Effects of dietary Ca and digestible P concentrations and addition of phytase on growth performance of nursery pigs

Appropriate dietary calcium (Ca) and phosphorous (P) concentrations are essential for nursery pig performance. The total Ca and digestible P requirements estimated by NRC (2012) are 0.83 and 0.45%, respectively, for 6 kg pigs. Research has shown that feeding excess dietary Ca impairs P digestibility, therefore reducing growth performance and bone development in nursery pigs (González-Vega et al. 2016). The objective of this study was to evaluate growth performance and bone ash concentration of nursery pigs in response to combinations of dietary Ca and P levels provided by inorganic sources or phytase (1000 FTU of Ronozyme HiPhos 2500; DSM Nutritional Products Inc., Parsippany, NJ, USA).

A total of 720 pigs (PIC 1050 × 280, initially 6.1 ± 0.23 kg) were used in a 42-day growth study. Pens of pigs (10 pigs/pen, 12 pens/treatment) were blocked by initial pen weight, and within blocks, pens were allotted randomly to one of six treatments. Dietary treatments were arranged in a 2 × 3 factorial with two levels of Ca (0.58 v. 1.03%) and three standardised total tract digestible (STTD) P treatments (0.33 and 0.45% without phytase, and 0.45% with 0.12% of the P being released by phytase). Diets were provided in three phases with pigs fed experimental diets in Phase 1 (d 0 to 14) and Phase 2 (d 14 to 28), followed by a common Phase 3 diet from d 28 to 42. Average daily gain (ADG), feed intake (ADFI), and feed efficiency (G : F) were determined every 7 days. Data were analysed using the Proc GLIMMIX of SAS (v9.4, SAS Institute Inc., Cary, NC, USA).

For the majority of the feeding periods, Ca × P interactions were observed for growth responses (P < 0.05). From d 0 to 28 (Table 1), when diets contained a low Ca concentration, pigs fed 0.45% STTD P with phytase had greater (P < 0.01) ADG and ADFI compared with those fed 0.45% STTD P without phytase, and pigs fed 0.33% STTD P. When high Ca was fed, ADG and ADFI were similar among pigs fed 0.45% STTD P with or without phytase, but were greater than those fed 0.33% STTD P. Feed efficiency was reduced (P < 0.01) when low STTD P and high Ca were added to diet, compared with other dietary treatments. During Phase 3, pigs previously fed 0.33% STTD P had similar ADG, but decreased (P < 0.05) ADFI and improved G : F compared with pigs previously fed 0.45% STTD P with or without phytase. However, pigs fed 0.33% STTD P with high Ca were not able to fully compensate the negative effects of P deficiency resulting in decreased (P < 0.05) overall ADG and ADFI compared with pigs fed 0.45% STTD P diet with or without phytase. On d 21, one median-weight gilt from each pen was killed and fibulas were collected for analysis of bone ash content. Pigs fed 0.33% STTD P had decreased (P < 0.05) bone ash concentration compared with those fed 0.45% STTD P with or without phytase when high Ca was added to diets, but this P effect was not observed when diets contained low Ca (Ca × P interaction, P = 0.007).

Table 1.  Effects of Ca and P concentrations on growth performance of nursery pigs from d 0 to 28

In conclusion, excess Ca in diets decreased nursery pig performance and bone ash content only when diets were deficient in STTD P. Adding phytase to achieve 0.45% STTD P improved ADG and ADFI of pigs compared with diets containing 0.45% STTD P without phytase, indicating a potential underestimation of the P release from phytase or an increased availability of other nutrients liberated by phytase.