Semana de Idade
ABSTRACT
Tw o experim ent s w ere carried out using 712 day-old chicks t o evaluate the electrolytic balance (Na+K-Cl) in pre-starter (1-7 days) broiler diets. The feed, based on corn and soybean meal w ith 21.5 % protein and 2,900 kcal M E/kg, w as offered ad libitum. In experiment I, K level w as fixed, and Na and Cl levels w ere changed, using four treatments and eight replicates of 16 birds. In experiment II, increasing levels of Na and K w ere used, w ith a total of four treatments and five repetitions of 10 birds. In both experiments, the dietary electrolytic balance w as 40; 140; 240 and 340 mEq/kg. Electrolytic balance caused a quadratic effect on w eight gain and feed:gain ratio, and a linear increase in feed intake w h en t h e el ect r o l yt i c b al an ce w as i n cr eased b y t h e si n g l e supplementation of Na, indicating that this ion stimulates feed intake of birds at this stage. How ever, feed intake w as maximum for 202 mEq/ kg, w hen K and Na levels w ere concurrent ly increased in t he diet , indicating that there is a limit over w hich feed intake is depressed as a f unct ion of excessive K. The ideal elect rolyt ic diet ary balance w as betw een 246 and 277 mEq/kg, obtained by the manipulation of Na and Cl levels.
RESUM O
Foram conduzidos dois experimentos, utilizando-se 712 pintos de corte para avaliar o efeito do balanço eletrolítico (Na+K-Cl) em rações pré-iniciais (1-7 dias) de frangos de corte. As rações à base de milho e farelo de soja, com 21,5 % de proteína e 2.900 kcal EM /kg, foram oferecidas à vontade. No experimento I, o nível de K foi fixado e os níveis de Na e Cl foram manipulados, em 4 tratamentos com 8 repetições de 16 aves cada. No experimento II, níveis mais elevados de Na e K foram usados, com 4 t rat am ent os e 5 repet ições de 10 aves cada. Em am bos os experimentos, os balanços eletrolíticos foram de 40; 140; 240 e 340 mEq/kg de ração. O balanço eletrolítico causou um efeito quadrático no ganho de peso e na conversão alimentar e um aumento linear no consumo de alimento quando o balanço eletrolítico foi aumentado pela suplementação de Na, indicando que esse íon estimula o consumo de alimento das aves nesse período. Porém, o consumo de alimento foi m áxim o em 2 0 2 m Eq / k g , q u an d o o s n íveis d e K e Na f o r am simultaneamente aumentados na dieta, indicando que o limite superior de consumo de alimento é deprimido em função do K em excesso. O balanço elet rolít ico ideal f oi ent re 246 e 277 m Eq/kg obt idos pela manipulação dos níveis de Na e Cl.
0121 Código / CodeCodeCodeCodeCode
Ana Vitória Fischer da Silva
Depto. de Fisiologia - UFPR / SCB Caixa Postal 19031
Centro Politécnico - Jd. das Américas 81531-990 - Curitiba – PR - Brasil
E-mail: avit oria@bio.uf pr.br Correspondência / M ail Address
Unit erm os / Keyw ords
cloro, eletrólitos, frangos, potássio, sódio
b ro ilers, ch lo rin e, elect ro lyt es, p o t assiu m , sodium
Borges SA1
M aiorka A1
Laurentiz AC1
Fischer da Silva AV 2
Santin E1
Ariki J1
1-FCAV / Unesp, Jaboticabal
2- Depto. de Fisiologia - Universidade Federal do Paraná, Curitiba
INTRODUCTION
Nut rit ional programs using pre-st art er diet s have been ext ensively discussed in t he last decade. The adopt ion of t his pract ice is just if ied as t he bird has dist inct ive nut rit ional needs at t his st age. On t he ot her hand, it is hard t o f ind inf ormat ion in lit erat ure on t he elect rolyt ic balance of broilers up t o 7 days o f ag e. Th e essen t i al el ect r o l yt es f o r t h e maint enance of t he osmot ic pressure and acid-base b alan ce ar e so d iu m (Na+), p o t assiu m (K+)an d
ch lo r in e (Cl-). Besid es t h eir n eed in m in im u m
am o u n t s in t h e f eed t o sat isf y t h e n u t rit io n al requirement s, it is import ant t o maint ain t he proper balance among t hem. The availabilit y of t heses ions m ay be inf luenced by t he int est inal and kidney hom eost asis regulat ion, as a result of increased absorpt ion or excret ion. M ongin & Sauveur (1977) concluded t hat t he elect rolyt ic balance of t he diet can be summarized by t he equat ion Na++ K+ - Cl-,
w hich value expresses t he am ount and t he rat io among t hese ions. These aut hors proposed t he ideal value of 250 mEq/kg or 25 mEq /100g in broiler diets. M aiorka et al. (1998) f ound a value of 160 mEq/kg; how ever, Borges et al. (1999) suggest ed t he balance of 251 mEq/kg in pre-st art er diet s, Rondón et al. (2000), evaluat ing t he perf ormance of broiler up t o 7 days of age, f ound values w hich varied bet w een 250 and 319 mEq/kg f or w eight gain and f eed:gain rat io, respect ively. The experiment s of t he present st udy aimed t o det ermine t he best elect rolyt ic rat io (Na+K-Cl) in pre-st art er diet s f or chicks up t o seven days of age.
M ATERIALS AND M ETHODS
Seven hundred and t w elve male day-old chicks w as used in tw o experiments. The birds received diets based on corn and soybean meal ad libitum w ith 21.5 % protein and 2,900 kcal EM /kg, and the levels of t he ot her nut rient s w ere added according t o t he National Research Council - NRC (1994). Feedstuffs samples w ere taken to be analyzed for Na, K and Cl content. Water samples w ere also analyzed for the sam e m i n er al s. So d i u m an d p o t assi u m w er e det erm ined by f lam e spect rophot om et er (AOAC, 1990) and chlorine by AgNO titration (Lacroix et al.,
and 340 mEq/kg of f eed) and eight replicat es. The K level remained const ant (Table 1), w hereas Na and Cl levels w ere alt ered t o obt ain t he desired elect rolyt ic balance. In Experiment II, t he birds (Ross st rain) w ere dist ribut ed in bat t eries w it h 10 birds per experiment al unit in a complet ely random experiment al design w it h f our t reat ment s (40, 140, 240 and 340 mEq/kg of f eed) and f ive replicat es. Na and K w ere added at increasing levels (Table 1), and t he calculat ed elect rolyt ic balance “ M ongin Number” w ere obt ained by t he addit ion of d e NaCl, NaHCO3, KHCO3 an d NH4Cl in t h e f eed . M axim um and m inim um t em perat ures, and relat ive humidit y w ere monit ored daily. Wat er t emperat ure and p H w ere reco rd ed t w ice a d ay, at t h e lo w est an d highest t em perat ure hours. W eight gain (W G), f eed int ake (FI) and f eed:gain rat io (F:G) w ere evaluat ed. The result s w ere submit t ed t o analysis of regression and, w hen necessary, t he means w ere compared by t he t est of Tukey.
RESULTS AND DISCUSSION
From 1 to 7 days of age, a quadratic effect (p<0,05) w as observed for w eight gain and feed:gain ratio, and to feed intake and w eight gain in Experiments I and II, respect ively (Figures 1 and 2), and t he result s w ere d ep en d en t o n t h e elect r o lyt es u sed t o alt er t h e electrolytic balance. The ideal Na+K-Cl ratio for w eight gain and feed:gain w as betw een 277 and 246 mEq/kg, w hen K w as fixed. When K and Na w ere increased, the ratio w as 227 mEq for w eight gain.
The comparison of means of the treatments (Table 2) allow s us to infer that special attention must be paid to high Cl levels in t he f eed (0.77% ), as w ell t o low elect rolyt ic balance (40 m Eq), w hich should not be recommended to birds at this stage. This is explained by the fact that excessive amounts of Cl and low or negative elect rolyt ic balance in t he f eed m ay reduce t he pH, promoting metabolic acidosis (Johnson & Karunajeew a, 1985; Ruiz-Lopez & Austic, 1993), show ing the direct or indirect negative effect of the excess of Cl.
w eight gain, corroborating the results of Johnson & Karunajeew a (1985) and Borges et al. (1999). It is possible t hat K levels (0.95 e 1.05% ) m ay have exceed ed t h e b ird s t o leran ce, as t h e est im at ed requirement of this ion is 0.30% (NRC, 1994). The results obtained w ith increasing Na supplementation, specially the linear response in feed intake, suggest that Na requirements are underestimated, and the performance obtained w ith low electrolytic balance, due to the addition of high Cl levels, show s that high levels of Cl should be avoided.
When the electrolytic balance (Na + K - Cl) w as higher or low er than 240 mEq, bird performance w as impaired, corroborat ing t he hypot hesis t hat w hen acid-base balance is deviated from homeostasis to alkalosis or acidosis, m et abolic pat hw ays m ay be alt ered, and are m ore involved in regulat ion of homeostasis than in animal grow th (M ongin, 1981).
Th e averag e en viro n m en t al t em p erat u re an d relat ive humidit y f luct uat ed bet w een 28 - 32ºC and 51% , 23 - 34ºC and 74% , and w at er t emperat ure w as bet w een 19 t o 29ºC w it h pH of 7.15 and 21 t o 25oC w it h p H o f 7 .0 0 , in Exp erim en t s I an d II,
respect ively. Analysis of t he t ap w at er indicat ed t hat it cont ained 0.7 ppm Na and t races of K and Cl. Alt hough w at er int ake w as not evaluat ed, previous st udies show ed a linear increase in w at er int ake as t he elect rolyt ic rat io increased in t he diet (Borges et al., 1999). Diet s w it h higher levels of elect rolyt es can in crease b lo o d o sm o larit y, sp ecially in t h e
presence of Na. This is import ant because an increase in w at er int ake m ay st im ulat e f eed int ake. Despit e previous st udies had show n t hat KCl, NaHCO3 and NaCl sig n if ican t ly in crease w at er in t ak e (Bo rg es, 1 9 9 7 ; Borges et al., 1998) in grow ing and f inishing st ages, Borges et al. (1999) f ound t hat diet s w it h high levels of Cl and/or K did not stimulate w ater intake during the first seven days of age.
The consequence of a higher w ater intake promoted by diet s w it h high elect rolyt ic balance is higher lit t er humidity. How ever, M aiorka et al. (1998) did not find any effect of the electrolytic balance (100, 150, 200, 250 e 300 mEq) on the humidity of the excreta up to 7-days of age. Borges et al. (1999) show ed t hat diet s containing 0.30 and 0.45% Na caused litter humidity similar to those obtained w ith the use of commercial diets at this age. Although not quantified, diets w ith an electrolytic balance betw een 246 and 277 mEq, w ith Na levels low er than 0.45% , apparently did not affect litter humidity up to 7 days of age of the chicks.
In conclusion t he dat a of t his st udy suggest t hat , t he elect rolyt ic balance of t he f eed (Na+K-Cl) int erf ere in t h e p er f o r m an ce o f t h e ch ick s, an d t h e id eal elect ro lyt ic b alan ce, o b t ain ed b y Na an d Cl levels manipulat ion, w as 246 and 277 mEq/kg f or f eed:gain rat io and w eight gain, respect ively. W hen f ormulat ing pre-st art er diet s w hich t ake int o account t he concept of elect rolyt ic balance, ext rem e levels of Cl (0.77% ) and K (1.05% ) must be avoided.
Table 1 – Electrolyte composition of the experimental diets (% ).
M ongin Number Experiments
(mEq/kg) I II
Na K Cl Na K Cl
40 0.15 0.75 0.77 0.15 0.75 0.77
140 0.25 0.75 0.57 0.20 0.85 0.58
240 0.35 0.75 0.37 0.25 0.95 0.40
Table 2 – Performance of chicks receiving different (Na+K-Cl) electrolytic balance in the diet up to 7 days of age (Experiment I and II).
mEq/kg Weight gain (g) Feed intake (g) Feed:gain
Experiment I
40 117c2 175 1.508a
140 124bc 178 1.445ab
240 138a 185 1.350b
340 131ab 186 1.418ab
CV 1 (% ) 5.14 4.93 4.89
Experiment II
40 120 151 1.262
140 125 155 1.244
240 128 161 1.255
340 125 151 1.213
CV 1 (% ) 5.34 4.60 3.33
1 - Coefficient of variation.
2 - M eans w ith different letters in the columns are different (p<0,05).
Figure 1 – Effects of the Na+K-Cl electrolytic balance of feed on w eight gain and
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