Effects of dietary calcium and phosphorus on reproductive performance and markers of bone turnover in stall- or group-housed sows

Increasing productivity and new housing standards necessitate a reevaluation of nutrient requirements for sows, including minerals. The objective of this study was to determine if the recommended levels of dietary Ca and P are adequate for sows housed in groups and that, therefore, have the potential for increased mobility. A total of 180 multiparous sows and gilts were assigned to 1 of 6 treatments. Treatments, arranged as a 3 x 2 factorial, included the main effects of dietary Ca: P-0.70: 0.55% Ca: P (as-fed basis; control), 0.60: 0.47% Ca: P (as-fed basis; Low CaP), and 0.81: 0.63% Ca: P (as-fed basis; High CaP)-and housing-stalls or groups. The trial was initiated when sows were moved from the breeding stalls to the gestation room at wk 4 or 5 after breeding. Sows were initially fed 2.3 kg/d. This allotment was increased to 3.0 kg/d 2 wk prior to farrowing. Group-housed sows, fed in individual stalls, were allowed access to a loafing area after feeding. Serum samples were collected at the start of the trial and on d 100 of gestation, and both serum and milk samples were collected at mid lactation and prior to weaning. Neither diet nor housing had an effect on the total number of piglets born, ADG from birth to weaning, or weaning weight (P > 0.10). The number of live-born piglets and birth weight were unaffected by diet (P > 0.10) but were improved by group housing relative to stalls (P < 0.05). In late gestation, group-housed sows fed the Low CaP diet had reduced serum Ca (diet x housing interaction, P = 0.02), and the greatest reduction (between d 28 and 100 of gestation) in serum P level was observed in group-housed sows fed the Low CaP diet (diet x housing interaction, P = 0.04). Osteocalcin and pyridinoline, markers of bone formation and resorption, respectively, were unaffected by diet or housing (P > 0.10). Results from these studies imply that the level of dietary Ca and P recommended by the NRC is adequate for sows of modern genetics, whether housed in stalls or groups.