Effects of Increasing Chloride Concentrations on Growth Effects of Increasing Chloride Concentrations on Growth Performance of 15-to 25-lb Nursery Pigs Performance of 15-to 25-lb Nursery Pigs

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Introduction
Mahan et al. 3,4 observed that dietary salt addition was positively correlated to ADG and F/G in nursery pigs.When analyzing dietary Cl concentrations independently, Mahan et al. 3 observed that ADG improved up to a total dietary Cl concentration of 0.50% in diets containing dried whey, though in a second study, the optimal Cl concentration in diets containing spray-dried animal plasma was 0.32%. 4The NRC 2 requirement estimate for 15 to 24 lb pigs is 0.35% and 0.45% for Na and Cl, respectively.In a previous study, Shawk et al. 5 observed that pigs fed a diet that was formulated to meet NRC 2 estimates for Na (0.37%) and exceeded the Cl (0.60%) requirement estimate had improved ADG and ADFI compared to pigs fed a diet that was deficient in both Na (0.18) and Cl (0.36%).Pigs that were fed a diet with added sodium bicarbonate and potassium chloride, 0.37% Na and 0.35% Cl were intermediate.The pigs fed the sodium bicarbonate and potassium chloride diet could have been intermediate in growth performance due to the source of the Na and Cl or the diets may have simply been deficient in Cl since the NRC 2 requirement estimate is 0.45%.Therefore, the objective of this study was to determine the dietary Cl requirement of nursery pigs weighing 15 to 25 lb when diets were formulated to meet the Na requirement estimate.

Procedures
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used in this experiment.The study was conducted at the Kansas State University Swine Teaching and Research Center in Manhattan, KS.Each pen was equipped with a 4-hole, dry self-feeder and a nipple waterer to provide ad libitum access to feed and water.
A total of 300 pigs (initially 15.5 lb; Line 241 × 600; DNA, Columbus, NE) were used in a 21-d growth trial.Pigs were weaned at approximately 21 d of age and moved to the nursery.Pigs were randomly allotted to pens of 5 based on their initial BW.Pigs were fed a common diet (0.33% Na and 0.77% Cl) for 7 d after weaning.On d 7 after weaning, considered d 0 in the trial, pens were randomly assigned to 1 of 6 dietary treatments with 10 replications per treatment.Experimental treatments included a control diet containing 0.33% Na and 0.55% Cl provided by 0.78% added salt or 5 diets with 0.33 % Na, and added potassium chloride to provide 0.09, 0.21, 0.32, 0.45, or 0.55% Cl.Treatment diets were fed for 14 d with a common diet (0.18% Na and 0.49% Cl) fed from d 14 to 21. Pens of pigs were weighed and feed disappearance was recorded on d 0, 7, 14, and 21 to determine ADG, ADFI, and F/G.All experimental diets were manufactured at the Kansas State University O.H. Kruse Feed Technology Innovation Center, Manhattan, KS.Dietary treatments were cornsoybean meal-based with 7.2% crystalline lactose and were fed in meal form (Table 1).
3 Mahan, D. C., E. A. Newton, and K. R. Cera.1996.Effect of supplemental sodium chloride, sodium phosphate, or hydrochloric acid in starter pig diets containing dried whey.J. Anim. Sci. 74:1217-1222. 4 Mahan, D. C., T. D. Wiseman, E. Weaver, and L. Russell.1999.Effect of supplemental sodium chloride and hydrochloric acid added to initial starter diets containing spray-dried blood plasma and lactose on resulting performance and nitrogen digestibility of 3-week-old weaned pigs.J. Anim.Sci.77:3016-3021.Salt, potassium chloride, or sodium bicarbonate replaced sand in the diets to provide the different dietary treatments.All diets were formulated to have a dietary Na concentration of 0.33% with either the inclusion of salt at 0.78% or sodium bicarbonate at 23 lb/ton.Diet samples were collected at the feed mill, subsampled, and submitted to Ward Laboratories, Inc., (Kearney, NE) and Cumberland Valley Analytical Service, (Maugansville, MD) for analysis of DM, CP, Na, and Cl (Table 2).
Data were analyzed as a randomized complete block design using PROC GLIMMIX in SAS version 9.4 (SAS Institute, Inc., Cary, NC) with pen as the experimental unit.Linear and quadratic polynomials were used to evaluate increasing added Cl. Means of the 0.55% Cl treatment and the control diet were separated using the least square mean method.Results were considered significant at P ≤ 0.05 and marginally significant between P > 0.05 and P ≤ 0.10.

Results and Discussion
Chemical analysis indicated that the dietary Na concentration of the treatment diets was similar to formulated values, except for the 0.55% Cl diet, which analyzed at a slightly greater concentration than expected (Table 2).Dietary Cl concentrations of the treatment diets were similar to formulated values, except for the 0.55% Cl diet and control diet which had slightly lower Cl concentrations than formulated but within acceptable analytical variation.
From d 0 to 14, ADG, ADFI, and F/G improved (quadratic, P < 0.05) as dietary Cl concentration increased from 0.09 to 0.32% with no further benefits observed thereafter (Table 4).Pigs fed the 0.55% Cl diet had increased (P < 0.05) ADFI compared with pigs fed the control diet with 0.55% Cl from added salt.Pigs fed the 0.55% Cl diet tended (P = 0.53) to have poorer F/G than pigs fed the control diet with added salt.Pigs fed the control diet and the 0.55% Cl diet had similar ADG.
From d 14 to 21, when pigs were fed a common diet, compensatory gain was observed for pigs previously fed the low chloride diet.Average daily gain decreased (linear, P = 0.045) and ADFI increased (linear, P = 0.033) with increasing dietary Cl previously fed from d 0 to 14. Pigs previously fed increasing Cl had poorer (quadratic, P = 0.020) F/G.Pigs previously fed the 0.55% Cl diet had greater (P = 0.009) ADFI and tended (P = 0.059) to have poorer F/G than pigs previously fed the control diet with 0.78% added salt.There was no evidence of difference in ADG between pigs previously fed the control diet or the 0.55% Cl diet.
For the overall experimental period that included the treatment and common periods (d 0 to 21), ADG increased (quadratic, P = 0.002) as dietary Cl increased from 0.09 to 0.32% with no further benefits observed thereafter.Average daily feed intake increased (linear, P = 0.002) as dietary Cl increased.Pigs fed the 0.55% Cl diet had greater (P < 0.05) ADFI but poorer F/G than pigs fed the control diet with 0.55% Cl from added salt with no evidence of difference between these two diets for ADG.
On d 14 and 21, BW increased (quadratic, P = 0.006) as dietary Cl increased from 0.09 to 0.32%, with no further benefits observed thereafter.Overall, there was no difference in BW between the control diet and the 0.55% dietary Cl diet.
In conclusion, results of this study would indicate a dietary Cl concentration of 0.32% optimized ADG, ADFI, and F/G of pigs from approximately 15 to 25 lb.A Cl concentration of 0.32% is slightly lower than the NRC 2 current requirement estimate of 0.45%.A Cl concentration of 0.32% would also be lower than the optimal Cl concentration reported by Mahan et al., 3 who suggested a dietary Cl requirement of 0.50% for 13 to 31 lb pigs, but would agree with the results of another study, which indicated the Cl requirement for 13 to 26 lb pigs was 0.32%. 4When comparing the 0.55% Cl diet to the control diet, there was no evidence of difference for ADG, but pigs fed the control diet with added salt had a lower ADFI and tended to have improved F/G.This would possibly suggest that source of the Na and Cl ions influences growth performance and may explain why Shawk et al. 5 observed an intermediate growth response to a diet containing sodium bicarbonate and potassium chloride when compared to diets containing added salt.Results of this study indicates the minimum dietary Cl requirement for 15 to 25 lb pigs is 0.32%.

Table 3 .
Chemical analysis of experimental diets (as-fed basis) 1 1 Samples were collected at the mill, homogenized, and then subsampled for analysis. 2les were submitted to Ward Laboratories (Kearney, NE) for proximate analysis.3CumberlandValleyAnalyticalService (Maugansville, MD).4Ward Laboratories (Kearney, NE).

Table 4 .
Effects of increasing chloride for 15 to 25 lb nursery pigs 1