178 A systematic review and meta-analysis of Ca digestibility and utilisation in growing and finishing pigs

Abstract The development of dietary recommendations based on digestible Ca values is an essential step to optimize pig performance and feed conversion because the present guidelines, expressed on total dietary Ca, are inadequate, as they ignore endogenous losses and the digestion process. A systematic review and meta-analysis of digestibility trials were performed to quantify factors affecting Ca absorption and retention, and to estimate endogenous Ca losses. Forty studies, corresponding to 201 dietary treatments performed on 1,204 growing pigs, were selected. Data analysis was performed in R using weighted linear mixed effects regression. The results indicated that while Ca absorption and retention (g/kg of BW/day) increased with increasing Ca (P < 0.001), with non-phytate-P (P < 0.001) and with exogenous phytase intakes (P < 0.001), these responses decreased with increasing phytate-P intake (P < 0.05). Interactions were detected between exogenous phytase and Ca intake (P < 0.001), indicating reduced efficacy of this enzyme, and between phytate-P intake and exogenous phytase (P < 0.05), indicating reversing of the direct negative effect of phytate-P on Ca absorption and retention. Based on the recommended Ca and P intake for a 25 kg pig, an exogenous phytase supplementation of 1,000 FTU/day could potentially improve Ca digestibility by 20–25%. There were no effects of animal characteristics (e.g. ‘genotype’) on Ca absorption and retention. The large amount of variance explained in Ca absorption (90%) and retention (91%) supported our a priori choice of independent variables. Estimated endogenous Ca losses were 239 mg/kg of DM (95% CI 114, 364). When scaled by bodyweight, the endogenous Ca excretion on Ca-and-P-free diets was 20.5 mg/kg of BW/day (95% CI 5.46, 36.5). These outcomes should contribute to a reassessment of Ca requirements, which should lead to a more accurate formulation of pig diets.