Fuente: "milk OR dairy products" Anim Nutr. 2026 Jun 3;26:403-415. doi: 10.1016/j.aninu.2025.11.015. eCollection 2026 Sep.ABSTRACTThe potential changes in limiting amino acid (AA) requirements for lactating sows fed low-protein (LP) diets and the underlying physiological mechanisms remain unclear. This study evaluated the productive and physiological responses of lactating sows to LP diets, focusing on the optimal standardized ileal digestible lysine (SID Lys) supply. A total of 84 Landrace × Large White sows with similar parity (4.06 ± 0.16), expected farrowing dates and body weight (BW; 260.65 ± 1.25 kg) were randomly assigned to 6 groups with 14 replicates in each group and 1 sow per replicate. The control diet (CON) contained 18% crude protein (CP) and 0.78% SID Lys. Five LP diets contained 15% CP and similar net energy (NE) levels, with SID Lys levels of 0.66%, 0.72%, 0.78%, 0.84%, and 0.90%, respectively, achieved by adjusting the corn-to-soybean meal ratio and crystalline amino acids (CAAs) supplementation. The trial lasted for 28 d (from d 107 of gestation to d 21 postpartum). Compared with CON, 0.78% SID Lys-LP diet increased milk immunoglobulin M content (t-test, P = 0.002), improved apparent CP digestibility, and reduced serum urea nitrogen (SUN) content at d 14 and 21 of lactation, and also reduced milk urea nitrogen concentrations (t-test, P < 0.05). However, dietary CP reduction significantly decreased serum insulin-like growth factor-1 (IGF-1) levels and the digestibility of dietary crude fiber (t-test, P < 0.05). When the dietary SID Lys level in LP diets was further decreased to 0.66%, both sow and piglet production performance significantly declined (P < 0.05). However, increasing SID Lys to 0.84% in LP diets improved piglet performance, and the overall performance of both sows and piglets was not significantly different from that of CON, with the 0.84% SID Lys-LP group demonstrating better apparent utilization of dietary nitrogen and AA compared to all other groups (P > 0.05). A nonlinear fitting of sensitive indicators with linear and quadratic effects was conducted to estimate optimal SID Lys requirements for lactating sow. Breakpoints for 14 d SUN, maximizing piglet benefits (weaning litter weight and individual weight), and sow BW loss were 0.80%, 0.81%, and 0.85% using the broken-line linear model, and 0.86%, 0.90%, and 0.90% using the broken-line quadratic model. In conclusion, the LP diet containing 0.78% SID Lys did not adversely affect sow performance but affected piglet growth performance. Reducing dietary SID Lys in LP diets impaired the growth and development of 21 d suckling piglets, whereas increasing SID Lys and supplementing CAAs (Met, Thr, Trp, and Val) restored performance and mitigates adverse effects. The broken-line linear and quadratic models suggest the optimal range of SID Lys in LP diets for sows is between 0.80% and 0.90%.PMID:42433327 | PMC:PMC13351884 | DOI:10.1016/j.aninu.2025.11.015