Effect of nitrogen supply on the retention and excretion of nitrogen and on energy metabolism of pregnant sows

To reduce nitrogen excretion (NEx) the effect of nitrogen supply on nitrogen retention (NR) and NEx was studied in pregnant sows during three parities. A nitrogen supply of 40 g/day (treatment L) was compared with 62 g/day (treatment C) during day 0 to 85 of pregnancy. In the last month of pregnancy nitrogen supply on treatment L was 50 g/day and on treatment C 74 g/day. Faecal digestible lysine supply followed the same pattern as nitrogen. Nitrogen and energy balances were measured during mid pregnancy (day 50 to 60; no. = 22) and late pregnancy (day 105 to 112; no. = 60). During mid pregnancy treatments had a minor affect on NR and energy metabolism. NEx on treatment L was proportionately about 0·40 lower than on treatment C. During late pregnancy NR was lower on treatment L than on treatment C. NEx on treatment L was proportionately reduced by 0·35 compared with treatment C. In parity 1 the lower NR on treatment L was compensated by a higher fat gain. Results indicate that nitrogen and faecal digestible lysine supply on treatment L were close to minimal requirement in late pregnancy. Assumed values for maintenance requirement of nitrogen (0·45 g N per kg M 0·75 ) and efficiency of ingested nitrogen to NR (0·6) were in line with the results of the balance trials. The observed nitrogen retention of sows, especially during mid pregnancy, permits a reduced nitrogen supply to reduce NEx.