Nitrogen and trace mineral balance of pregnant gilts under low dietary zinc intake.

Nitrogen (N) and mineral balance studies were carried out in littermate pregnant gilts fed either a zinc (Zn)-deficient basal diet (10 mg/Kg Zn) or a Zn-supplemented diet (50 mg/kg) from day 22 of pregnancy and in open gilts fed the Zn-supplemented diet. Collections were carried out at 60-66 and at 100-106 days of pregnancy. Open controls had N retention similar to that of Zn-restricted and Zn-supplemented gilts in early pregnancy. A trend towards better N utilization due to Zn supplementation was observed in late pregnancy. Pregnant, Zn-supplemented gilts were in negative Zn and copper (Cu) balance in early pregnancy, whereas open controls and Zn-restricted pregnant gilts were in positive Zn and Cu balance. Utilization of Zn and Cu tended to improve in late pregnancy with Zn-restricted gilts retaining somewhat more Zn and Cu than controls. In early pregnancy, Zn-supplemented gilts retained proportions of dietary iron (Fe) similar to that of open controls and twice the proportion retained by Zn-restricted gilts; the latter tended to increase Fe retention in late pregnancy, but Fe retentions by control gilts were still higher. Pregnant gilts were in negative manganese (Mn) balance in early pregnancy whereas open gilts were in positive balance. In late pregnancy both groups tended to improve their Mn economy, being close to Mn equilibrium. Positive Zn balance in Zn-restricted gilts was achieved by marked reduction of fecal Zn. The Zn-saving mechanisms appeared to influence Cu and Fe retention.