Impact of reduced dietary calcium and phosphorus levels on nutrient digestibility, metabolic homeostasis, and immune responses in weaned piglets

This study investigated the effects of dietary calcium (Ca) and phosphorus (P) levels on growth performance, diarrhea incidence, blood parameters, serum biochemical indices, nutrient digestibility, and antioxidant and immune functions in weaned piglets. A total of 120 healthy piglets (initial body weight: 7.99 ± 1.15 kg) were randomly allocated to two treatment groups: a high Ca–P diet (HCP: Ca 0.85%, P 0.70%) and a low Ca–P diet (LCP: Ca 0.60%, P 0.60%). Each treatment had six replicates with ten piglets per replicate, and the experimental period lasted 39 days. Compared with the high Ca–P group, the low Ca–P group showed partially increased average daily gain (ADG) and average daily feed intake (ADFI) and a reduced feed-to-gain ratio (F/G), but the differences were not significant ( P > 0.05). No significant difference in diarrhea incidence was observed between the two groups ( P > 0.05). The apparent digestibility of crude protein, crude fiber, crude ash, calcium, and total phosphorus in the low Ca–P group was significantly higher than that in the high Ca–P group ( P < 0.05). Compared with the high Ca–P group, serum aspartate aminotransferase (AST) activity in the low Ca–P group was reduced by 48.16% ( P < 0.05), while white blood cell and monocyte counts and serum interleukin-10 (IL-10) and interferon-γ (IFN-γ) concentrations were significantly decreased ( P < 0.05); in contrast, serum alkaline phosphatase (ALP) activity increased by 27.45% ( P < 0.05). In summary, reducing dietary Ca and P levels to 0.60% improved nutrient digestibility, alleviated hepatic metabolic stress, and reduced basal immune activation in weaned piglets. These results provide useful insights for optimizing dietary mineral supply during the early weaning period. A primary limitation of this study is that only two Ca-P levels were tested, and bone traits, and long-term performance were not evaluated.