Abstract: A soy protein based semi-purified diet was used to estimate the optimum electrolyte balance (meq Na+, K+, Cl-/kg diet) at 3 levels of dietary crude protein. Results indicated that in diets containing 14.3% Crude Protein (CP), the optimum electrolyte balance was approximately 250 meq/kg; at 21.4% CP the optimum was about 325 meq/kg and at 28.6% CP it was about 400 meq/kg. A conventional 21% CP corn-soy broiler diet which, by calculation, contained 228 meq Na+, K+, Cl-/kg was used in two subsequent experiments. In both experiments, it was found that feed intake, gain and feed efficiency were significantly improved (p<0.05) by the addition of 100 meq Na+, K+/kg diet in diets containing 56.4 meq Cl/kg, thus, confirming an optimum electrolyte balance of about 325 meq/kg in diets containing 21% CP. It was concluded that the optimum dietary electrolyte balance of broiler chicks is dependent on diet crude protein content. Further, within the range of 14-28% CP, the optimum electrolyte balance is increased by about 11 meq/kg per 1 percentage unit increase in diet crude protein content.
INTRODUCTION
Acid-base balance in birds is influenced by some factors which include the environmental condition, diet and metabolism. All these factors alter the regulation of pH in the blood and tissues (Olanrewaju et al., 2007).
Experiments have shown that addition of salt in the diet or water can affect the acid-base balance of animal (Borges et al., 2004). Derjant-Li et al. (2002) have also reported the essential role that dietary electrolytes exert on the acid base balance. Adekunmisi and Robbins (1985, 1987a and b) in their series of experiments showed that there is a marked interaction between dietary crude protein level and dietary electrolyte balance (Meq Na+, K+, Cl-/kg diet). Namely, increasing the electrolyte balance from 200-350 meq/kg or more, improved gain and feed consumption of birds fed high protein diets, but depressed growth of birds fed low protein diets. It was found that although, dietary electrolyte balance did affect kidney asparaginase activity, plasma uric acid concentration and metabolic acid-base status, these observed effects were not statistically correlated with the growth response. The nature and the magnitude of the electrolyte balance x protein interaction observed in these experiments were apparently the result of a specific effect on feed consumption.
Interest has been centered on these monovalent electrolytes (Na, K, Cl) largely because of their prominent effect on metabolic acid-base balance and because they are among the minerals most likely to be varied in diet formulation (Mongin and Sauveur, 1977; Leach, 1979). Mongin and Sauveur (1977) indicated that an electrolyte balance of 250 meq (Na+, K+, Cl-/kg diet) was optimum for growth of young chicks. Johnson and Karunajeewa (1985) observed that the optimum electrolyte balance lies between 250 and 300 meq/kg diet. However, in neither of these reports was the effect of protein level evaluated. The electrolyte balance x crude protein interaction observed in preceding studies (Adekunmisi and Robbins 1985, 1987a and b) strongly suggested that the electrolyte balance required to maximize growth is proportional to the level of dietary protein.
The present study was undertaken to quantify the optimum dietary electrolyte balance at three protein levels utilizing semi-purified diets and to evaluate the applicability of such estimates to a conventional corn-soy diet.
MATERIALS AND METHODS
In each experiment, female Peterson crossbred broiler chicks were used. Chicks were randomly distributed to four replicate groups of 6 chicks each per treatment in Experiment 1 and to three replicate groups of 6 chicks each per treatment in experiments 2 and 3. The chicks were housed in electrically-heated battery brooders in an environmentally-controlled room which was kept at 25oC. Chicks were fed the experimental diets from day 4-32 posthatching in Experiment 1; from day 5-26 posthatching in Experiment 2 and from day 1-29 posthatching in Experiment 3. A corn-soy broiler starter diet was fed to the chicks for the day preceding the initiation of the experiments.
| Table 1: | Percentage Composition of the Basal Diets (Experiment 1)a |
aContained by calculation 3200 kcal ME/kg. bAs analysed. cProvided per kg diet: calcium chloride dihydrate, 4.14 g; calcium carbonate, 2.47 g; dibasic calcium phosphate, 25.2 g; monobasic calcium phosphate, 8.14 g; magnesium oxide, .568 g; manganous sulfate monoghydrate, cupric sulfate pentahydrate, 20 mg; boric acid, 9 mg; sodium molybdate, 9 mg, ethylene diaminedihydroiodide, 40 mg, cobalt sulfate septahydrate, 1 mg; sodium selenite, 0.21 mg; silica, 4.65 g. dBaker et al. (1979) | |
| Table 2: | Elemental Composition of the Experimental Diets (Experiment 1)a |
| aCalculations based on mineral analyses of all
raw ingredients of the diet. bCalculated as meq (Na+, K+, Cl-)/kg diet at the expense of cellulose |
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| Table 3: | Composition of the basal diet (Experiments 2 and 3) |
aProvided per kg diet: vitamin D3, 750 ICU; vitamin A, 4,175 IU; riboflavin, 4.74 mg; vitamin B12, .011 mg; Choline, 468 mg; niacin, 41.7 mg; D-Ca-pantothenate, 7.34 mg | |
Feed and water were provided ad libitum throughout the experimental periods.
The composition of the semi-purified basal diets and the elemental composition of all experimental diets utilized in Experiment 1 are presented in Table 1 and 2, respectively. All diets were formulated to meet or exceed the nutrient requirements for growing chicks (NRC, 1994). The experimental treatments consisted of 3 levels of dietary electrolyte balance (meq Na+, K+, Cl-/kg diet) at each of the three protein levels. The choice of the various electrolyte balances used was based on preceding experiments (Adekunmisi and Robbins, 1987a and b) and governed by the Na and K content of the basal diets. The concentrations of these elements increase as the protein level increases. These electrolyte balances were achieved by the addition of Na and K-citrate.
The Na and K concentrations of all dietary ingredients were determined by atomic absorption spectrophotometry and Cl was measured using a Dionex ion chromatograph.
Experiments 2 and 3 were conducted to evaluate the applicability of the determined optimum electrolyte balance (325 meq/kg at 21.4% crude protein) estimated in Experiment 1 to a conventional corn-soy based diet containing 21% crude protein. The experimental diets were formulated based on ingredient compositions of NRC (1994). The electrolyte balance of the basal (control) diet was calculated to be 228 meq/kg (Table 3). The experimental diet was prepared by the addition of 100 meq Na+, K+ (1:2.27 molar ratio) to the basal diet at the expense of corn, thus, achieving an electrolyte balance of 328 meq/kg.
RESULTS AND DISCUSSION
The results of Experiment 1 are presented in Table 4. The quadratic effect of electrolyte balance on gain was significant (p<0.05) at each level of crude protein. There were no significant effect of electrolyte balance on feed intake of chicks fed diets containing either 21.4% or 28.6% dietary crude protein, however, there was a significant (p<0.006) quadratic effect in chicks fed diets containing 14.3% crude protein. The quadratic effect of electrolyte balance on feed efficiency was significant (p<0.005) when diets containing either 14.3 or 21.4% crude protein were fed. The linear effect of electrolyte balance on feed efficiency was significant (p<0.005) for chicks fed 28.6% CP diets.
Within each level of crude protein, feed efficiency and gain were highest when diets contained the middle level of electrolyte balance, thus, indicating optimum electrolyte balances of near 250 meq/kg in diets containing 14.3% CP, near 325 meq/kg in diets containing 21.4% CP and near 400 meq/kg in diets containing 28.6% CP.
| Table 4: | Effect of dietary electrolyte balance on performance of chicks at different protein levels (Experiment 1)a |
aData are means of quadruplicate groups of 6 female chicks each. Chicks were fed the experimental diets from day 4 to day 32 posthatching. Average initial weight was 71 g. bSee Table 2 for complete description. CQuadratic effect of electrolyte balance was significant (p<0.005) at both 14.3 and 21.4% CP levels and was significant (p<0.05) at 28.6% CP. dQuadratic effect of electrolyte balance was significant (p<0.005) at 14.3%. eQuadratic effect of electrolyte balance was significant (p<0.005) at both 14.30 and 21.4% CP levels. Linear effect of electrolyte balance was significant (p<0.005) at 28.6% CP diets. fPooled standard error of the mean | |
| Table 5: | Effect of electrolyte balance on growth of chicks fed a practical-type diet (Experiment 2 and 3) |
aData are means of 3 groups of 6 chicks each fed the diets from 5-26 day posthatching. Average initial weight was 59 g. The effect of electrolyte balance was significant (p<0.04) for each variable. bData are means of 6 groups of 6 chicks each fed the diets from 1-29 day posthatching. Average initial weight was 40 g. The effect of electrolyte balance was significant (p<0.01) for each variable. cPooled standard error of the mean | |
The optimal electrolyte balance of 325 meq/kg for diets containing 21% CP is close to the range (250-300 meq/kg) reported by Johnson and Karunajeewa (1985). Mongin and Sauveur (1977) reported an optimum electrolyte balance of 250 meq/kg, but it is not clear what levels of dietary crude protein were used in their experiments. The results of Experiments 2 and 3 were presented in Table 5. Addition of Na and K - citrate to the conventional corn-soy diet to achieve an electrolyte balance of 328 meq/kg resulted in a significant (p<0.05) increase in feed intake, body weight gain and feed efficiency in both Experiments 1 and 2.
The present studies demonstrated that an electrolyte balance of about 325 meq/kg is required to support maximum gain and feed efficiency of broilers fed typical corn-soy-based commercial broiler diets containing 21% CP. Moreover, the data indicated that within the range of 14-28% dietary crude protein, the optimum electrolyte balance is increased by approximately 11 meq (Na+, K+, Cl-/kg) per 1 percentage unit increase in diet protein content.