Effect of Supplemental Sodium Chloride, Sodium Phosphate, or Hydrochloric Acid in Starter Pig Diets Containing Dried Whey 1,2

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1 Effect of Supplemental Sodium Chloride, Sodium Phosphate, or Hydrochloric Acid in Starter Pig Diets Containing Dried Whey 1,2 D. C. Mahan 3, E. A. Newton 4, and K. R. Cera 5 The Ohio State University and The Ohio Agricultural Research and Development Center, Columbus ABSTRACT: Three experiments involving a total of 606 pigs weaned at 23 ± 2 d of age were used to evaluate the effects of added dietary Na or Cl or both in combination (NaCl) on postweaning performance responses. A basal diet without added NaCl was formulated to 1.20% lysine using a corn-soybean protein mixture with 20% dried whey (C-SBP-DW) and was used in all experiments. The analyzed content of the basal diet for the three experiments averaged.19% Na,.37% Cl, and 1.37% K. In Exp. 1, NaCl was added to treatment diets at 0,.20,.40, and.60% at the expense of corn. The experiment was a randomized complete block (RCB) design conducted in 14 replicates using a total of 336 pigs (six pigs/ pen). The results demonstrated a linear ( P <.01) growth response during the 0- to 7-d and a quadratic ( P <.08) response during the 8- to 14-d period. Gain: feed ratio improved quadratically ( P <.08) for the 0- to 14-d period. In Exp. 2, Na 2 HPO 4 added to the C- SBP-DW basal diet provided supplemental Na levels of 0,.08,.16, and.24% Na to four treatment diets. The experiment was conducted in six replicates in a RCB design using a total of 144 pigs (six pigs/pen). The results demonstrated a linear ( P <.05) growth response during the 0- to 7-d period as Na level increased, but not thereafter, and an improved gain: feed ratio ( P <.05) for the 0- to 14-d period. In Exp. 3, Cl was added as HCl at 0,.05, or.10% Cl to the basal C-SBP-DW diet. The experiment was a RCB design conducted in six replicates using a total of 126 pigs (five or six pigs/pen between replicates). The results demonstrated a linear growth ( P <.01) and feed intake ( P <.08) response during the 0- to 7-d and the 0- to 14-d period to increasing levels of Cl. Feed intake also increased for the 0- to 7-d ( P <.08), and 8- to 14-d ( P <.05) periods. Stool looseness was unaffected by any of the dietary variables in the three experiments. These results suggest that the NRC (1988) recommendations for Na and Cl for young pigs ( 10 kg BW) may need to be increased. Key Words: Sodium, Chloride, Salt, Weaning, Pigs J. Anim. Sci : Introduction Current swine practices result in weaning pigs from 11 to 28 d of age at body weights that range from 4 to 8 kg. Pigs weaned at the younger ages and lighter body weights have a less mature gastrointestinal tract 1 Salaries and research support provided by state and federal funds appropriated to The Ohio Agric. Res. and Dev. Center, The Ohio State Univ., manuscript no Appreciation is expressed to S. Amos and K. Mays for data collection, F. Cihla and M. Watts for laboratory analyses, and M. Milligan for typing the manuscript. 3 To whom correspondence and reprint requests should be addressed: Anim. Sci. Dept., The Ohio State Univ., 2027 Coffey Road. 4 Present address: Newsham Hybrids (USA), Inc., Colorado Springs, CO Present address: Countrymark Coop., Inc., Indianapolis, IN Received August 16, Accepted February 8, (de Passille et al., 1989) and secrete lower quantities and different ratios of digestive enzymes (Graham et al., 1981; Sloat et al., 1985) compared with older, heavier weaned pigs. Because of their physiological immaturity, the initial diets provided to pigs postweaning are generally formulated using relatively high levels of milk by-products, one of the more common being dried whey. Dried whey added at 15 to 25% of the diet contains high mineral levels, particularly Na, K, and Cl (NRC, 1988). Because the osmotic electrolyte balance in the gut of young weanling pigs may be delicate (Hamilton and Roe, 1977), gastrointestinal upsets due to excessive dietary cations and(or) anions have been considered to be harmful to the weaned pig. Consequently, postweaning scours, which have frequently been encountered when such diets are fed, have been attributed to the high ash (i.e., 8.0%) content contributed from whey. Sodium and Cl requirements for weanling pigs have not been as well defined as for older swine. Chloride constitutes a portion of the gastric secretions, and the 1217

2 1218 MAHAN ET AL. ability of young pigs to synthesize HCl seems to be limited until 4 to 5 wk of age (Cranwell et al., 1976). The NRC (1988) recommends a total dietary level of.10% Na and.08% Cl for young pigs, which can be adequately met by the addition of.25% salt (NaCl) to the diet, discounting the contribution from the other dietary components. The addition of dried whey to the weanling pig diet supplies levels of Na, K, and Cl beyond that suggested by NRC (1988), and further supplementation with NaCl would seem unneeded. Therefore, the objectives of these experiments were to initially evaluate the effect of NaCl addition to starter pig diets that contain dried whey on performance and stool looseness responses and, second, because of the positive performance response to added salt in the first experiment, to further identify the growth response to added Na or Cl. Materials and Methods General. Crossbred ([Yorkshire Landrace] Duroc) pigs in the three experiments were weaned at 23 ± 2 d of age. Pigs were housed within replicate in either environmentally controlled double-decked nursery pens with expanded metal floors or in singledecked elevated nursery pens with rubber-coated expanded metal floors and electric heat pads (50% of floor surface area). All pens measured m and were equipped with one nipple waterer and a five-hole self-feeder. Environmental temperatures in the nurseries were established initially at approximately 28 C but adjusted gradually to 20 C by the end of the 35-d experimental period. Average fecal scores for pigs by pen were subjectively evaluated by the same individual once daily (1300 to 1400) from Monday through Friday for the 35-d postweaning period. Fecal scores were classified as firm (1), loose (2), or watery (3). Pig weights and pen feed intakes were measured weekly. Feed was provided for ad libitum intake during the 35-d trials, and animal weights and feed intake were measured weekly. Experiment 1. The first experiment evaluated the efficacy of added salt (NaCl) to a cereal grain-based diet with dried whey to determine whether supplemental NaCl levels would precipitate stool looseness during the course of the experiment, and to evaluate the effect of added salt on postweaning performance responses. The basal diet consisted of a corn-soybean protein (soybean meal, soy protein concentrate) mixture with 20% dried whey ( C-SBP- DW) formulated to a 1.20% lysine level. The other dietary nutrients met or exceeded NRC (1988) requirement levels. The basal diet is presented in Table 1. Neither Na nor Cl was supplemented to the basal diet, but by analysis the indigenous content of the diet contained.20% Na,.35% Cl, and 1.35% K. The other three treatment diets were subsequently supplemented with.20,.40, and.60% NaCl at the expense of corn (diets not presented). A total of 336 pigs were allotted on the basis of weight, litter, and sex in a randomized complete block ( RCB) design in 14 replicates containing six pigs per pen at four different time periods. Experiment 2. Because the addition of NaCl to the basal diet in Exp. I resulted in a positive growth response to added NaCl, a second experiment was conducted to determine whether the beneficial Table 1. Percentage composition of experimental diets (as fed) Exp. 1,3 Exp. 2 Ingredient.20% Na.18% Na.26% Na.34% Na.42% Na Corn Soybean meal (44% CP) Soy protein concentrate a Edible-grade dried whey Dicalcium phosphate Sodium phosphate b HCl c + Limestone Se premix d Trace mineral salt e Vitamin mix f Antibacterial agent g a Soybean protein concentrate was an extruded soy protein (Profine E; Central Soya, Decatur, IN). b Sodium phosphate contained 32% Na and 21% P. c Hydrochloric acid was diluted with water (1:1, vol/vol) and premixed with ground corn at the appropriate dietary level prior to adding to the feed mixer in Exp. 3. Analysis of the solution was 20% chloride. d Sodium selenite in a limestone carrier provided.3 ppm Se. e Supplied per kilogram diet: 10 mg of Cu; 100 mg of Fe;.2 mg of I; 40 mg of Mn; 120 mg of Zn; and 2.77 g of NaCl. f Supplied per kilogram diet: 4,000 IU of vitamin A; 300 IU of vitamin D 3 ; 15 mg of d-pantothenic acid; 12 mg of niacin;.3 mg of folacin;.2 mg of d-biotin; 20 mg of vitamin B 12 ; 1.25 g of choline, and 66 mg of butylated hydroxytoluene as an antioxidant. g Supplied 55 mg of carbadox per kilogram diet.

3 SODIUM AND CHLORIDE SUPPLEMENTATION 1219 response to added salt was attributable to Na. The C- SBP-DW basal diet from Exp. I served as the negative control and by analysis contained.18% Na,.35% Cl, and 1.50% K. Three additional treatment diets were supplemented with Na 2 HPO 4 (32% Na, 21%P) at three.25% (i.e.,.08% Na) increments to achieve total dietary Na levels of.26,.34, and.42% (Table 1). Limestone and dicalcium phosphate levels were subsequently adjusted to maintain total dietary Ca and P levels of.90 and.70%, respectively. A total of 144 pigs were allotted on the basis of weight, litter, and sex to a RCB design in six replicates over two different time periods; each pen contained six pigs. Experiment 3. A third experiment was conducted to evaluate the efficacy of added Cl to a C-SBP-DW basal diet. The basal diet of Exp. I and Exp. II was used in this experiment and by analysis contained.20% Na,.40% Cl, and 1.25% K (Table 1). Concentrated HCl was diluted 1:1 (vol:vol) and added to two treatment diets such that the Cl content was increased by.05 and.10% to achieve total dietary levels of.45 and.50% Cl, respectively. The diluted HCl was premixed with ground corn before it was added to the mixer. A total of 126 pigs were allotted on the basis of weight, litter, and sex to a RCB-designed experiment conducted in seven replicates at three different time periods. Analyses. Diets were composited by treatment group, wet-ashed, and analyzed for Na and K by the inductively coupled photometer method (AOAC, 1995). Chloride was analyzed by the AOAC (1995) method using a chloridometer (Model , Buchler-Cotlove, Saddle Brook, NJ). The data of the three experiments were analyzed using the GLM procedure of SAS (1985). Pen fecal scores were averaged for each week of the trial. Nursery type and time period effects were included in the statistical model. In all experiments, pens were considered the experimental unit. All performance responses for the dietary levels of test ingredients were evaluated by regression analysis with the data reported as least squares means. Results The addition of NaCl to the basal C-SBP-DW diet in Exp. 1 resulted in daily gains that increased linearly ( P <.01) for d 0 to 7 and quadratically ( P <.08) during the period from 8 to 14 d postweaning (Table 2). For the combined 0- to 14-d period, pig gains improved quadratically ( P <.07) and seemed to reach a plateau at the.44% Na and.51% Cl levels. No growth response to added NaCl occurred during the 15- to 35-d period. Feed intakes for each weekly period and for the 15- to 35-d period were similar for all treatment groups. Gain:feed ratio was improved when dietary NaCl level increased during the 0- to 7-d ( P <.01) and for the combined 0- to 14-d ( P <.08) period, but not for the 15- to Table 2. Effect of supplemental sodium chloride to cereal grain diets with added dried whey for weanling pigs (Exp. 1) NaCl level, % 0 b Total Na, %: Item a Total Cl, %: SEM Daily gain, g 0 to 7 d c 8 to 14 d d 0 to 14 d e 15 to 35 d Daily feed intake, g 0 to 7 d to 14 d to 14 d to 35 d Gain:feed ratio 0 to 7 d c 8 to 14 d to 14 d d 15 to 35 d a Fourteen replicates were conducted (84 pigs/treatment group). Pigs were weaned at 23 ± 2 d of age and averaged 6.63 kg BW. Chemical analysis of the basal diet (as-fed basis) averaged.20% Na, 1.35% K, and.35% Cl. Linear response ( P <.01). Quadratic response ( P <.08). Quadratic response ( P <.07).

4 1220 MAHAN ET AL. 35-d period. Fecal looseness scores averaged 1.1 for all treatment groups and were unaffected by dietary treatment for any week of the experiment (data not presented). Because the Na and Cl levels in our basal diet were two- and fourfold times the current NRC (1988) recommendations, respectively, and because a growth response resulted from the NaCl addition to the C- SBP-DW diet in Exp. 1, the second experiment was designed to evaluate the effect of supplemental Na while maintaining a constant level of Cl in the diet. Added Na from sodium phosphate improved daily gains linearly ( P <.05) during the 0- to 7-d period but not for the 8- to 14-d ( P >.15) or for the 15- to 35-d ( P >.15) periods (Table 3). Feed intakes for the 0- to 14- and 15- to 35-d periods were not affected by Na supplementation. Gain:feed ratios improved linearly for the 0- to 7-d ( P <.05) and quadratically during the 0- to 14-d period ( P <.05). Although there was an apparent improvement in feed efficiency during the 15- to 35-d period, the response was not significant ( P >.15). Fecal scores averaged 1.1 and were similar between all treatment groups for each week of the trial (data not presented). In Exp. 3 the addition of HCl resulted in improved daily gains ( P <.01), feed intakes ( P <.08), and gain: feed ratios ( P <.08) during the initial 7-d postweaning period (Table 4). From d 8 to 14 daily gains ( P <.08), feed intakes ( P <.05), and gain:feed ratios improved as Cl level increased, but the feed efficiency response was not significant ( P >.15). Both daily gains ( P <.01) and feed intakes ( P <.08) were higher for the 0- to 14-d period as dietary Cl level increased. Although there was a numerical improvement in the gain:feed ratio during the 0- to 14-d period, the results were not significant ( P >.15). From 15 to 35 d postweaning daily gains and feed intakes were not improved by the addition of HCl. The apparent improvement in gain:feed ratio from 15 to 35 d postweaning as dietary Cl level increased was not significant ( P =.11). Fecal scores averaged 1.1 and were similar between treatment groups (data not presented). Discussion The results from these three experiments suggest that there was no detrimental effect of the high indigenous level of Na or Cl contributed from dried whey in the basal diet and that additional dietary NaCl did not produce any digestive disturbances or stool looseness during the 35-d trial period. In fact, supplemental NaCl or the addition of either Na or Cl independently added to the cereal grain basal diet containing dried whey demonstrated improved pig gains and feed efficiency responses at least during the initial 14 d postweaning. The largest and most consistent response occurred during the initial week postweaning, a lesser response during the second week, and no response thereafter. Although indigenous dietary levels of Na or Cl in the basal diet in the three experiments had already exceeded NRC (1988) recommendations, our results suggest that the Table 3. Effect of supplemental sodium phosphate to cereal grain diets with added dried whey for weanling pigs (Exp. 2) a Sodium phosphate level, % 0 b Item Total Na, % SEM Daily gain, g 0 to 7 d c 8 to 14 d to 14 d to 35 d Daily feed intake, g 0 to 7 d to 14 d to 14 d to 35 d Gain:feed ratio 0 to 7 d c 8 to 14 d to 14 d c 15 to 35 d a Seven replicates were conducted (49 pigs/treatment group). Pigs were weaned at 23 ± 2 d of age and averaged 6.93 kg BW. Analysis of the basal diet (as fed basis) was.18% Na, 1.50% K, and.35% Cl. Linear response ( P <.05).

5 SODIUM AND CHLORIDE SUPPLEMENTATION 1221 Table 4. Effect of supplemental hydrochloric acid to cereal grain diets with added dried whey for weanling pigs (Exp. 3) a Added Cl, % b Item Total Cl, %.40 c SEM Daily gain, g 0 to 7 d d 8 to 14 d e 0 to 14 d d 15 to 35 d Daily feed intake, g 0 to 7 d e 8 to 14 d f 0 to 14 d e 15 to 35 d Gain:feed ratio 0 to 7 d e 8 to 14 d to 14 d to 35 d a Seven replicates were conducted (42 pigs/treatment group). Pigs were weaned at 23 ± 2 d of age and averaged 5.96 kg BW. Hydrochloric acid was added to the diets at various levels to provide the supplemental level of Cl. Chemical analysis of the basal diet (as-fed basis) was.20% Na, 1.25% K, and.40% Cl. Linear response ( P <.01). Linear response ( P <.08). Linear response ( P <.05). dietary requirements for both nutrients are above the.10% Na and.08% Cl level for young pigs weighing < 10 kg BW. One reason for this higher dietary Cl requirement may be that young pigs do not secrete adequate quantities of HCl during early life. Upon weaning, the secretion of this acid is still relatively low (Schnabel as cited by Bolduan et al., 1988). The value of HCl in initiating protein digestion in the stomach occurs by the activation of pepsinogen. Stomach HCl production and the resulting ph within this organ ranges widely for both weaned and unweaned pigs. The multiplication of Lactobacilli spp. in the stomach of nursing pigs and the subsequent production of lactic acid can suppress HCl production (Cranwell et al., 1968, 1976). Large intakes of feed can also reduce HCl production (Kidder and Manners, 1978). Although dried whey contains relatively high levels of Na and Cl, which should meet the pigs requirement (NRC, 1988), this milk by-product can neutralize free acid more than cereal grain proteins (P.G. Lawlor, personal communication). Young pigs may therefore secrete inadequate HCl from gastric secretions and the inclusion of dried whey and other dietary proteins and minerals may buffer the low amount of HCl produced from gastric secretions. Consequently, the addition of dietary NaCl or HCl would then be an avenue that could supply a needed source of Cl for pepsinogen activation, which could improve protein digestion. The combination of these factors in the young pig may increase the physiological need for Cl, at least until the gastric secretion of this acid increases. The improvement in pig gains in our experiments, and particularly the improvement in the gain:feed ratio, implies an improvement of nutrient availability, most probably by enhanced protein digestibility. The results of our experiments also suggest that the dietary Na requirement is higher for the young pig than current NRC (1988) recommendations. The reason for this is unclear, except that the lower acidic stomach conditions from higher level Cl are subsequently neutralized by bicarbonate upon entrance to the small intestine, Na being the positive ion with bicarbonate. The Na pump is also essential for the absorption of amino acids and carbohydrates from the lumen of the intestinal tract. Our results thus imply a need for higher dietary levels of Na for the weanling pig, during the first 7 and perhaps 14 d postweaning. A previous study of weanling pigs (Honeyfield and Froseth, 1985) demonstrated that, when weanling pigs were fed a diet based on a corn-soybean meal-corn gluten meal, growth rate was maximal at dietary levels of.11% Na and.10% Cl. Their report, however, indicated that the pigs were fed a constant diet for 1 wk postweaning before being fed their experimental diets. Our data demonstrated the largest relative growth and feed efficiency responses to higher dietary Na and Cl levels were achieved during the initial 7 d postweaning. This suggests that the conclusions of Honeyfield and Froseth (1985) may not reflect the most critical time that weaned pigs may respond to

6 1222 MAHAN ET AL. supplemental Na and Cl. Consequently, our results suggest that a higher level of Na and Cl should be provided in the diets of weaned pigs to enhance growth and feed efficiency responses, particularly during the initial 14 d postweaning. Implications The high levels of Na and Cl in dried whey do not have an apparent detrimental effect on gastrointestinal osmotic balance, but rather the addition of NaCl to a diet with dried whey resulted in improved postweaning performance. Subsequent experiments demonstrated that the dietary Na requirement may be higher during the initial week and that the Cl dietary requirement may be higher during the initial 14 d postweaning than the levels recommended by NRC (1988). Pig performance responses to supplemental Na or Cl after 14 d postweaning were not demonstrated. Literature Cited AOAC Official Methods of Analysis (16th Ed.). Association of Official Analytical Chemists, Arlington, VA. Bolduan, G., H. Jung, E. Schnabel, and R. Schneider Recent advances in the nutrition of weaner piglets. Pig News Info. 9: 381. Cranwell, P. D., D. E. Noakes, and K. J. Hill Observations on the stomach contents of the suckling pig. Proc. Nutr. Soc. 27, 26A (Abstr.). Cranwell, P. D., D. E. Noakes, and K. J. Hill Gastric secretion and fermentation in the suckling pig. Br. J. Nutr. 36:71. de Passille, A.-M.B., G. Pelletier, J. Ménard, and J. Morisset Relationships of weight gain and behavior to digestive organ weight and enzyme activities in piglets. J. Anim. Sci. 67:2921. Graham, P. L., D. C. Mahan, and R. G. Shields, Jr Effect of starter diet and length of feeding regimen on performance and digestive enzyme activity of 2-week old weaned pigs. J. Anim. Sci. 53:299. Hamilton, D. L., and W. E. Roe Electrolyte levels and net fluid and electrolyte movements in the gastrointestinal tract of weanling swine. Can. J. Comp. Med. 41:241. Honeyfield, D. C., and J. A. Froseth Effects of dietary sodium and chloride on performance, plasma electrolytes and plasma basic amino acids in young pigs. J. Nutr. 115:1366. Kidder, D. E., and M. J. Manners Conditions in the lumen ph. In: Digestion in the Pig. p 39. Kingston Press, Bath, Canada. NRC Nutrient Requirements of Swine (9th Ed.). National Academy Press, Washington, DC. SAS SAS User s Guide: Statistics (Version 5 Ed.). Inst. Inc., Cary, NC. Sloat, D. A., D. C. Mahan, and K. L. Roehrig Effect of pig weaning weight on postweaning body composition and digestive enzyme development. Nutr. Rep. Int. 31:627.