Sodium and Chloride Requirements of Young Broiler Chickens Fed Corn-Soybean Diets (One to Twenty-One Days of Age)

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1 Sodium and Chloride Requirements of Young Broiler Chickens Fed Corn-Soybean Diets (One to Twenty-One Days of Age) E. O. Oviedo-Rondón, 1 A. E. Murakami,*,2 A. C. Furlan,* I. Moreira,* and M. Macari *Departamento de Zootecnia, Universidade Estadual de Maringá, Avenida Colombo, 5790, Maringá, Paraná, , Brazil; and Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista, Campus de Jaboticabal, São Paulo, , Brazil ABSTRACT Sodium (Na + ) and chloride (Cl ) nutritional plate in the proximal tibiotarsi decreased with Na + levels. requirements, dietary electrolyte balance (DEB), The TD incidence decreased with increases in dietary Na +. and their effects on acid-base balance, litter moisture, and Litter moisture increased linearly with sodium levels. In tibial dyschondroplasia (TD) incidence for young broiler Experiment 2, the Cl requirement was estimated as chickens were evaluated in two trials. One-day-old Cobb 0.25%. Chloride levels caused a quadratic effect (P 0.01) broilers were distributed in a completely randomized design with six treatments, five replicates, and 50 birds per on blood gas parameters, with an estimated equilibrium [blood base excess (BE) = 0] at 0.30% of dietary Cl.No experimental unit. Treatments used in both experiments were a basal diet with 0.10% Na + (Experiment 1) or Cl Cl treatment effects (P 0.05) were observed on litter (Experiment 2) supplemented to result in diets with Na + moisture or TD incidence. The best DEB for maximum or Cl levels of 0.10, 0.15, 0.20, 0.25, 0.30, or 0.35%, respectively. In Experiment 1, results indicated an optimum and 246 to 264 meq/kg in Experiment 2. We concluded performance was 298 to 315 meq/kg in Experiment 1 Na + requirement of 0.26%. Sodium levels caused a linear increase in arterial blood gas parameters, indicating an alkalogenic effect of Na +. The hypertrophic area of growth that the Na + and Cl requirements for optimum performance of young broiler chickens were 0.28 and 0.25%, respectively. (Key words: acid-base balance, chloride, sodium, tibial dyschondroplasia) 2001 Poultry Science 80: INTRODUCTION Sodium and Cl are minerals with important physiological functions. Optimum dietary balance of these minerals allows better chicken performance and may reduce leg problems. To determine nutritional requirements it is important to keep this balance. The NRC (1984) recommended a minimum requirement of 0.15% Na + and Cl for young broiler chickens. Britton (1991, 1992) concluded that to obtain the best body weight gain (BWG) the NaCl level should be 0.45%, or Na + at 0.20%, of the diet and the Cl requirement should be about 0.20%. The NRC (1994) has established requirements of 0.20% each for Na + and Cl for chicks 0 to 3 wk. These levels have been confirmed by Zanardo (1994). Butolo et al. (1995) verified the influence of NaCl levels on feed conversion ratio (FCR) and suggested a require Poultry Science Association, Inc. Received for publication December 27, Accepted for publication October 26, Present address: Department of Poultry Science, University of Arkansas, Fayetteville, AR To whom correspondence should be addressed: aemurakami@ uem.br. ment of 0.55% NaCl or 0.22% Na +. With the aim to verify broiler nutritional requirements from 1 to 21 d, Murakami et al. (1997b) estimated the best BWG with 0.25% of Na +. In another experiment, aiming to evaluate two sources and levels of Na +, Murakami et al. (1997a) estimated a requirement of 0.20% of Na + at 21 d. The same authors verified that there were no differences between sodium bicarbonate (NaHCO 3 ) and NaCl as Na + sources. Barros et al. (1998) estimated a nutritional requirement of 0.25% of Na + for male and for female broiler chickens from 1 to 21 d. Maiorka et al. (1998) determined a nutritional requirement of 0.30% Na + for maximum performance from 1 to 21 d of age. Interactions between Na +,K + and Cl have been evaluated in broiler diets (Melliere and Forbes, 1966; Johnson and Karunajeewa, 1985; Hooge, 1995, 1998). Dietary proportions of Na +,Cl, and K + determine dietary electrolyte balance (DEB) (Mongin, 1980). These electrolytes are essential in osmotic pressure regulation and acid-base balance. Excess Na + and K + promote increases in litter mois- Abbreviation Key: BE = blood base excess; BWG = body weight gain; DEB = dietary electrolyte balance; FCR = feed conversion ratio; FI = feed intake; TCO 2 = CO 2 tension; TD = tibial dyschondroplasia. 592

2 SODIUM AND CHLORIDE REQUIREMENTS FOR YOUNG BROILERS 593 ture, which could cause health and leg problems where the humidity is very high (Penz, 1988; Barros et al., 1998). Cation and anion imbalance affects chicken growth and could influence the incidence of leg problems (Nesheim et al., 1964; Leach and Nesheim, 1965, 1972; Karunajeewa and Bar, 1988; Teeter and Belay, 1995). Tibial dyschondroplasia (TD) incidence is increased with Cl excess not balanced with Na + or K + (Leach and Nesheim, 1972; Sauveur and Mongin, 1978; Ruíz-López et al., 1993). Many researchers have reported that an electrolyte balance of 150 to 350 meq/kg in commercial diets (1 to 21 d) guarantees a maximum growth rate and optimum bird performance (Teeter and Belay, 1995; Karunajeewa et al., 1986) and lower incidence of TD (Hulan et al., 1978). There are differences in experimental results, due to differences in mineral availability in commercial versus purified diets and influence of other minerals such as phosphorus and calcium (Johnson and Karunajeewa, 1985). Halley et al. (1987) observed a high correlation between TD and acid-base imbalance. This relationship indicates the effects of dietary mineral manipulation on blood buffer capacity, affecting functions such as bone mineralization. Because of the discrepancies in the estimates of Na + and Cl requirements for maximum performance and the lack of information that link these requirement levels with metabolism, leg disorders, and litter quality, in modern, fast-growing broiler strains, the purpose of this work was to re-evaluate Na + and Cl requirements of young broiler chickens, to determine the best DEB for obtaining maximum BWG and optimum FCR, and to observe metabolic influences in acid-base balance, TD incidence, and litter moisture. MATERIALS AND METHODS Two trials were completed; each used 1,500 1-d-old male Cobb broiler chickens. Birds were randomly housed in 30 pens (5.1 m 2 ), in an open-sided house with sidewall curtains, with 50 birds per pen. Fresh wood shavings were used as litter over concrete floors. A 350-watt infrared lamp was placed in each pen for initial heating of the birds. A continuous illumination program was used during the first week and then 20 h light:4 h darkness until slaughter. One tube feeder and one automatic water fount were available in each pen. Birds were provided the experimental mash diets and tap water for consumption ad libitum. Chickens were vaccinated against Marek s disease at the hatchery and against Newcastle and Gumboro diseases at 8 d of age. Diet chemical analyses were made according to procedures described by AOAC (1990). The Na + concentrations were determined by atomic absorption spectrophotometry; Cl was measured by AgNO 3 titration and K + by flame photometry. A tap water sample was analyzed to establish mineral composition of Na +,K +, and Cl. Results indicated a concentration of these electrolytes less than 0.5 mg/kg. Birds were weighed at the start and the end of the experiment, and feed consumption per pen was determined. Every bird that died or was removed was weighed; pen feed intake at that moment was recorded, and these data were used for correction of feed conversion. Average maximum and minimum environmental temperature in the house were recorded daily. To determine acid-base balance status, eight 2-mL blood samples per treatment were taken, by cardiac puncture anaerobically, at 15 d of age. Measurements were taken for blood ph, partial pressure of CO 2, partial pressure of O 2, bicarbonate (HCO 3 ), CO 2 tension (TCO 2 ), base excess (BE), and saturation of hemoglobin with oxygen. A minimum 80% and maximum 98% oxygen saturation was considered as a satisfactory sample. Body temperature of 42 C and 10.5 g/dl hemoglobin were used for device calibration (Ruíz-López and Austic, 1993). To evaluate TD incidence, two 22-d-old chickens per experimental unit (10 by treatment) were weighed and killed, and two methodologies were used: 1) the right leg was used for classification by scoring system of Edwards and Veltmann (1983); and 2) the left epiphysial tibias were fixed in Bouin solution for histological analysis (Becøak, 1976). Decalcification was made with Haug solution, to avoid bone tissue hydrolysis, and inclusion was done with paraffin. Cuts were made with a rotary microtome at 5 µm, and samples were stained with hematoxilineosin, for epiphysial disc zone observation and characterization of TD lesions. Three regions were considered: growth plate band, proliferating cartilage, and hypertrophic cartilage. Calcified cartilage was considered as the lower limit to determine the thick hypertrophic zone in TD diagnosis (Thorp et al., 1993). The data collected on TD, at gross dissection and after histological assessment, belong to a set of mutually exclusive and exhaustive categories (i.e., a score of two cannot be assumbed to be twice as bad as a score of one). Therefore, the analysis of variance applied directly to these FIGURE 1. Print screen of histological plates of tibial epiphysial discs of chickens used to calculate areas through image analyzer software (Image-Pro ). Normal bone (A), bone with tibial dyschondroplasia indicated (B), growth plate band and proliferating cartilage areas (A 1 ), hypertrophic area (A 2 ), and total area of epiphysial disc (A 3 ).

3 594 OVIEDO-RONDÓN ETAL. TABLE 1. Composition of experimental diets 1 Calculated sodium levels (%) (Experiment 1) 2 Calculated chloride levels (%) (Experiment 2) 2 Ingredient Ground yellow corn Soybean meal Dicalcium phosphate Limestone Soybean oil DL-Methionine 99% Lysine Premix 3, Antioxidant Sodium chloride NaHCO KCl Calculated analysis Mongin no., 5 meq/kg All diets were calculated to contain 22% of CP; 3,100 kcal/kg ME; 0.965% calcium; 0.45% available phosphorus; and 0.95% potassium. In Experiment 1, Cl was 0.20%, and in Experiment 2 Na + was 0.20%. The 0.20% Na + or Cl diets represent the NRC (1994) control treatments. 2 The determined levels of sodium (0.10 to 0.35%), chloride (0.10 to 0.35%), and potassium (0.95%) were in close agreement with the calculated levels. 3 Composition of vitamin premix (per kg of premix): vitamin A, 2,000,000 IU; cholecalciferol, 400,000 CIU; vitamin E, 5,000 IU; menadione sodium bisulfite, 600 mg; vitamin B 1, 400 mg; vitamin B 2, 1,200 mg; vitamin B 6, 800 mg; folic acid, 200 mg; nicotinic acid, 6,000 mg; biotine, 20 mg; calcium pantothenate, 2,400 mg; choline chloride, 52,000 mg; vitamin B 12, 3,000 mg; antioxidant (BHT), 19,600 mg; coccidiostat (nicarbazine), 100,000 mg; and growth promotor (zinc bacitracin), 10,000 mg. Supplied by Roche (São Paulo, Brazil). 4 Composition of mineral premix provided as follows per kilogram of premix: iron, 1,000,000 mg; manganese, 16,000 mg; zinc, 100,000 mg; copper, 20,000 mg; cobalt, 2,000 mg; selenium, 80 mg; and iodine, 2,000 mg. Supplied by Roche (São Paulo, Brazil). 5 Mongin number = (Na +, meq/kg + K +, meq/kg] Cl, meq/kg (Mongin, 1980). scores would violate assumptions about normality. Moreover, the cardinal numbering of the categories does not imply that the distance between categories is in any sense regular (McCullagh and Nelder, 1983). Because of this irregularity, a method was designed to measure tibia areas (continuous variable) with a software for image analysis (Image-Pro ). 3 For this process, 10 tibia histological plates by treatment were scanned. Three areas were measured: 1) growing cartilage (growth plate band and proliferating cartilage zones), 2) hypertrophic zone, and 3) total area of the epiphysis, including the chondro-epiphysis (Figure 1). These data were analyzed by generalized linear models (GLIM ) 4 (Nelder and Wedderman, 1972). Litter moisture score was evaluated at 20 d, using four subsamples by experimental unit. It ranged from a score of 1, a dry litter in good condition, to a score of 4, very damp litter. Average value was used to indicate litter score. Litter moisture percentage was determined by a process described in AOAC (1990). Experiment 1 In this experiment, the response to different levels of Na + was evaluated in 1 to 21-d-old chicken males. Means of maximum and minimum temperature were 23.6 ± 2.4 C and 15 ± 2.2 C. Initial bird weight was 41 ± 0.6 g. Six dietary treatments consisted of a basal diet deficient in Na + (0.10%), reformulated slightly for each diet to give 3 Media Cybernetics, LP 8484, Silver Spring, MD NAG, Inc., Downers Grove, IL University Estadual de Maringá, Maringá, PR Brazil. five supplementary levels of Na + (0.05, 0.10, 0.15, 0.20, or 0.25%) from NaHCO 3 (0.19 to 0.93%), resulting in six diets with total Na + levels of 0.10, 0.15, 0.20, 0.25, 0.30, or 0.35%. Diets (Table 1) were formulated to be isonutritive, including levels of about 0.95% of K + and 0.20% Cl, and satisfied recommendations of the NRC (1994), with alterations by genetic line requirements. Feedstuff composition was based on a methods by Rostagno et al. (1987) NRC (1994) and results of the Animal Nutrition Lab. 5 The DEB was calculated by the method of Mongin (1980) (DEB = [Na +, meq/kg + K +, meq/kg] Cl, meq/kg) (Table 1). The experimental design was completely randomized with six treatments, five replicates, and 50 birds by experimental unit. Statistical analyses were performed with an SAS (1998) software, by using ANOVA and mean separation with Tukey s multiple-range test. To estimate Na + requirement, quadratic, broken line, or both models were used. Response curves were fitted by linear and quadratic regression procedures using PROC REG of the GLM procedure of SAS (1998) software. Because of the low cost of these nutrients in feed formulation, and the best statistical fit of the quadratic models, these models were chosen to draw the conclusions. Some results of the broken line models are discussed. Experiment 2 This trial was conducted similarly to Experiment 1, differing in relationship to the mineral being studied; in this case, Cl rather than Na + was used in a dose response test. Average maximum and minimum temperatures were 24.7 ± 3.6 C and 18.4 ± 1.9 C, respectively. Initial chicken weight was 46 ± 0.9 g. Treatments consisted of a

4 SODIUM AND CHLORIDE REQUIREMENTS FOR YOUNG BROILERS 595 basal diet deficient in Cl, at 0.10%, supplemented with five levels of Cl (0.05, 0.10, 0.15, 0.20, or 0.25%) from NaCl (0.05 to 0.47%) and resulted in diets with total Cl levels of 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35%. Experimental diets (Table 1) were otherwise isonutritive. Measured variables, experimental design, and statistical analysis were similar to Experiment 1. Experiment 1 RESULTS AND DISCUSSION Sodium levels had a quadratic effect on BWG (P 0.001), feed intake (FI) (P 0.05) and FCR (P 0.01) (Table 2). The BWG and FI were maximized at 0.26 and 0.25% Cl, respectively, and the lowest FCR was estimated at 0.28% Cl. These values are similar to the requirement of 0.25% estimated by Barros et al. (1998) and Murakami et al. (1997b) and higher than those reported by Britton (1992), NRC (1994), and Murakami et al. (1997a), all of whom estimated a Na + requirement of 0.20%. Maiorka et al. (1998) concluded that 0.30% Na + in the diet was necessary to obtain the best performance. Their experiment, however, was accomplished in batteries, and the effects of higher levels of Na + might have had a different influence than was observed in our experiment on litter due to coprophagy and Na + recycling and perhaps more disease stress in the latter than in the first. Means of bird blood gas variables observed at the age of 15 d in Experiment 1 are shown in Table 3. A linear effect of Na + levels was observed on ph, HCO 3, TCO 2 (P 0.01), and BE (P 0.001). Dietary Na + has an indirect alkalogenic effect on acid-base balance as reported by Ruíz-López and Austic (1993) and discussed by Hooge (1998). The BE and ph were increased (P 0.01) at the highest level of Na + (0.35%) (Table 3), indicating a metabolic alkalosis, apparently not compensated (partial pressure of CO 2 without significant differences), which reduced bird performance (Table 2). As a result, we concluded that birds could be in acid-base balance with 0.30% total dietary Na + but not with 0.35% Na +. A linear increase (P 0.001) in litter moisture was noted due to increased dietary Na + levels (Table 4). Similar results were observed by Hurwitz et al. (1973), Damron et al. (1986), and Murakami et al. (1997a). Excessive Na + intake causes physiological effects such as increased water consumption, manure moisture, and urinary Na + excretion and significantly decreased kidney glomerular filtration ratio, regulated by variation in arginine-vasotocin secretion (Freeman, 1983; Vena et al., 1990). This effect explains why greater than 0.30% Na + in the diet increased litter moisture significatively when compared with other treatments (Table 5). At greater than 0.30% of Na +, there was a relative deficiency of Cl concentration in the blood and kidney, because Na + had not been offered only as NaCl. This deficiency caused an increase in transtubular potential at the distal tubule, increasing excretion of H + and K +. The final result was metabolic alkalosis due to plasma HCO + 3 regulation, TABLE 2. Performance of young broiler chickens (1 to 21 d of age) fed diets with different levels of sodium or chloride Total sodium or chloride levels (%) Mean SEM Equation r 2 Experiment 1 (sodium) Body weight gain, g 667 b 732 a 759 a 770 a 764 a 747 a Y ij = ,016.39X 3,837.40X Feed intake, g 1,064 1,115 1,117 1,122 1,124 1,098 1, Y ij = ,328X 2,701.55X Feed:gain ratio, g:g a ab b b b b Y ij = X X Experiment 2 (chloride) Body weight gain, g 734 b 795 a 813 a 819 a 822 a 812 a Y ij = ,607.47X 2,962.12X Feed intake, g 1,105 b 1,132 ab 1,154 a 1,165 a 1,166 a 1,166 a 1, Y ij = 1, ,548.78X Feed:gain ratio, g:g a b b b b b Y ij = X X a,b Means within a row lacking a common superscript differ significantly (Experiment 1, P < 0.001, body weight gain and feed conversion ratio; Experiment 2, P < 0.05, feed intake; P < 0.01, feed conversion ratio; and P < 0.001, body weight gain). 1 NRC (1994) control treatment.

5 596 OVIEDO-RONDÓN ETAL. TABLE 3. Arterial blood gas means of 15-d-old chickens fed diets containing different levels of sodium or chloride Experiment 1 (sodium) Experiment 2 (chloride) Variable 1 Mean 2 SEM Equation 3 r 2 Mean 2 SEM Equation 3 r 2 ph Y ij = X Y ij = X X PO 2, mm Hg NS NS PCO 2, mm Hg NS NS Bicarbonate, mm/l Y ij = X Y ij = X X TCO 2, mm/l Y ij = X Y ij = X X Base excess, meq/l Y ij = X Y ij = X X Oxygen saturation, % NS NS 1 PO 2 = Partial pressure of O 2 ;PCO 2 = partial pressure of CO 2 ;TCO 2 = CO 2 tension. 2 Average of all treatments. 3 Regression equations that describe data response in relation to the dietary treatments. which was dependent not only on the absolute ratio of H + excretion but also on the relative ratio between H + excretion and Cl reabsorbtion. If H + excretion increases, in relation to reabsorbtion of Cl, plasma HCO 3 + concentration will be also increased (Riella, 1988). No effect (P 0.05) of Na + levels on TD incidence was found with the methodology of Edwards and Veltmann (1983) (Table 4). Histological evaluation of tibia epiphysical areas, however, demonstrated that areas of growth cartilage (A 1 ) had a normal distribution and did not have significant differences (P 0.05) relative to dietary Na + levels but did have differences in chicken BWG (P 0.05), showing an allometric relation of these bone regions with the whole animal (r = 0.48). Hypertrophic (A 2 ) values were not normally distributed. We determined that these data could be plotted according to gamma distribution. A nonlinear model with link function inverse power had the best adjustment to data distribution in relation to Na + levels, which was the only significant factor to explain area variation. This model explains (P 0.05) a decrease in the tibia epiphysis hypertrophic area with increasing dietary Na + (Figure 2). The cartilage hypertrophic region is considered as the principal area affected in TD, therefore we concluded that TD incidence is reduced as the dietary Na + is increased by supplementation with NaHCO 3. This reduction could be related to the indirect alkalogenic effect of Na + observed from blood gas analysis (Table 3), which guarantees a better blood ph for bone neoformic activity of osteoclasts, starting from 0.25% of Na + (Simons et al., 1987; Carano et al., 1993). Based on this work, the dietary Na + requirement for the starter phase with about 0.95% K + and 0.20% Cl is around 0.28%. At this level, acid-base balance is normal, productive performance is optimal, and TD incidence is minimized. Experiment 2 A quadratic effect of Cl was observed on every variable measured (Table 2). Based on regression equations, it was estimated that 0.27 and 0.30% of Cl maximized BWG and FI, respectively, and 0.25% of Cl minimized FCR. These values are higher than those recommended by the NRC (1994), Rostagno et al. (1996), and Murakami et al. (1997b), all of whom recommended 0.20% Cl in the diet. However, using the broken line model, it was estimated that BWG (816 g) did not increase (P 0.01) above 0.17%, and FCR (1.426) did not improve above 0.15% dietary Cl. These values are lower than those recommended by the NRC (1994), Rostagno et al. (1996), and Murakami et al. (1997b). In the present experiment, the data were best TABLE 4. Litter moisture and tibial dyschondroplasia incidence of young broiler chickens Total sodium (%) or chloride (%) Mean SEM Equation r 2 Experiment 1 (sodium) Litter moisture (%) b ab b ab ab a Y ij = X 0.75 Litter score Y ij = X 0.75 Tibial dyschondroplasia NS 0.85 Experiment 2 (chloride) Litter moisture (%) NS Litter score NS Tibial dyschondroplasia NS a,b Means within a row lacking a common superscript differ significantly (P < 0.001). 1 NRC (1994) control treatment. 2 Litter moisture: 1 = Litter is dry to 4 = Litter is very damp. 3 Tibial dyschondroplasia score at 22 d of age by method of Edwards and Veltmann (1983); 0 = normal cartilage, without or slight irregularities; 1 = cartilage with some thickness or irregularity; 2 = thick cartilage; and 3 = large mass of cartilage not ossified.

6 SODIUM AND CHLORIDE REQUIREMENTS FOR YOUNG BROILERS 597 TABLE 5. Performance of young broiler chickens in function of dietary electrolyte balance (Mongin, 1980) Experiment 1 Experiment 2 Variables Equation r 2 DEB 1 Equation r 2 DEB 1 Body weight gain, g Y ij = X X Y ij = 1, X X Feed intake, g Y ij = X X Y ij = X Feed:gain ratio, g:g Y ij = X X Y ij = X X Dietary electrolyte balance = [Na + + K + ] Cl, meq/kg. fit by quadratic models for all of the variables studied. Quadratic models typically give higher estimates of nutrient requirements than broken line models, but the pattern of the data, to a great extent, determines which model is most relevant to a particular dataset. Arterial blood gas analysis (Table 3) showed a quadratic effect of Cl levels on ph, HCO 3, TCO 2 (P 0.01), and BE (P 0.001). These results disagree with observations by Adesina and Robbins (1987), Ruíz-López and Austic (1993), and Hooge (1998). These researchers reported that increased dietary Cl levels have an indirect acidogenic effect on bird metabolism. Although chickens showed this response up to 0.25% of dietary Cl in the present trial, there might have been some compensatory effects on acidosis that occurred in broilers fed diets with 0.30 and 0.35% Cl. Based on ph, HCO 3, and TCO 2 parameters, it was estimated that broiler chickens fed diets containing 0.20 to 0.30% Cl were in acid-base balance, which supported the best performance (Table 2). The results of litter moisture and TD incidence, by using the method of Edwards and Veltmann (1983), are given in Table 4. There was no effect (P 0.05) of dietary Cl on manure moisture and TD incidence. If Cl is in optimum relation to Na +, as in NaCl, no modifications of bird water balance will be observed (Freeman, 1983). When the three histological areas of tibia growing cartilage (Methodology 2) were analyzed, we observed that values of total areas of epiphysis (A 3 ) and the growth cartilage (A 1 ) showed normal distribution and correlation with body weight (r = 0.68), but the hypertrophic zone of cartilage (A 2 ) did not. Many nonlinear models were tested, but none could explain (P 0.05) data response in function of BWG parameters, litter moisture, and dietary Cl levels. In this experiment, metabolic acidosis was not observed with the maximum Cl level. Perhaps, if a higher dietary Cl had been used, with greater metabolic acidosis, it would have been possible to observe area increases of the hypertrophic cartilage region and consequently greater TD incidence. In Experiment 1, broilers showed the best performance (BWG, FI, and FCR), when the diet had a DEB between 298 and 315 meq/kg (Table 5). The best performance was observed when the diet had between 246 and 264 meq/ kg in the Experiment 2. Feed intake was reduced as a result of DEB decrease and higher dietary Cl levels. These results are in the optimum range for growing chickens recommended by Sauveur and Mongin (1978) and verified by other authors (Hooge, 1995, 1998). In conclusion, it is suggested that Na + and Cl requirements for optimum FCR of young broiler chickens are 0.28 and 0.25%, respectively, based on supplementation with NaHCO 3 for additional Na + or NaCl for additional Cl. The best DEB for the starter phase was between 246 and 315 meq/kg, under conditions of these tests. It was demonstrated that using approximately these dietary levels, acid-base balance is normal, and TD incidence is minimized. However, lower levels of Na + appear to increase TD incidence. Litter moisture increases linearly as dietary Na + increases, even though dietary Cl has no effect on this variable. REFERENCES FIGURE 2. Nonlinear model (gamma distribution and link function inverse power) describing areas of hypertrophic region of tibial growing cartilage of broiler chickens in relation to dietary sodium levels at 22 d of age. Supplemental sodium (0.05 to 0.25%) was provided from sodium bicarbonate (0.19 to 0.93%). Adesina, A. A., and K. R. Robbins, Effect of dietary electrolyte balance on growth and metabolic acid-base status of chicks. Nutr. Res. 7: Association of Official Analytical Chemists, Official Methods of Analysis. 15th ed. Association of Official Analytical Chemists, Arlington, VA. Barros, J.M.S., P. C. Gomes, L.F.T. Albino, and A. H. Nascimento, Sodium levels over performance parameters of broiler chickens from 1 to 21 days of age. Page 14 in: Anais da Conferência APINCO 98 de Ciência e Tecnologia Avícolas. FACTA, Campinas, SP, Brazil. Becøak, W.P.J., Cytology and Histology Technics. Livros Técnicos e Científicos S.A., Rio de Janeiro, RJ, Brazil. Britton, W. M., NaCl for broiler chick growth. Poultry Sci. 70:1 18. Britton, W. M., Dietary sodium and chloride for maximum broiler growth. Zootecn. Int. 1:52 57.

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