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Effects of dietary electrolyte balance on the chemistry of blood and urine in lactating sows and sow litter performance^1,2

Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201

	Abstract

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One hundred fifty-three sows (average parity of 2.2) were used to determine the effects of dietary electrolyte balance (calculated as mEq/kg of diet for Na + K - Cl) on sows and their litters during lactation. The sows were fed corn-soybean meal-based diets (1.0% lysine, 1.0% valine, 0.95% Ca, and 0.80% P; as-fed basis) starting on d 109 of gestation and throughout the 21-d lactation experiment. Dietary electrolyte balance (dEB) was 0, 100, 200, 350, and 500 mEq/kg (as-fed basis), well above and below the dEB of 185 mEq/kg found in a simple corn-soybean meal-based lactation diet. To achieve the desired dEB, diets had the following: 1) 1.8% HCl (6 N) and 1.06% CaCl₂, 2) 1.0% CaCl₂, 3) 0.04% NaHCO₃, 4) 1.29% NaHCO₃, and 5) 2.54% NaHCO₃ (as-fed basis). Increasing dEB increased blood pH (linear and quadratic effects, P < 0.001), partial pressure of carbon dioxide (linear effect, P < 0.001), HCO₃^- concentration (linear and quadratic effects, P < 0.001), and blood base excess (linear and quadratic effects, P < 0.001). However, increased dEB resulted in lower blood concentrations of K (linear and quadratic effects, P < 0.04), Cl (linear and quadratic effects, P < 0.001), and ionized Ca (linear and quadratic effects, P < 0.001). Changing dEB did not affect ADFI; water usage, litter weight gain; sow weight change; sow backfat change; percentages of CP, lactose, and fat in the milk; percentage of sows returning to estrus; days to estrus; and number of pigs born alive in the subsequent litter (P = 0.06). However, piglet survivability to d 10 and overall was greatest with the lower dEB treatments (linear effect, P < 0.05). The pH (linear and quadratic effects, P < 0.001) and colony forming units of total bacteria (linear effect, P < 0.03) in the urine increased as dEB of the diet was increased. In conclusion, dEB had pronounced effects on the physiological status of sows and decreasing dEB below that in a simple corn-soybean meal-based diet decreased bacterial counts in the urine and increased piglet survivability. However, milk composition, sow and litter weights at weaning, and subsequent rebreeding performance of the sows were not affected by dEB.

Key Words: Acid-Base Equilibrium • Electrolytes • Lactation • Pigs • Sows

	Introduction

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Maximizing the performance of sows and litters during lactation is a major objective of nutritionists. Feed-processing technologies (Wondra et al., 1995b,c; Johnston et al., 1999), amino acid supplementation (Knabe et al., 1996; Richert et al., 1996), and increased dietary energy density (Boyd et al., 1982; Noblet and Etienne, 1986) have been used to address this objective. Research in dairy cattle (Goff and Horst, 1998) and laying hens (Makled and Charles, 1987; Balnave and Muheereza, 1997) indicated positive effects on metabolism (e.g., reduced incidence of milk fever and greater eggshell quality) when the dietary electrolyte balance (dEB) was modified. In finishing pigs, Patience et al. (1987) reported increased ADFI when dEB was increased from 68 to 346 mEq/kg, but Wondra et al. (1995a) reported no change in ADFI as dEB was increased from 177 to 399 mEq/kg. Furthermore, Johnson and Karunajeewa (1985) reported decreased ADFI in broilers fed diets with dEB less than 180 mEq/kg, and Patience et al. (1987) reported decreased ADFI in growing pigs fed a diet with dEB of -85 mEq/kg. However, the impact of altering dietary electrolyte balance (dEB) on lactation and/or reproductive performance in sows has not been thoroughly explored. Thus, the objective of the experiment reported herein was to determine the effects of dEB on chemistry of blood and urine in lactating sows and on sow and litter performance.

	Materials and Methods

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Pilot Study for Treatment Selection.

We were not concerned about depressed ADFI in sows as dEB was increased above that in a simple corn-soybean meal-based diet (i.e., approximately 185 mEq/kg), but the effect of decreased dEB on ADFI was a concern for the lactation experiment. To determine the minimum dEB that could be used in a lactation experiment without depressing ADFI, we initially conducted a 21-d pilot study. A small group of sows (30 sows, Line C 22, parities 1 to 4; PIC, Franklin, KY) was used. On d 109 of gestation, the sows were moved into a farrowing facility and given lactation treatments that were equalized across parity. The diets (Table 1) were corn-soybean meal-based and formulated to meet or exceed all nutrient concentrations recommended by the National Research Council (NRC, 1998). The dEB treatments of -200, -100, 0, 100, and 200 mEq/kg were selected to bracket the dEB suggested as problematic in finishing pigs by Patience et al. (1987). To achieve the desired dEB while keeping the Ca:P ratios in the diets constant, the -200 treatment had 1.98% CaCl₂, 1.54% HCl (6 N), and 1.85% H₃PO₄; the -100 treatment had 1.98% CaCl₂, 1.05% HCl (6 N), and 1.85% H₃PO₄; the 0 treatment had 1.98% CaCl₂ and 1.84% H₃PO₄; the 100 treatment had 1.0% CaCl₂; and the 200 treatment had 0.04% NaHCO₃. The sows (six per treatment) were allowed ad libitum access to feed (four feedings per day) and water (nipple waterer with a flow rate of 1.3 L/min). Litter size was standardized within 24 h postfarrowing, and all sows had at least 10 pigs after cross-fostering. Feed was weighed back on d 7 and at weaning to allow calculation of ADFI.

One hundred fifty-three sows (Line C 22; PIC, Franklin, KY) were used in the 21-d lactation experiment. On d 109 of gestation, the sows (parities 1 to 4) were moved into a farrowing facility and assigned lactation treatments in a manner that equalized parity across the dietary treatments. The diets were corn-soybean meal-based (Table 2) with dEB of 0, 100, 200, 350, and 500. The diets were formulated to meet or exceed all nutrient concentrations recommended by the National Research Council (NRC, 1998). In addition, all diets were formulated to constant Ca, P, and K concentrations, with Cl and Na varied to achieve the desired dEB. The lowest dEB (0) was achieved by mixing CaCl₂ (1.06% of the total diet) and 6 N HCl (1.80% of total diet) into the corn portion of the diet before the other ingredients were added. The treatment with a dEB of 100 had 1.0% CaCl₂ with no HCl, and the diets with dEB of 200, 350, and 500 had 0.04, 1.29, and 2.54% NaHCO₃, respectively.

The sows were allowed ad libitum access to feed (four feedings per day) and water (nipple waterer with a flow rate of 1.3 L/min). Each farrowing crate had a water meter (Neptune/Schlumberger Type TM, Greenwood, SC), so water disappearance could be determined. In addition, feed was weighed back on d 10 and at weaning to allow calculation of ADFI. The sows were weighed and scanned ultrasonically (PREG-ALERT Type 2E, Renco Corp., Minneapolis, MN) at the first rib, last rib, and last lumbar vertebra and averaged at farrowing, d 10, and weaning. Litter size was standardized within 24 h postfarrowing, and all sows started with at least 10 pigs after cross-fostering. Piglet weights were recorded after cross-fostering, d 10, and weaning.

Between d 10 and 12 of lactation, approximately 75 mL of urine (midstream) was collected at 0600 from each sow. The samples were analyzed immediately for pH (PHEP3F, Hanna Instruments, Woonsocket, RI) and total bacteria (Carter and Cole, 1990). Subsamples were frozen for later analyses of creatinine (Sigma kit 555-A, Sigma Chemical Co., St. Louis, MO). In addition, approximately 2 h after the morning feeding (i.e., at 0800) on d 10 to 12 the sows were restrained with a nose snare and injected with 0.5 mL of oxytocin (via ear vein) to enhance milk letdown. A total sample of about 100 mL of milk was collected from the first three productive mammary glands on each side. Lactose, fat, and protein in the milk were determined with a Bentley ChemSpec Analyzer 2000 (Chaska, MN), and pH of the milk was recorded. Finally, venous blood was collected from the brachial region of each sow’s neck, immediately placed on ice, and, within 20 min of collection, analyzed (NOVA Stat Profile IV, NOVA Biomedical, Waltham, MA) for pH, pCO₂, pO₂, Na, K, Cl, and Ca. Bicarbonate, total CO₂, base excess of the blood and extracellular fluid, normalized Ca, and electrolyte balance were calculated (NCCLS, 1982). Temperature of the blood at the time of analyses was used to adjust the lab values to those anticipated if the blood had still been in a sow having a standard body temperature of 39°C (Pond and Houpt, 1978). Plasma urea N was determined using the procedures of Marsh et al. (1965) and an autoanalyzer (Alpken Corp., Clackamas, OR). Finally, concentrations of DM, ash, CP, ether extract, Ca, P, Na, K, and Cl (AOAC, 1990) and pH were determined for the diets.

At weaning, the sows were moved to an environmentally controlled gestation barn and bred during their first estrus. Days to rebreeding was calculated as the days from weaning to first service and sows not rebred within 30 d were sold. The sows were housed in gestation stalls (0.53 m x 1.78 m) during rebreeding. On d 30 of gestation, the sows were moved from their gestation stalls to dirt lots with sheds.

During rebreeding and gestation, the sows were fed the same sorghum-soybean meal-based diet formulated to meet or exceed all National Research Council (NRC, 1998) standards for nutrient concentrations. During summer months, the sows were fed 1.8 kg/d of the diet and during winter months the gestation ration was increased to 2.3 kg/d. On d 109 of gestation, the sows were moved back into the farrowing facility to allow determination of number of pigs born live.

All data were analyzed using the GLM procedure of SAS (SAS, 1996) with sow as the experimental unit. Polynomial regression (Peterson, 1985) was used to evaluate the shape of the response to increasing dEB. Lactation length, parity, and initial litter size (after cross-fostering) were used as covariates for analyses of sow BW change, backfat change, ADFI, water usage, pigs weaned per litter, litter weaning weight, litter weight gain, survivability of the piglets, percentage of the sows that returned to estrus, and days to estrus. Parity was used as a covariate for analyses of milk composition and parity and lactation length were used as covariates for number pigs born alive in the subsequent litter.

	Results and Discussion

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Pilot Study for Treatment Selection.

At d 7 of the pilot study, ADFI was similar among sows fed the three highest dEB treatments of 0, 100, and 200 mEq/kg (4.6, 4.8, and 4.8 kg/d, respectively). However, sows fed the lowest dEB treatments (-200 and -100 mEq/kg) had ADFI of only 2.4 kg/d. With the low ADFI (linear effect, P < 0.03) in the sows and the poor appearance of the sows and their litters, the dEB treatments of -200 and -100 mEq/kg were deleted from the experiment. The other sows were continued on their treatment diets until weaning (d 21).

For the dEB treatments of 0, 100, and 200 mEq/kg, the overall ADFI values of 5.1, 5.4, and 5.3 kg/d were not different (P = 0.45). Thus, we concluded that the lowest dEB to use for the larger-scale lactation experiment should be 0 mEq/kg.

Lactation Experiment.

Blood pH of less than 7.0 (i.e., >100 nmol/L of H⁺) or greater than 7.7 (i.e., <20 nmol/L of H⁺) can cause death (Seldin and Giebisch, 1989) and, thus, pH of the blood is closely regulated. In our experiment, blood pH was increased from 7.33 to 7.43 (linear and quadratic effects, P < 0.001) as dEB was increased from 0 to 500 mEq/kg (Table 3). Thus, alterations in dEB did influence blood H⁺ concentrations in lactating sows, but we observed no affects on sow appearance or temperament that might indicate better or worse metabolic status. In addition to our research, Patience and Chaplin (1997) reported that changes in dEB great enough to elicit measurable changes in blood pH of finishing pigs did not decrease growth performance or apparent well-being of the animals.

The concentration of tCO₂, which reflects the changes in pCO₂ plus HCO₃^-, increased (linear and quadratic effects, P < 0.001) as dEB was increased. In addition, base excess in the blood (linear and quadratic effects, P < 0.001) and extracellular fluid (linear quadratic effects, P < 0.002) increased as dEB was increased. Hamilton and Thompson (1980) reported similar results as dEB was increased from -330 to 265 mEq/kg in laying hens; that is, less HCO₃^- was converted to CO₂ as the birds were changed to a less-acidotic diet. Also, Patience and Chaplin (1997) reported that, in pigs, base excess of the blood changed from -0.3 mmol/L to 5.8 mmol/L as dEB was changed from -20 to 163 mEq/kg. The authors argued that the increased base excess was associated with decreased dietary acid load.

The pO₂ (partial pressure of oxygen in the gas phase) in equilibrium with the blood was unaffected (P = 0.12) by acid-base status of the sow (Table 3). Randall (1971) indicated that insufficient O₂ in the blood of piglets at parturition was a major cause of low viability, and thus, dietary treatments that increased saturation of the sow and fetal blood with O₂ could increase piglet survivability. However, in our experiment pO₂ in the sows was not affected by changing dEB from 0 to 500 mEq/kg.

As for blood electrolytes, concentrations of Na were not affected consistently, but concentrations of K (linear and quadratic effects, P < 0.04) and Cl (linear and quadratic effects, P < 0.001) decreased with increased dEB (Table 3). Simmons and Avedon (1959) also reported a negative relationship among blood pH and K concentrations, a relationship that reflects the movement of K⁺ and H⁺ into and out of cells in response to changes in blood pH. Futhermore, Yen et al. (1981) reported that blood Cl increased and decreased in concert with changes in dietary Cl concentration that resulted from adding or removing CaCl₂ in the diet. Furthermore, electroneutrality in the extracellular fluid must be maintained constant within the body; thus, the decrease in a cation, in this case K, must happen to compensate for the decrease in blood Cl levels. This helps to further explain the decreased concentrations of K and Cl in the blood as dEB was increased.

Concentrations of both ionized (linear and quadratic effects, P < 0.001) and normalized (linear effect, P < 0.005) Ca in the blood decreased as dEB was increased (Table 3). This can be explained (Seldin and Giebisch, 1989) as the result of less bone mobilization being needed to buffer the extracellular fluid with the decrease in H⁺ concentration in the blood as dEB was increased. Tilley (1997) also reported decreased blood Ca concentrations with increased dEB. Goff and Horst (1998) reported a 53% reduction in the incidence of milk fever among dairy cows fed diets with a low dEB. They suggested that anionic salts (e.g., CaCl₂ or NH₄Cl) prevented milk fever by acidifying the blood and restoring responsiveness of bone tissue to parathyroid hormone.

Concentrations of urea N in the plasma (P = 0.25) and creatinine in the urine (P = 0.33) did not differ among sows fed the dietary treatments (Table 3). High concentrations of urea N in the plasma and creatinine in the urine are considered indicators of excess catabolism of lean body mass. Thus, the lack of differences in plasma urea N and urinary excretion of creatinine in our experiment suggest no major differences in catabolic state among sows fed the various dEB treatments.

The pH of the urine was increased (linear and quadratic effects, P < 0.001) from 4.87 to 7.70 as dEB was increased from 0 to 500 mEq/kg (Table 3). Urine pH can change considerably as it provides a means to excrete excess H⁺ from the body and, thus, to stabilize the physiological state of the animal. Jensen (1994) reported that urine acidification through diet alteration could reduce the incidence of, and/or provide treatment for, urinary tract disease in cats. Dee et al. (1994) suggested manipulation of diets to lower pH of the urine and, thereby, decrease the likelihood of urinary track infections in sows. In our experiment, total bacterial concentrations in urine were decreased (linear effect, P < 0.03) with decreased dEB. This observation is promising because sows with minimal numbers of bacteria in their urinary tract would be considered less at risk for urinary tract disease.

Sow weight and backfat losses for d 0 to 10 and the overall 21-d lactation interval were not affected (P = 0.11) by dEB (Table 4). The lack of differences in BW and backfat change agree with our earlier observation that lack of differences in plasma urea N and urine creatinine suggest none of the dEB treatments used in our experiment had major effects on catabolic state of the sows.

For d 0 to 10 and overall, water usage was not affected (P = 0.40) by increasing dEB from 0 to 500 mEq/kg (Table 4). Escobosa et al. (1984) reported that water disappearance was increased for cows fed a diet with high (320 mEq/kg) dEB compared to a control diet with a dEB of 168 mEq/kg. However, the authors attributed the greater water usage to greater feed consumption and, in our experiment, just as ADFI was unaffected, neither was water usage.

Dove and Haydon (1994) reported no improvement in survivability or litter weight gain when dEB of the lactation diets were increased from 130 mEq/kg to 250 mEq/kg. Unfortunately, they did not investigate the effects of a decreased dEB. In contrast, Tilley (1997) reported greater survivability of piglets and increased litter weights when dEB of a corn-soybean meal-fishmeal-based lactation diet was decreased to -100 mEq/kg. In our experiment, a range in dEB of the lactation diets from 0 to 500 mEq/kg did not affect litter weight gain (P = 0.41). But litter size (linear effect, P < 0.04) and piglet survivability (linear effect, P < 0.05) during the first 10 d of lactation decreased with increased dEB (Table 4). Similarly, linear decreases occurred in number weaned (P < 0.01) and survivability (P < 0.02) to d 21 with increased dEB. Thus, our data are in agreement with those of Tilley (1997) and suggest that dEB lower than that found in a corn-soybean meal-based diet is beneficial during lactation.

As for the reason for increased piglet survivability with decreased dEB of the sow’s diet, we can hypothesize that this is a function of greater milk output. This would be supported by the observed increase in survivability for the first 10 d and the slight increase in litter weight gain with decreased dEB. Reduced bacterial counts in the sow’s urine suggest less exposure to bacterial challenge for the piglets as well.

Percentage of sows returning to estrus (P = 0.41), days to estrus (P = 0.15), and number born in the subsequent litter (P = 0.39) were not affected by increasing dEB from 0 to 500 mEq/kg (Table 4). These results indicate that a wide variation in dEB did not jeopardize the measurements of reproductive performance used in our experiment, but neither was it improved. In addition, milk pH (P = 0.13) and concentrations of fat (P = 0.32), lactose (P = 0.36), and CP (P = 0.44) were not affected by dEB (Table 5). Thus, it seems unlikely that the composition and, thus, nutritional value of sow’s milk can be manipulated by changing dEB of the diet. This is in agreement with the lack of differences in litter weight gain when dEB was increased from 0 to 500 mEq/kg.

	Implications

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	Footnotes

 
¹ Contribution no. 00-97-J from the Kansas Agric. Exp. Stn., Manhattan 66506.

² Animal care and use for the experiments reported herein were in accordance with the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (Consortium, 1988).

⁴ Church and Dwight Co., Inc., Princeton, NJ.

³ Correspondence: 244 Weber Hall (phone: 785-532-1230; fax: 785-532-7059; E-mail: jhancock{at}ksu.edu).

Received for publication September 13, 2002. Accepted for publication July 15, 2003.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by DeRouchey, J. M. Articles by Cao, H. Search for Related Content PubMed PubMed Citation Articles by DeRouchey, J. M. Articles by Cao, H.