Effects of Dietary P Concentrations in Response to Increasing Dietary Ca Concentrations on Growth Performance of Nursery Pigs.

A total of 360 pigs (initially 6.0±1.08 kg BW) were used in a 45-d study to determine the effects of 2 standardized total tract digestible (STTD) P concentrations on growth performance of nursery pigs fed increasing dietary Ca. In a completely randomized design, pens of pigs (6 pens/treatment) were randomly allotted to 1 of 6 dietary treatments. Dietary treatments were arranged in a 2×3 factorial with main effects of STTD P (at or above NRC, 2012 recommended levels) and total Ca (0.65, 0.90, and 1.20%). Experimental diets were fed during phase 1 (d 0 to 10) and 2 (d 10 to 24), followed by a common phase 3 diet from d 24 to 45. Diets formulated to meet NRC (2012) P requirements contained 0.45 or 0.40% STTD P in phases 1 and 2, respectively. Diets exceeding NRC (2012) P requirements contained 0.56 or 0.52% STTD P in phases 1 and 2, respectively. 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 higher STTD P marginally increased (P=0.084) ADG, but did not affect ADFI, compared with pigs fed STTD P levels suggested by NRC (2012). When diets contained NRC (2012) levels of STTD P, pigs fed 1.20% Ca had lower (P<0.05) G:F than those fed 0.65 or 0.90% Ca; however, when high levels of STTD P were fed, G:F was not affected by the dietary Ca concentrations (Ca×P interaction, P=0.018). When common diets were fed from d 24 to 45, no interactive or main effects of Ca and STTD P were observed for ADG, ADFI, or final BW. However, pigs previously fed increasing concentrations of Ca had improved (linear, P=0.003) G:F regardless of dietary STTD P content, resulting in no evidence for difference in overall growth performance across treatments. In conclusion, excess dietary Ca decreased ADG and G:F of nursery pigs especially in low STTD P diets. The STTD P levels estimated by NRC (2012) meet the requirement of 6 to 12 kg pigs when diets contain low Ca concentrations, but result in decreased ADG and G:F when diets contain more than 0.90% Ca.

	Treatment
STTD P:	NRC				>NRC			SEM
Ca, %:	0.65	0.90	1.20		0.65	0.90	1.20
d 0 to 24
ADG, g	230	226	195		236	226	224	8.1
G:F, g/kg	760	725	639		761	753	738	16.3