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 piglets was calculated from their body composition at weaning.

Mean daily litter gain was 2·72 kg/day and was not affected by the dietary treatments. Mean body-weight loss of sows was 0·67 kg/day and was lower only in parity 2 on lactation treatment H compared with lactation treatment C. N retention was less negative on lactation treatment H than on lactation treatment C (significant in parity 1) 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 was higher than on lactation treatment C (significant in parities 2 and 3). The proportion of energy mobilized as protein to the total energy mobilization was significantly lower on lactation treatment H compared with lactation treatment C. Estimated daily N, lysine and Heal digestible 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 185 g, 56 g and 43 g. N excretion during lactation was proportionately about 0·6 of ingested N. This resulted in an N excretion of about 2·3 kg N during a 25-day lactation period. After correction for differences in litter size, body weight of sows, daily litter gain and N mobilization increased with parity number.