Effects of Dietary Ca and P Concentrations on Growth Performance of 13- to 25-lb Pigs

A total of 360 nursery pigs (PIC 1050 × 280, initially 13.3 ± 2.39 lb) were used in a 45-d growth study to determine the effects of feeding 2 standardized total tract digestible (STTD) P and 3 Ca concentrations on growth performance. In a completely randomized design, pens of pigs (10 pigs per pen, 6 pens per treatment) were allotted randomly to 1 of 6 dietary treatments. Dietary treatments were arranged in a 2 × 3 factorial, with 2 levels of STTD P (at or above NRC requirement estimates) and 3 levels of Ca (0.65, 0.90, and 1.20%). Diets formulated to meet NRC P requirement estimates contained 0.45 or 0.40% STTD P in phases 1 and 2, respectively, and diets formulated to exceed NRC P requirements contained 0.56 or 0.52% STTD P in phases 1 and 2, respectively. Diets were provided in 3 phases, with pigs fed experimental diets during phase 1 (d 0 to 10) and phase 2 (d 10 to 24), followed by a common phase 3 diet from d 24 to 45. During the treatment period (d 0 to 24), no Ca × P interactions were observed for ADG and ADFI. Increasing Ca concentration decreased (linear, P = 0.006) ADG, but did not affect ADFI. Feeding high concentrations of STTD P tended to increase (P = 0.084) ADG, but did not affect ADFI, compared with pigs fed STTD P levels recommended by NRC. An interactive effect between Ca and STTD P was observed for F/G (P = 0.018). When diets contained NRC levels of STTD P, pigs fed 1.20% Ca had poorer (P < 0.05) F/G than those fed 0.65 or 0.90% Ca; however, when high levels of STTD P were fed, the dietary Ca concentrations did not affect F/G. Day 24 BW decreased (linear, P = 0.006) with increasing Ca concentrations, regardless of the STTD P levels in diets. From d 24 to 45, when all pigs received a common phase 3 diet, no interactive or main effects of Ca and STTD P concentrations were observed for ADG, ADFI, or final BW. However, pigs previously fed increasing concentrations of Ca had improved (linear, P = 0.003) F/G regardless of dietary STTD P content. As a result of this compensatory gain, no treatment effects were observed for the overall growth performance. In conclusion, excess dietary Ca impairs ADG and F/G of nursery pigs, especially in low P content diets. The STTD P levels estimated by NRC meet the requirement of 13to 25-lb pigs when diets contain low Ca concentrations but are deficient when diets contain more than 0.90% Ca.


Summary
A total of 360 nursery pigs (PIC 1050 × 280, initially 13.3 ± 2.39 lb) were used in a 45-d growth study to determine the effects of feeding 2 standardized total tract digestible (STTD) P and 3 Ca concentrations on growth performance.In a completely randomized design, pens of pigs (10 pigs per pen, 6 pens per treatment) were allotted randomly to 1 of 6 dietary treatments.Dietary treatments were arranged in a 2 × 3 factorial, with 2 levels of STTD P (at or above NRC3 requirement estimates) and 3 levels of Ca (0.65, 0.90, and 1.20%).Diets formulated to meet NRC 3 P requirement estimates contained 0.45 or 0.40% STTD P in phases 1 and 2, respectively, and diets formulated to exceed NRC 3 P requirements contained 0.56 or 0.52% STTD P in phases 1 and 2, respectively.Diets were provided in 3 phases, with pigs fed experimental diets during phase 1 (d 0 to 10) and phase 2 (d 10 to 24), followed by a common phase 3 diet from d 24 to 45.During the treatment period (d 0 to 24), no Ca × P interactions were observed for ADG and ADFI.Increasing Ca concentration decreased (linear, P = 0.006) ADG, but did not affect ADFI.Feeding high concentrations of STTD P tended to increase (P = 0.084) ADG, but did not affect ADFI, compared with pigs fed STTD P levels recommended by NRC. 3 An interactive effect between Ca and STTD P was observed for F/G (P = 0.018).When diets contained NRC 3 levels of STTD P, pigs fed 1.20% Ca had poorer (P < 0.05) F/G than those fed 0.65 or 0.90% Ca; however, when high levels of STTD P were fed, the dietary Ca concentrations did not affect F/G.Day 24 BW decreased (linear, P = 0.006) with increasing Ca concentrations, regardless of the STTD P levels in diets.From d 24 to 45, when all pigs received a common phase 3 diet, no interactive or main effects of Ca and STTD P concentrations were observed for ADG, ADFI, or final BW.However, pigs previously fed increasing concentrations of Ca had improved (linear, P = 0.003) F/G regardless of dietary STTD P content.As a result of this compensatory gain, no treatment effects were observed for the overall growth performance.In conclusion, excess dietary Ca impairs ADG and F/G of nursery pigs, especially in low P content diets.The STTD P levels estimated by NRC 3 meet the requirement of 13-to 25-lb pigs when diets contain low Ca concentrations but are deficient when diets contain more than 0.90% Ca.

Introduction
Appropriate dietary Ca and P concentrations are essential for pig growth performance.The total Ca and STTD P requirements estimated by NRC 3 are 0.86 and 0.45%, respectively, for 13-to 15-lb pigs; and 0.79 and 0.40%, respectively, for 15-to 25-lb pigs.In a previous study, we demonstrated that adding phytase improved pig growth performance when diets contained a STTD P level similar to NRC 3 requirement. 4This finding suggests that the STTD P requirement may have been slightly underestimated for pigs of this weight range.In addition, we also observed that feeding excess dietary Ca decreased pig growth performance when diets were deficient in P, but not in pigs fed high P diets.Therefore, the objective of this study was to determine the effects of feeding 2 STTD P levels, either at or above the NRC 3 requirement, in combination with 3 different Ca concentrations on growth performance of nursery pigs.

Procedures
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used in the experiment.The study was conducted at the Cooperative Research Farm's Swine Research Nursery (Kalmbach Feeds, Inc., Sycamore, OH).Each pen (5 × 6 ft 2 ) had completely slatted metal floors and was equipped with a 4-hole stainless-steel feeder and a nipple-cup waterer.Pigs were allowed ad libitum access to feed and water throughout the experiment.
A total of 360 weaned pigs (PIC 1050 × 280) with initial BW of 13.3 ± 2.39 lb were housed in 36 pens with 10 pigs per pen.Upon arrival, pigs were individually weighed and assigned to pens to achieve balanced pen weights.Pens of pigs were then allotted to 1 of 6 dietary treatments (Tables 1 and 2) in a completely randomized manner.The dietary treatments were arranged in a 2 × 3 factorial, with 2 levels of STTD P (at or above NRC 3 requirement estimates) and 3 levels of total Ca (0.65, 0.90, and 1.20%).
Diets formulated to meet NRC 3 P requirement contained 0.45 and 0.40% STTD P in phases 1 and 2, respectively; diets formulated to exceed NRC 3 P requirement (>NRC) contained 0.56 and 0.52% STTD P in phases 1 and 2, respectively.Pigs were fed in 3 phases, with the experimental diets provided in phase 1 (d 0 to 10) and 2 (d 10 to 24).A common phase 3 diet was then fed to all pigs from d 24 to 45. Phase 1 diets were prepared in pellet form and phases 2 and 3 diets were provided in meal form.Pigs and feeders were weighed on d 0, 10, 24, and 45 to determine ADG, ADFI, and F/G.Inc., Cary, NC) in a completely randomized design with pen as the experimental unit.
The treatment effects were analyzed as a 2 × 3 factorial, with main effects of Ca and P and their interaction.Four single degree-of-freedom contrasts were performed to test the linear and quadratic effects of increasing Ca and their interactions with P concentration.Means were reported as least-squares means and were separated by the PDIFF option with a Tukey-Kramer adjustment.Results were considered significant at P < 0.05 and marginally significant at 0.05 < P < 0.10.

Results and Discussion
Analyzed Ca and P concentrations of dietary treatments were similar to calculated values and followed similar patterns as the designed treatment structure (Tables 1 and 2).
During phase 1 (d 0 to 10), no Ca × P interactions were observed for any growth responses.Calcium and STTD P concentrations did not affect ADG or d 10 BW.However, increasing Ca concentration increased (linear, P = 0.014) ADFI and worsened (P = 0.014) F/G.Feeding pigs 0.56% STTD P tended to worsen (P = 0.088) F/G compared with those fed diets containing 0.45% STTD P, with the response being driven by a poor F/G of pigs fed 0.90 or 1.20% Ca with 0.56% STTD P.
During phase 2 (d 10 to 24), Ca × P interactions were observed for ADG (P = 0.088) and F/G (P = 0.002), but not for ADFI or BW.Pigs fed 1.20% Ca had decreased (P < 0.05) ADG and poorer (P < 0.05) F/G compared with those fed 0.65 and 0.90% Ca when diets contained 0.40% STTD P; however, this detrimental effect of high Ca was not observed in pigs fed 0.52% STTD P. Average daily feed intake was not affected by dietary Ca or STTD P concentrations.Day 24 BW was decreased (linear, P = 0.006) by increasing Ca concentrations regardless of the STTD P levels in diets.
When combining the treatment periods (d 0 to 24), no Ca × P interactions were observed for ADG and ADFI.Increasing Ca concentration decreased (linear, P = 0.006) ADG, but had no effect on ADFI.Similarly, feeding >NRC 3 levels of STTD P tended to increase (P = 0.084) ADG, but did not affect ADFI, compared with pigs fed NRC 3 levels of STTD P. Concentrations of Ca and STTD P had an interactive effect on F/G (P = 0.018).When diets contained NRC 3 levels of STTD P, pigs fed 1.20% Ca had poorer (P < 0.05) F/G than those fed 0.65 and 0.90% Ca; however, when >NRC 3 levels of STTD P were fed, the dietary Ca concentrations did not affect F/G.
High Ca concentration has been demonstrated to decrease P digestibility and absorption by forming a Ca-P complex. 5,6In a previous study, 4 we observed that feeding excess Ca (1.05 vs. 0.58%) decreased pig growth performance when diets were deficient in P, but not in adequate P diets (0.45% STTD P during phases 1 and 2).Results from the present study suggest that feeding high Ca diets worsens F/G independent of STTD P concentrations in phase 1.However, in phase 2, the detrimental effects of high Ca on ADG and F/G were only observed in pigs fed 0.40% STTD P (NRC) but not for pigs that received 0.52% STTD P (> NRC).It is possible that 0.40% STTD P just met, or was marginally below, the requirement of pigs during phase 2, which resulted in a P deficiency when high Ca was added to the diets.This marginal deficiency in STTD P was also supported by the observation that feeding high levels of STTD P (>NRC) tended to improve ADG from d 0 to 24.
From d 24 to 45, all pigs received a common phase 3 diet.No interactive or main effects of Ca and STTD P concentrations were observed for ADG, ADFI, or final BW.However, pigs previously fed increasing dietary Ca had improved (linear, P = 0.003) F/G regardless of the STTD P content previously fed in phases 1 and 2 diets.As a result of this compensatory gain, overall (d 0 to 45) growth responses were not affected by the Ca and P concentrations fed during phases 1 and 2.
In summary, feeding excess dietary Ca impairs ADG and F/G of nursery pigs, especially when diets contain low P content.The STTD P levels estimated by NRC 3 meet the requirement of 13-to 25-lb pigs when diets contain low Ca concentrations; however, caution is needed when NRC 3 P requirement estimates are applied to diets containing more than 0.90% Ca.  2 STTD = standardized total tract digestible.
Agricultural Experiment Station and Cooperative Extension Service 1 Effects of Dietary Ca and P Concentrations on Growth Performance of 13-to 25-lb Pigs 1 F. Wu, M.D. Tokach, J.M. DeRouchey, S.S. Dritz, 2 J.C. Woodworth, and R.D. Goodband The Ca and P content for ingredients used in diet formulation were from a previous study 4 conducted in the same research facility.Complete diet samples were obtained and delivered to Kansas State University Swine Laboratory and stored at -4°F until analysis.Feed samples were analyzed for DM, CP, ether extract, Ca, and P at Ward Laboratories, Inc. (Kearney, NE).Concentrations of Ca and P were also analyzed at Cumberland Valley Analytical Services Inc. (Maugansville, MD) and Midwest Laboratories (Omaha, NE).The means of analyzed nutrient values are presented in Tables1 and 2.

Table 3 .
Effects of Ca and P concentrations on growth performance of nursery pigs 1 A total of 360 barrows and gilts (PIC 1050 × 280, Hendersonville, TN) with initial BW of 13.3 ± 2.39 lb were used in a 45-d trial with 10 pigs per pen and 6 replications (pen) per treatment. 1