Effect of dietary phosphorus and calcium depletion-repletion on pig performance and bone quality

Feeding strategies such as P and Ca depletion and repletion have been proposed to reduce the use of phosphate or improve P utilisation efficiency in pig diets, thereby contributing to the sustainability of the sector. A total of 48 entire male pigs (18.47 ± 3.18 kg BW) were fed a control diet (C = 100% of requirements) and a restricted diet (R = 80-90% of digestive requirements of P and Ca, respectively) in three growth phases, with the following feeding strategies: CCC, RCC, RRC and RRR. At each phase, growth performance and bone characteristics (proportion of low-, medium-, high- and very high-density bones, and total density) of live animals were analysed, as well as carcasses and individual bones, using computed tomography equipment. Additionally, carcass and meat quality were evaluated at slaughter. Although there were differences in some phases, the overall analysis showed that P and Ca depletion-repletion did not affect the animals' growth. Reducing dietary Ca and P caused an increase in the proportion of low-density bones, a decrease in the proportion of medium- and high-density bones, and a decrease in total bone density in depleted pigs compared with control animals at each phase. At the end of phase 2, bone characteristics of RC pigs tended to follow a similar pattern observed in RR pigs when compared with CC animals. However, at the end of phase 3, RCC and RRC pigs exhibited similar bone characteristics than CCC animals, due to the recovery in bone mineralisation. Additionally, body characteristics measured on tomograms of the repleted animals showed a quadratic effect, where RCC pigs exhibited a decrease in total body area, central subcutaneous fat thickness, and loin eye area in some body regions, demonstrating that P and Ca depletion-repletion affected the anatomical regions in different ways. On the other hand, carcass, head, 1st rib, and 4th last rib bone characteristics were affected by the R diet, where the RRR strategy showed significantly lower density than the CCC strategy. In the conditions of this study, the application of P and Ca depletion-repletion strategies, or full depletion (RRR), could be an alternative to reduce the use of phosphate in pig diets without impacting performances and bone characteristics.