Lactational and subsequent reproductive responses of lactating sows to dietary lysine (protein) concentration

Gilts (n = 208) were used to evaluate the effect of lysine (protein) intake over three parities on lactation and subsequent reproductive performance. Sows were assigned randomly to one of five experimental diets at each farro wing. The five corn-soybean meal-based lactation diets contained increasing concentrations of total lysine (.60, .85, 1.10, 1.35, and 1.60%) and CP(14 .67, 18.15, 21.60, 25.26, and 28.82%). Other amino acids were provided at a minimum of 105% of the NRC (1988) ratio to the lysine requirement. Sows ha d ad libitum access to their assigned diets from parturition until weaning (19.5 +/- .2 d postpartum). All sows were fed a common gestation diet (14% CP and .68% lysine) from weaning to next farrowing. Litter size was standar dized by d 3 postpartum to 10 pigs in parity 1 and 11 pigs in parity 2 and 3. Increasing dietary lysine (protein) linearly decreased (P <.05) voluntar y feed intake of parity 1 (from 5.4 to 4.6 kg/d), 2 (from 6.5 to 5.8 kg/d), and 3 sows (from 6.8 to 6.2 kg/d). With the increase of dietary lysine (pr otein) concentration during lactation, litter weight gain responded quadrat ically (P <.05) in all three parities. Maximal litter ADG was 2.06, 2.36, a nd 2.49 kg/d in parities 1, 2, and 3, respectively, which occurred at about 44, 55, and 56 g/d of lysine intake for parity 1, 2, and 3 sows, respectiv ely. Increasing dietary lysine (protein) had no effect (P >.1) on sow weigh t change, weaning-to-estrus interval, and farrowing rate in all three parit ies and no effect on backfat change in parity 2 and 3, but tended to increa se backfat loss linearly (P <.1) in parity 1. A Linear decrease of second l itter size (total born, from 11.7 to 10.1, P <.1; born alive, from 11.0 to 8.9, P <.01) was observed when dietary lysine (protein) increased during th e first lactation. Lysine (protein) intake during the second lactation had a quadratic effect on third litter size (P <.05; total born: 13.3, 11.2, 11 .6, 11.9, and 13.6; born alive: 11.8, 10.1, 10.3, 11.2, and 12.4). However, fourth litter size was not influenced by lysine (protein) intake during th e third lactation. These results suggest that the lysine (protein) requirem ent for subsequent reproduction is not higher than that for milk production . Parity influences the lysine (protein) requirement for lactating sows and the response of subsequent litter size to previous lactation lysine (prote in) intake.