosity, but there is likely a limit to the benefit, depending on the temperature challenge. Whole-blood viscosity has been shown to increase as the temperature increases from 20°C to 25°C, with no further effect as the temperature increases to 30°C (Zhou et al. 1999b). Electrolyte supplementation will assist meat birds cope with HS at moderately high temperature effects (<30°C), but be less beneficial at a severely high temperature (>30°C); however, realistically, the severity depends not only on the absolute temperature but also the duration.

Betaine improves growth performance by regulating the osmotic pressure in animals under HS to prevent dehydration, maintain water content in cells, save energy and enhance nutrient bioavailability (Ratriyanto and Mosenthin 2018). Depending on the temperature conditions, betaine added to feed or water supports better performance in meat chickens and ducks (Wang et al. 2004; Zulkifli et al. 2004). In the current study, betaine had no effect on LWG over D15–35 of age under thermo-neutral conditions. During the high-temperature treatment period (D36–41), betaine in the feed increased LWG by 17.5% for birds on the L-DEB, with no effect when birds were fed the H-DEB diet, with no effects on FI or feed to gain. Under suitable temperature conditions, meat ducks supplemented with 0.5% betaine in feed had better performance (Wang et al. 2004). When meat ducks, 21–42 days of age, while exposed to cyclic high temperature (33–42°C for 6 h/day; 70% RH), were provided feed containing betaine at 0.7, 1.0 or 1.3 g/kg feed, betaine supported a 46–49% improvement in LWG, a 6.7–7.3% higher feed intake and a 9% better feed to gain ratio, with no differences among the different inclusion rates (Park and Kim 2017). Under these temperature conditions, betaine at 1.2 g/kg feed improved LWG by 4.3% and FCR by 15% (Park and Park 2017). Under the same high-temperature conditions, water supplementation with betaine at 0.4, 0.8 or 1.2 g/L on Days 22–42 of age increased duck FI by 4.8–5.5% and improved LWG by 9.8–15.7%, with the highest betaine dosage being superior to the lower doses (Shin et al. 2019). The betaine supplements increased blood electrolyte concentrations of sodium (Na⁺), potassium (K⁺), and chloride (Cl⁻) and this might be, in part, the way betaine supports duck performance under severe high-temperature stress (Shin et al. 2019). This might account for the differences seen in the current study where feed betaine improved LWG when birds were fed the L-DEB diet but not the H-DEB. The H-DEB diet would provide higher electrolyte intake because there were no differences in FI; however, there is a need to determine whether this increased blood electrolyte concentrations. The much higher response to betaine in the studies discussed above than in the current study is likely to be related to the severity of the stress imposed. The current results suggest that even under a moderate high-temperature stress, betaine in feed can be of benefit.

Neither the electrolyte supplement nor DEB had any effect on LW loss during transport and lairage, or on processed carcass weight. The supplements had no effect on the breast meat yield. High-temperature exposure can decrease breast yield in meat chickens (Smith 1993; Rosa et al. 2007; Zhang et al. 2012). The severity of the thermal challenge, the absolute temperature and duration, are factors affecting the performance and breast yield in meat chickens. Baziz et al. (1996) subjected meat chickens to constant temperatures of 22°C or 32°C over Weeks 4–7 of age and reported a depressed %breast weight to LW (11.9% vs 13.4%) at the higher temperature. Meat chickens exposed to a constant 34°C on Days 29–42 of age had a reduction in breast weight of 31.5%, while a cyclic temperature regime (23–36°C) reduced breast weight by only 9.9% (Zhang et al. 2012). In the current study, the lower maximum temperature, for a duration of 6 days, and the overnight recovery period limited the severity of thermal challenge compared with these earlier studies where a higher temperature range was imposed. The negative effects of high temperature on breast yields has been associated with reduced FI (Smith 1993; Lu et al. 2007; Rosa et al. 2007; Zhang et al. 2012). In the current study, there was no effect on feed intake.

Conclusions

Under the high-temperature challenge that can be considered to cause moderately severe HS conditions, providing water supplemented with electrolytes and betaine improved LWG. The requirement for increased electrolytes can be partly met by increased DEB. There is evidence that, at least in part, some of the benefit can be attributed to increased water intake. It is proposed that the intake of electrolytes is likely to be even more relevant under more extreme high temperatures, but this needs further evaluation.