Objective  Effects of lysine content in diet on the reproductive performance, serum biochemistry, and excretion nitrogen of sows in late gestation stage were determined.

  Method  A total of 64 healthy, pregnant, crossbred sows (Large White×Landrace) with 3–7 parities and a similar parturition date was randomly divided into 4 groups. Each group consisting of 16 replicates and one reference sow were fed with forage containing a digestible lysine level at 0.58%, 0.63%, 0.68% or 0.73%. Feeding the experimental diet on the sows started at the 80^th day after artificial insemination and finished after farrowing.

  Result  The weight of newly born litters in the 0.63% lysine group was significantly higher than that in the 0.58% group by 8.26%, and that in the 0.73% group by 7.87% (P＜0.05). The piglets at birth weighed significantly higher in the 0.63% group than the 0.58% group by 5.84% (P＜0.05). In the 0.63% group, the serum urea nitrogen was significantly lower than either the 0.58%, 0.68% or 0.73% group; the insulin significantly higher than the 0.58% or the 0.73% group; the serum lysine and threonine significantly lower than the 0.58% or the 0.73% group; the leucine and isoleucine significantly lower than the 0.73% group; the crude protein digestibility significantly higher than the 0.73% group; and, the excretion nitrogen significantly lower than the 0.68% or the 0.73% group.

  Conclusion  When the sows were fed at late gestation stage with a diet that contained 0.63% digestible lysine, an improved reproductive performance in them could be expected.