Meeting the estimated daily optimal standardized ileal digestible lysine-to-net energy ratios for first and second parity lactating sows improved piglet growth rates

One hundred three sows (52 first parity and 51 second parity) were used to evaluate the effect of meeting estimated daily optimal standardized ileal digestible (<b>SID</b>) Lys-to-net energy (<b>NE</b>) ratios throughout a 21-day lactation on piglet growth performance and sow body mobilization. A 2 × 2 factorial experimental design with the variables of parity and feeding program was used (n = 25 or 26). First and second parity sows were fed either a static feeding curve providing 3.9 g SID Lys/Mcal NE throughout the entirety of lactation (<b>CON</b>) or a dynamic feeding program that met estimated daily optimal SID Lys-to-NE ratios during lactation for maternal nitrogen retention (first parity sows; ranging from 5.48 to 4.95 g SID Lys/Mcal NE on days 1 and 20, respectively) or milk nitrogen output (second parity sows; ranging from 3.12 to 4.68 g SID Lys/Mcal NE on days 1 and 20, respectively; <b>PRE</b>). Weekly optimal SID Lys-to-NE ratios were determined for lactating primiparous and multiparous sows in previous studies, whereby only maternal nitrogen retention and only milk nitrogen output were influenced by SID Lys-to-NE ratio for primiparous and multiparous sows, respectively. Performance outcomes were not influenced by the interactive effect of feeding program and parity. Average daily feed intake did not differ between the CON and PRE feeding program, while second parity sows consumed more feed than first parity sows (Parity; <i>P</i> < 0.05). No differences were observed for maternal BW loss between the CON and PRE feeding programs, while second parity sows lost less BW than first parity sows (Parity; <i>P</i> < 0.05). Sows on the PRE feeding program tended to lose less backfat depth (<b>BF</b>) than sows on the CON program, regardless of parity (Feeding program; <i>P</i> = 0.094) and second parity sows lost less BF than first parity sows, regardless of feeding program (Parity; <i>P</i> < 0.05). Overall piglet average daily gain (<b>ADG</b>; 256 vs 246 ± 6 g) and piglet BW at weaning (6.45 vs 6.19 ± 0.17 kg) were greater for sows that received the PRE compared to the CON feeding program, regardless of parity (Feeding program; <i>P</i> < 0.05), with second parity sows having greater piglet BW and ADG than first parity sows, regardless of feeding program (Parity; <i>P</i> < 0.05). Therefore, providing a dynamic feeding program to meet estimated daily optimal SID Lys-to-NE ratios during lactation improved piglet growth performance without increasing maternal body weight losses in first and second parity sows.