Abstract: The aim of this study was to investigate the effects of excess lysine on weaned piglets in vivo and in vitro. A total of 144 weaned piglets (Duroc×Landrace×Yorkshire) were randomly divided into 4 groups, 6 replicates for each group, 6 piglets for each replicate (3 barrows and 3 sows). The pigs in different groups were fed with excessive standardized ileal digestibility lysine (SID Lys) of 1.3%, 2.6%, 3.9% and 5.2%, respectively in the diet to observe its effects on growth performance, visceral indexes and physiological and biochemical indicators. Using IPEC-J2 as an in vitro model, the proliferation of IPEC-J2 cells was measured by adding lysine and other amino acids according to the type and ratio of amino acids in the culture medium and nutritional requirements, and attempting to reduce the adverse effects of excessive addition of lysine by balancing other amino acids. The results showed that, with the increase of the amount of SID Lys in the diets, the growth performance of weaned piglets significantly decreased (P<0.05), the mean corpuscular hemoglobin (MCH), some serum free amino acids and intestinal morphology were affected. When lysine was 2.0 mmol·L^-1in culture medium, the viability of IPEC-J2 cells significantly decreased(P<0.05), with the original lysine concentration in the medium (0.5 mmol·L^-1) being the optimum concentration for IPEC-J2 growth. Cell viability was improved to some extent when other essential amino acids were supplemented according to the balanced ratio of amino acids in the medium; Cell viability varied with treatment time when the corresponding concentrations of arginine and histidine were supplemented according to the optimum ratio of porcine basic amino acids. The study demonstrated that the addition of excessive lysine has negative effect on the growth of weaned piglets. The balance of amino acids should be fully considered in practical applications.

Key words: lysine, weaned piglets, IPEC-J2