Effects of the Reproductive Cycle and Age on Calcium and Phosphorus Metabolism and Bone Integrity of Sows

The purpose of this study was to determine the effects of stage of the reproductive cycle and age on Ca and P metabolism and bone integrity of sows. Five-day balance studies were conducted with first- and fifth-parity sows, and sows were slaughtered during the last trimester of gestation, at the end of lactation, or during the last trimester of the subsequent gestation. First-parity sows were studied during their first gestation (n = 11), first lactation (n = 10), or second gestation (n = 10). Fifth-parity sows were examined during their fifth gestation (n = 10), fifth lactation (n = 9), or sixth gestation (n = 9). All sows were fed 1.9 kg/d of a common diet (.76% Ca and .63% P) during gestation and were allowed ad libitum access to the same diet during lactation. Digestibilities of Ca and P were much greater during lactation than during gestation. During gestation, young sows absorbed and retained more Ca and P than did mature sows. However, during lactation, mature sows consumed more feed, and therefore Ca and P, and retained more Ca and P than did young sows. Bones of mature sows were larger, more mineralized, and stronger than the bones of young sows. Bone weight and strength decreased during lactation and increased during the subsequent gestation. Changes in weight and strength were greater in young sows than in mature sows.