By D. M. Hooge, K. R. Cummings, and J. L. McNaughton
The use of coccidiostats, especially ionophores, in broiler chicken feeds is the primary method for prevention and control of the economically important disease coccidiosis. Sodium sources, such as sodium chloride (NaCl; W.W. Saylor and J.C. Fleet, circa 1984, unpublished data, personal communication) and sodium bicarbonate (SBC; Hooge et al., 1999), appear to complement ionophores, but their relative efficacies have not been established. Sodium sulphate decahydrate (SSD), primarily studied for its methionine-sparing ability at marginal or deficient levels of dietary methionine (Soares, 1974), has soluble sodium which can potentially interact with ionophores. Sulphate per se acidifies body fluids, as shown, for example, by Saroka and Combs (1986) using each of two sources of dietary methionine, a sulphur-containing amino acid, to lower urinary pH in broiler chickens.
The influence of sodium sources when using various Coccidiostats needs to be compared in corn-soy-meat based versus corn-soy based diets because the latter have lower potassium, another monovalent cation, due to some of the soybean meal being replaced by animal by-products. Pesti (1998) observed no significant differences in male broiler performance on litter with semduramicin (Aviax®)1 at 25 mg/kg in corn-soy or corn-soy-meat (12% animal byproduct) diets, and combined-sex broilers fed semduramycin in battery brooders showed no significant performance differences among three electrolyte balances (Na+K-Cl =231, 275, or 362 mEq/kg), adjusted with a variety of electrolyte salts, including SBC plus potassium carbonate.
Hurst et al. (1974) found that broiler chicks in battery brooders performed better with 0.30% dietary salt (NaCl) than with 0.075 to 0.225% NaCl, and performed equally well with 0.30% compared to 0.375% NaCl, when monensin was included at 121.3 mg/kg in the feed to four weeks of age. Nam et al. (1979) conducted litter and battery brooder trials with broiler chicks fed corn-soy diets and found 0.15% sodium (source not mentioned) adequate with either monensin or lasalocid compared to 0.10, 0.20, or 0.35% sodium. Higher sodium levels did not give any additional benefit. Gard et al. (1980) conducted a series of seven litter pen trials involving 218,200 birds (210 pens) with monensin at 100 or 121 ppm and sodium at 0.11, 0.17 to 0.19, and 0.24 to 0.27% using NaCl as the supplement. Broilers receiving 0.17 to 0.19% sodium had heavier (P < 0.10) weights than those fed 0.11% or 0.24 to 0.27% sodium. Increasing monensin from 100 to121 mg/kg did not appear to increase the requirement for sodium from NaCl. Edwards (1985) found significant improvements in 3-wk body weights and feed efficiencies of broiler chicks with or without monensin with increasing dietary NaCl levels from 0.1125 to 0.225, 0.3375, and 0.45%.
Mongin (1968) stated that "sodium bicarbonate seems to be a privileged element" because it provides sodium, favourably affects blood pH ("can influence the balance of H+ ions"), and supplies beneficial bicarbonate. Damron et al. (1986) concluded that the sodium in SBC was equally bioavailable to that in NaCl for broiler chicks. Jensen (1982) reported that 4-wk broiler chick weights were significantly improved by 0.65% dietary SBC, compared to results of the control or 0.45% extra NaCl treatment, when a high level of monensin (160 mg/kg) was fed. With monensin at an approved level of 120 mg/kg or at 0 mg/kg, no significant sodium source effects were found.
Acidity control by SBC
Coccidial infected chicks were found by Stephens et al. (1974) an increase in acidity (decrease in pH) of intestinal contents near the invasion sites (infected vs control intestinal pH): E. acervulina 4.96 vs 6.02; E. brunetti 5.84 vs 7.02; and E. mivati 5.58 vs 6.40 (Stephens et al., 1974). This was presumed to be due to loss of cellular contents, which are acidic, into the lumen of the intestine or to destruction of cells that produce the hormone secretin which regulates bicarbonate output from the pancreas. With E. necatrix, significant reductions in pH of intestinal contents have been observed on the sixth and ninth days post-inoculation of a severe infection (Stephens, 1965). Fox et al. (1987) reported that feeding broiler chicks a 1% level of SBC numerically improved gains and feed efficiencies when birds were uninfected or inoculated with E. acervulina compared to results of unsupplemented chicks. However, 1% dietary SBC failed to alleviate the duodenal pH decrease (pH 4.35 vs 6.51 in control duodenal contents) in infected chicks.
Merrill (1993) found from a survey of SBC use in broiler feeds in Western Europe that 0.2% was the most common level, in conjunction with 0.1% added NaCl, and the main purpose was to lower dietary chloride and reduce wet litter problems. Diets typically contained not more than 25% soybean meal and included fishmeal, the latter having about 0.60% each of sodium and chloride. In diets without fishmeal, it was typical to add up to 0.4% SBC. Augustine (personal communication) discovered that SBC in the absence of a coccidiostat substantially increased the number of sporozoites in cross-sectional intestine (E. acervulina, +48%; E. maxima, +68%) following inoculation compared to inoculated control birds. With SBC plus 121 mg/kg monensin, intestinal E. acervulina sporozoite counts were increased by 6.4% and E. maxima developmental stage counts were increased by 104%, compared to results for monensin alone. Enhancement of coccidial invasion by SBC was associated with reduced coccidial lesions and improved performance of chicks, suggesting a possible stimulation or acceleration of immunity, appearing to improve the efficacy of the ionophore coccidiostat. This effect was opposite that of betaine, also studied by Augustine (1997), which helps cells to resist the invasion of coccidian into intestinal epithelium and enhance ionophore effectiveness. Hooge et al. (1999) reported optimal levels of dietary SBC to be 0.20 to 0.30% for broilers fed ionophores, grown on built-up litter, and given a coccidial inoculation, based on significant improvements in weights, feed efficiencies, coccidial lesion scores, mortalities, and carcass yields compared to control results in several dose-response studies. All parameters did not show significant differences in every test, but each parameter was significantly improved in one or more trials.
Sodium and anticoccidials work together
The objectives of the four experiments reported in this article were to evaluate dietary SBC (0 or 0.20%) with each of three ionophore coccidiostats or a chemical coccidiostat and to compare corn-soy versus corn-soy-meat diets supplemented with sodium chloride, bicarbonate, or sulphate for broiler chickens grown on built-up litter or in battery brooders. The influence of SBC on diet type was evaluated because corn-soy-meat diets contain lower potassium and higher chloride than corn-soy diets.
Effects on production parameters
When control diets were compared with sodium bicarbonate (SBC) at 0.2% in broiler diets, a diet containing SBC and monensin at 110 g/ton significantly reduced coccidial lesion scores by 79.7%, produced body weights heavier by 0.98%, and improved mortalityadjusted feed efficiency by 1.22% compared to control results (Table 1). Mortality was low during the 45-d trial.
When broilers were grown on built-up litter and given a coccidial challenge without a coccidiostat, addition of 0.20% dietary SBC had essentially no effect on body weight, uniformity, feed efficiency, mortality, or breast meat yield compared to control results (Table 2). Monensin plus 0.20% SBC significantly improved body weight, coefficient of variation, and feed efficiency compared to results for the respective control diet without SBC. Mortality was significantly (P < 0.05) reduced by each of the coccidiostats in combination with 0.20% SBC compared to respective 0% SBC control results. Breast meat yield as a % of live weight was significantly (P < 0.05) increased by 0.20% SBC and either lasalocid, monensin, or salinomycin compared to control diets without SBC.
In 2 experiments, identical 2 x 4 factorial designs with two diet types (corn-soy or corn-soy-meat) and four sources of sodium were utilised. Sodium sources were: SBC, sodium chloride (NaCl), or sodium sulphate decahydrate (Na2SO4-10H2O). A third experiment was conducted for 45 d on litter, and a further experiment was carried out on raised wire for 21 d. Table 4 contains results for birds inoculated with three species of coccidia at 14 d of age, grown on built-up litter, and fed corn-soy versus corn-soy-meat diets with various sodium sources. Using corn-soy diets with monensin at 121 mg/kg, none of the sodium sources significantly (P < 0.05) increased body weight, but 0.20% SBC or 0.139% sodium chloride (NaCl) significantly (P < 0.05) improved weight uniformity compared to controls, with sodium sulphate decahydrate (SSD) producing an intermediate and significant (P < 0.05) result.
Adding either 0.20% SBC or 0.139% NaCl significantly (P < 0.05) improved mortality adjusted feed efficiency and mortality compared to those of control or 0.397% SSD diets. Using corn-soy-meat diets, body weights were not significantly affected by sodium sources, but SBC or NaCl significantly (P < 0.05) reduced body weight coefficients of variation (CV) % compared to the control, with SSD treatment CV % being intermediate and significantly (P < 0.05) different from control (Table 3). Mortality adjusted feed efficiency and mortality were significantly better with either 0.20% SBC or 0.139% NaCl than with control or SSD treatments.
Sodium and water balance
In Table 3, for corn-soy diets, litter moisture was significantly (P < 0.05) increased with 0.20% SBC, but to a lesser extent than with 0.139% NaCl, compared to control or SSD results. The SSD was added "on top" of the formula in place of corn, as were the other sodium sources, contributing extra sodium, but did not stimulate water intake to the same extent as SBC or NaCl. Excess water intake and excretion resulted in increased moisture in the litter. The chloride ion appeared to be responsible for some of the additional litter moisture content because NaCl increased litter moisture to a greater extent than either SBC or SSD which contain no chloride. Breast meat yield was significantly increased by either SBC or NaCl compared to control or SSD treatments.
In a fourth experiment, there were four replicate battery brooder pens of 10 chicks each (5 males, 5 females) per treatment. This battery brooder trial was identical in design to the litter-pen experiment, except that it was conducted for only 21 d, and water intake and excretion were also determined (Table 4). With corn-soy diets containing monensin at 121 mg/kg, extra supplemental NaCl significantly (P < 0.05) improved 21 d body weight compared to other treatments. Mortality was significantly (P < 0.05) better with diets containing SBC or extra NaCl than with control or SSD diets. Using corn-soymeat diets, 21-d body weight, feed efficiency, and mortality were significantly (P < 0.05) improved with SBC or NaCl compared to the control diet, and SSD results were not significantly different from the control values.
Corn-soy diets with either of the three sodium sources gave significantly (P < 0.05) lower 21-d coccidial lesion scores than unsupplemented diets. The 14- to 21-d water intake was significantly increased by 0.139% extra NaCl compared to all other treatments. Water excretion as a % of intake was significantly increased by extra NaCl compared to the control, and dietary SBC gave an intermediate and significant increase as well. The SSD was without effect on water intake. Using corn-soy-meat diets, coccidial lesion scores were significantly improved by diets containing each of the sodium sources compared to the control diets. Water intake was significantly (P < 0.05) elevated only with extra NaCl compared to the control and SSD treatments. The 0.139% extra NaCl diets significantly (P < 0.05) increased 14- to 21- d water excretion compared to all other treatments.
Sodium enhances coccidiostat efficacy
Using broiler chickens on built-up litter and inoculated with coccidian by water, dietary SBC (0.20%) significantly (P<0.05) enhanced the effects of coccidiostats on body weight, weight uniformity, feed efficiency, coccidial lesion scores (all with monensin), mortality (halifuginone, lascalocid, monensin, salinomycin), and breast meat yield (lasalocid, monensin, salinomycin). The improvement in breast meat yield may have been due to an increase in tissue or in tissue water content due to added dietary sodium. Excess NaCl is known to cause tissue swelling due to an increase in intercellular water rather than intracellular water, and a similar situation may have occurred with SBC. At this point, the mode of action of breast yield improvement by dietary SBC has not been determined.
The SBC (0.20%) added "on top" of the formula, in place of an equal amount of corn, raised dietary sodium 0.054%, moderately increasing water intake, water excretion, and litter moisture. Therefore, SBC should probably be "formulated in", but the resulting lower levels of total sodium and chloride, due to partial replacement of NaCl, may then influence results and would need to be verified in future research.
In the extra NaCl treatments, total added NaCl levels in the starter, grower, and finisher diets respectively were: corn-soy 0.429, 0.409, and 0.389%; and corn-soy-meat 0.419, 0.369, and 0.319%. In both the corn-soy and corn-soy-meat extra NaCl treatments, total calculated sodium levels in the starter, grower, and finisher diets, respectively, were 0.274, 0.254, and 0.234%. In the extra NaCl treatments, chloride levels in starter, grower and finisher diets respectively were corn-soy 0.294, 0.284, and 0.274%; corn-soy-meat 0.374, 0.354 and 0.324%.
Adding extra NaCl (0.139%) "on top" of complete feed formulas, in place of corn, significantly (P < 0.05) enhanced the effectiveness of monensin on weight uniformity, feed efficiency, coccidial lesion score, mortality, and breast meat yield. However, the extra NaCl had strong and significant (P < 0.05) effects on water intake (+36.9%), water excretion (+27.2%), and litter moisture (+22.1%). Percentages in parentheses were averaged across diet types.
Effects of dietary sodium sources (bicarbonate, chloride, and sulphate) with monensin on broiler production and processing parameters were similar in corn-soy and corn-soy-meat diets. The SSD produced some significant (P < 0.05) effects, but these changes were typically smaller and weaker than those with SBC or NaCl when contributing equal amounts of sodium (i.e., 0.054%).
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