EFFECT OF NITROGEN SUPPLY ON NITROGEN AND ENERGY-METABOLISM IN LACTATING SOWS

In 56 balance trials sows received diets in pregnancy containing (g/kg diet) either 24.7 nitrogen (N) (C) or 16.7 N (L) followed by diets in lactation containing (g/kg dietary dry matter) either 28.5 N and 8.4 lysine (C) or 32.8 N and 10.3 lysine (H). N and energy balance during lactation (day 4 to 25) were made during three successive parities (23 , 17 and 16 sows in parities 1, 2 and 3, respectively). Retention in p iglets was calculated from their body composition at weaning. Mean dai ly litter gain was 2.72 kg/day and was not affected by the dietary tre atments. Mean body-weight loss of sows tons 0.67 kg/day and was lower only in parity 2 on lactation treatment H compared with lactation trea tment C. N retention was less negative on lactation treatment H than o n lactation treatment C (significant in parity 2) and N retention was less negative on pregnancy treatment L than on pregnancy treatment C ( significant in parity 3). Fat mobilization on lactation treatment H wa s higher than on lactation treatment C (significant in parties 2 and 3 ). The proportion of energy mobilized as protein to the total energy m obilization tons significantly lower on lactation treatment H compared with lactation treatment C. Estimated daily N, lysine and ileal diges tible lysine requirements for first parity lactating sows were 162 g, 48 g and 37 g respectively. For second parity sows 179 g, 54 g and 42 g and for third parity sows, 185g, 56g and 43 g. N excretion during la ctation teas proportionately about 0.6 of ingested N. This resulted in an N excretion of about 23 kg N during a 25-day lactation period. Aft er correction for differences in litter size, body weight of sows, dai ly litter gain and N mobilization increased with parity number.