The effect of dietary potassium and sodium on performance , carcass traits , and nitrogen balance and excreta moisture in broiler chicken *

The aim of the 3 × 3 factorial experiment on broilers was to investigate the effect of high dietary levels of potassium (K) and different levels of sodium (Na) on chicken performance, carcass traits, dry matter content in excreta and nitrogen balance. Three hundred and sixty one-day-old Ross 308 chickens were allocated to 9 groups, in 5 replicates of 8 (4♂ and 4♀). Chickens from 1 to 42 days old were kept in cages with wire floors to enable excreta collection, and were provided with water and feed ad libitum. The basal starter (days 1-14) and grower (days15-42) diets contained, as analysed, 1.73 g and 1.89 g·kg-1 chloride (Cl), 10.7 g and 10.8 g K and 0.69 and 0.94 g Na, respectively. Basal diets were supplemented with cations containing, as analysed, 12.2/11.8 g and 12.7/12.5 g·kg-1 K and 1.22/1.25 g and 1.68/1.61 g·kg-1 Na, for the starter/grower periods of feeding, respectively. The molar proportion of Na:K in diets used in the experiment ranged from 0.09 to 0.27 in the starter diet and from 0.13 to 0.25 in the grower/finisher diet; the dietary electrolyte balance (DEB) values varied between 255 to 349 and 264 to 336, respectively. During the starter feeding period, body weight gain (BWG), feed intake (FI) and feed conversion ratio (FCR) in the chickens were positively affected by increasing the Na supplement. Throughout the feeding period, Na supplementation improved BWG, FI and FCR and production index values and increased carcass yield. The dry matter content of the excreta was negatively affected by the K level in the diet; the 12.7 g K dietary content, in particular, caused a higher moisture content. 245 KORELESKI J. ET AL. The daily intake of nitrogen and nitrogen excretion grew when the dietary Na level was increased from 0.94 to 1.25 or 1.61 g·kg-1. The proportion of N retained to N intake decreased significantly when the dietary level of Na reached 1.61 g·kg-1, as compared to the proportion at a level of 0.94 g Na·kg-1. Interaction between dietary Na and K levels for BWG and other indices of performance, and for nitrogen utilization, confirm a dietary reciprocal relationship for both electrolytes.


INTRODUCTION
Broiler diets based on plant components usually contain more potassium than diets including animal originated by-products.This is a result of high K content of plant protein sources and prohibited meat meals in feeding of poultry.NRC (1994) requirements for K in broilers are 3.0 g•kg -1 for both periods of feeding.More recently, the requirements for K in chickens for the periods of 8-21 and 22-42 days old are for a body weight gain of 6.28 and 7.14 g .kg -1 , respectively (Oliveira et al., 2005).Plant diets which markedly exceeded these levels of K may change the dietary electrolyte balance (DEB) and increase water intake and excreta moisture (Vieira and Lima, 2005).According to Mongin (1981), the DEB value, i.e. the difference between the sum of positive cations (Na + + K + ) and negative anion (Cl -) equivalents, in the diet is of great importance at high ambient temperature and as regards the heat stress undergone by chickens in hot parts of the world.Even in moderate climates however, there may well be several weeks of very hot weather each year.The Mongin electrolyte balance refers to dietary K + , Na + and Cl -at levels covering the nutritional requirements for chicken.It is not unlikely however that at a K content much higher than required in the diet, excreta humidity prevention and correction of DEB values may complicate reciprocal electrolyte proportions.
For diets with a higher content of K, a question could be posed regarding the required levels of Na and Cl.Using Cl adequate diets, Johnson and Karunajeewa (1985) found that for optimum growth rate equivalents, the Na:K ratio in the broiler diet should not be allowed to fall below 0.5, or to rise above 1.8.This paper investigates chicken performance, slaughter indices, dry matter content in excreta, and nitrogen balance (in order to confirm the performance and slaughter indices) in broilers fed high K and Na supplemented plant diets with a moderate and constant Cl content.The very low or adequate content of Na gives dietary electrolyte balance values from 255 to 349.The molar Na:K ratio in this study fell to 0.09-0.27,markedly below levels recommended by Johnson and Karunajeewa (1985) because of high dietary K content.

MATERIAL AND METHODS
The Local Krakow Ethics Committee for Experiments with Animals approved all experimental procedures relating to the use of live animals.The trial was conducted during summer time with 360 Ross 308 broiler chickens of initial 40 g average body weight allocated to 9 groups in 5 replicates of 8 (4♂ and 4♀).Chickens from 1 to 42 days old were kept in cages with wire floors to enable excreta collection and were provided with water and feed ad libitum.
During the first 5 days of the chickens' 4 th week the feed consumed was measured and a total collection of excreta on droppings trays from 5 replicates of 8 chickens in each group was carried out.Feathers were removed from excreta trays and the excreta was weighted each day and stored at -20 o C. At the end of balance estimation, after thawing, the excreta were weighted again, homogenized and representative samples for the analysis of nitrogen content were taken.N contents in diets and in excreta were estimated by the Kjeldahl method (AOAC, 1990), using Kjeltec Auto 1030, Tecator.N-balance indices were calculated taking into account amounts of N ingested and N excreted (Becker and Harnish, 1958).
At the end of the experiment and after 12 h of starvation all chickens were weighed and 4 representative cockerels and 4 hens were chosen from each group with live body weights close to the group average, marked with number signs and decapitated.Chickens were ploughed, the intestines and crop were removed and carcasses stored overnight in 4 o C. The mass of the cooled carcasses with edible giblets (gizzard, liver, heart) were estimated and carcass yield calculated (Ziołecki and Doruchowski, 1989).The breast muscles and abdominal fat and livers and hearts were excised and weighted.The breast muscles and abdominal fat contents were expressed as % in carcass.The relative weight of liver and heart as % of liveweight were calculated.
The data were subjected to a two-way factorial analysis of variance.The significance of differences between means was determined by Duncan's multiple range test and differences were considered significant at P≤0.05.Statistical analyses were performed using Statistica 5.0 PL software (Statsoft Inc.).

RESULTS
As compared to broiler requirements, the dietary Na levels used in this experiment (Tables 1 and 2) were very low (Na + VL), low (Na + L) or adequate (Na + A).
During the starter feeding period, the BWG, FI and FCR in chickens were positively affected by increasing the Na supplement (P≤0.001),whereas the effect on performance of increasing the K level in the diet was small and statistically not significant (Table 3).Similar effects were observed in the grower feeding period (Table 3), but at that time, the increasing level of K significantly decreased the chicken's BWG.The experimental factors had no effect on the mortality throughout the feeding period (Table 3), but Na supplementation improved BWG, FI, FCR and PI values (P≤0.001).Significant interaction (P≤0.001) may confirm the relation of K and Na dietary level in the case of BWG and feed intake.The highest BWG values, the largest FI and the best FCR in the first feeding period were observed in chickens fed diets containing higher K + , Na + L and Na + A content and with DEB values from 329 to 336 (Table 2).The molar proportion of Na:K in the diets used in the experiment ranged from 0.09 to 0.27 in the starter diet and from 0.13 to 0.25 in the grower/finisher one.The DM content of excreta (Table 4) was negatively affected by the K level in the diet; in particular, the highest dietary K + content increased moisture content (P≤0.001).In contrast, Na supplementation had no effect on the dry matter content of excreta, but gives and increased carcass yield (P<0.05) in chickens (Table 5).A statistically unconfirmed tendency for a positive effect on carcass yield was also found in the case of added K. Dietary levels of K + and Na + had no significant effect on breast meat yield, abdominal fat content in the carcass and relative weights of liver and heart (Table 5).In balance estimations, the daily intake of nitrogen grew when the dietary Na level was increased from 0.94 to 1.61 g•kg -1 .Nitrogen excretion grew in a manner corresponding to the Na intake (P<0.05).The proportion of N retained N intake markedly decreased (P<0.05) when the dietary level of Na reached 1.61 g •kg -1 , as compared to the proportion at Na level of 0.94 g•kg -1 of diet (Table 6) to manner corresponding to the Na intake (P<0.05).The proportion of N retained to N intake markedly decreased (P<0.05) when the dietary level of Na reached 1.61 g•kg-1, as compared to the proportion at Na level of 0.94 g•kg-1 of diet (Table 6).

DISCUSSION
Electrolyte requirements and performance.For the first period of feeding, NRC (1994) recommends 3.0 g K and 2.0 g Na and 2.0 g Cl per kg of diet.For best weight gain and feed conversion, Borges et al. (2007) have suggested a requirement of 3.5 g Na and 3.66 g•Cl•kg -1 as recommended values at 7.45 g•kg -1 K and at a value of 240 mEq/kg (DEB), irrespective of ambient temperature.In contrast, Murakami et al. (1997) suggested that, at K 10.1 g•kg -1 , Na requirements were no more than 2.0 g up to 21 days old chickens.
In an experiment reported by Borgatti et al. (2004), a high weight gain was found at 1.8 g•Na + , 12.2 g•K + and 2.2 g•Cl • kg -1 of diet and at a DEB value of 330.In our experiment the highest BWG values, the largest FI and the best FCR in the first feeding period were observed in chickens fed diets containing higher K + (12.2 and 12.7 g•kg -1 ), Na + L and Na + A (1.22 and 1.68 g•kg -1 ) content and with DEB values from 329 to 349.
According to suggestions of specific cation effects independent of DEB (Johnson and Karunajeewa, 1985), the Na:K molar ratios in the diets used in our experiment were generally low.In diets with a high level of K, that ratio for adequate BWG in chickens reached values at 0.16 to 0.27 and 0.17 to 0.25, for FCR 0.16 to 0.19 and 0.17 to 0.20 in the first and second feeding periods, respectively.The values presented fall much lower than the 0.5 Na:K ratio established as a minimum for growth in Johnson and Karunajeewa (1985) experiment.This could suggest that in high K and Cl-adequate diets, the Na:K ratio may be markedly lower for effective chicken performance in first period of feeding.The poor performance for the Na + VL diet may confirm the Na deficiency status of a low Na diet for chickens.
In the second feeding period Murakami et al. (1997Murakami et al. ( , 2001) ) have suggested the requirement for chicken as being 1.5 g Na and 2.3 g Cl•kg -1 at a DEB of between 249-261 mEq/kg and a K level of 9.6 g•kg -1 .NRC (1994) recommends 1.5 g Na + ; 3.0 g•K + and 1.5 g Cl -•kg -1 of diet.For older broiler chickens, Borges et al. (2007) have found 3.5 g•Na + ; 6.66 g•K + and 2.94 g•Cl -kg -1 give the best weight gain and feed conversion in the tropics.Oliveira et al. (2005) estimated 6.3, 7.1 and 8.0 g of dietary K as a requirement for that macroelement to give broiler growth in the starter, grower and finisher feeding periods with a constant Na and Cl content in the diet.
The dietary Na levels in present experiment were very low (Na + VL), low (Na + L) or adequate (Na + A), as compared to broiler requirements (NRC, 1994;Murakami et al., 1997Murakami et al., , 2001;;Borges et al., 2007), whereas the dietary K levels used were relatively high (Oliveira et al., 2005).A significant improvement of BWG, FI and FCR was noted when the Na level in grower/finisher diet increased from 0.94 to 1.25 g•kg -1 .A further increase of Na level in the diet (to 1.6 g•kg -1 ) resulted in only a statistically unconfirmed tendency towards improved chicken performance.On the other hand, elevated dietary K level had a tendency to cause a deterioration in performance, but at 11.8 K and 1.61 Na, the BWG reached its highest value.Similar results were obtained across the entire period of the experiment (1-42 d).BWG and FCR values were significantly improved between chickens fed Na + VL and Na + L diets.If further elevation, from Na + L to Na + A, improved performance, this effect of Na was not significantly confirmed.Only in the case of FI was the effect of increasing the Na level to Na + A level significantly confirmed.Throughout the feeding period the poor performance for the Na + VL diet may confirm the Na deficiency status of a low Na diet (0.69-0.94 g•kg -1 ) for chickens fed high K level.
Carcass yield, nitrogen balance and excreta dry matter.Supplementing the diet with Na increased the carcass yield of the Na + L or adequate (Na + A) dietfed chickens, when compared to the Na + VL diet.A similar, but statistically unconfirmed, tendency was found in the case of added K.Both effects were probably the result of electrolyte influence on chicken performance and, above all, on body weight gain changes.
In the balance estimations presented in our experiment, the daily intake of nitrogen grew when the dietary Na + level increased from 0.94 g to 1.61 g•kg -1 .Being a result of feed intake changes and nitrogen intake, nitrogen excretion grew in a similar manner.Nitrogen retention was not, in fact, affected, but as compared to 0.94 g Na•kg -1 for the Na + VL diet, the proportion of N retained to N intake decreased when the dietary level of Na reached 1.61 g•kg -1 .This result seems to be in agreement with Adekunmisi and Robbins' (1987) findings that Na bicarbonate supplementation might stimulate uric acid excretion through the kidneys.
The comparison of BWG, carcass yield and non significant tendency in nitrogen retention and breast meat and abdominal fat content confirmed negative effect of 0.94 g•kg -1 Na content (Na+VL treatment) on organism when chickens fed high K levels.This is a sign of the deficiency of mineral component, among other important for process of nutrients absorption in the gut (McDowell, 1992).It can indicate a positive effect of enlarged dietary Na content to 1.25 g•kg -1 on growth and body composition and also, as a non significant tendency, on nitrogen retention.A positive effect of NaHCO 3 supplement to the diet on carcass weight and dressing percentage of chickens was reported by Ahmad et al. (2005).
Potassium may increase water intake and excreta moisture (Vieira and Lima, 2005) in broiler chickens.In our experiment, the K content in the basal non supplemented diet was relatively high and negatively affected the dry matter content of excreta.The K added to the basal diet increased that effect; in particular, a dietary 12.5-12.7 g•kg -1 decreased the dry matter content in excreta to 15-16 g•kg -1 , for both feeding periods.In layer diets, dietary K levels were elevated from 2.3 g to 20 g•kg -1 in the diet (Smith et al., 2000).They calculated that each 1 g increase of K caused a 1.2% increase of moisture content in excreta.
Among other factors that may affect litter moisture, increased water consumption is probably the primary one.Oviedo-Rondon et al. (2001) reported that, at higher levels of Na + in the diet, or given an excess of that electrolyte, Na might also increase litter moisture.In contrast, being at the lower limit of Na requirements for the diet (Na + VL), the Na levels used in our experiment did not affect the dry matter content in excreta.

CONCLUSIONS
The results of the experiment presented here suggest that at high level of K in the diet, and moderate level of Cl (1.73/1.89g•kg -1 ), the Na requirement for adequate chicken performance could be moderate and equal 1.2-1.7/1.25-1.6 g•kg -1 in the first/second period of feeding.Established Na requirement is the result of proportion between high dietary level of K and moderate level of Cl and is connected with the relatively high sum of cations and low Na:K ratio.Interaction between dietary Na and K levels for body weight gain and other indices of performance, and for nitrogen retention, suggest a reciprocal relationship between both electrolytes in the diet.

Table 2 .
Scheme of dietary electrolyte balance values DEB, mEq•kg -1 in diets

Table 3 .
The performance of chickens -in each period of feeding the values in the rows with different letters differ significantly (P≤0.05);x, y -values in the columns with different letters differ significantly (P≤0.05)

Table 6 .
Nitrogen balance -values in the rows with different letters differ significantly (P≤0.05)