Abstract: The purpose of this experiment was to study the effects of serine on growth performance, intestinal morphology and immune related indexes of lactating piglets with intrauterine growth retardation (IUGR). Sixteen healthy newborn piglets with similar body weight of (1.27±0.01) kg were selected as the control group, and 16 newborn IUGR piglets with similar body weight of (0.98±0.01) kg were selected as the treatment group. Eight IUGR piglets were fed 0.8% 3 mL serine at the 1st, 4th, 7th, 11th, 15th, 19th, 22nd and 26th day, and eight healthy piglets were fed 3 mL normal saline at the same time. All piglets were suckling normally. The test period was 28 days. Other piglets were slaughtered on the first day of newborn. The results showed that:1) Newborn IUGR piglets have significantly lower body weight than normal piglets (P<0.05), but after serine administration, there is no significant difference in body weight between piglets in two groups at 28 days (P>0.05); 2) On the first day of newborn, the villi in the jejunum and ileum of IUGR piglets were short and irregularly flocculent on the surface, with significant inflammation. After feeding with serine to the 28th day, the villi in the jejunum and ileum of IUGR piglets were tightly arranged and smooth on the surface, without significant inflammatory response, the villus height of the ileum in IUGR piglets significantly increased compared to the control group (P<0.05), but there was no significant improvement in the villus height and crypt depth of the jejunum in IUGR piglets compared to the control group (P>0.05); 3) On the first day, the serum albumin (ALB), immunoglobulin A (IgA), immunoglobulin G (IgG) and immunoglobulin M (IgM) content of IUGR piglets had no significant difference compared with those of the control group (P>0.05), the total protein (TP) content and aspartate aminotransferase (AST) activity were significantly lower than those of the control group (P<0.05), the alanine aminotransferase (ALT) activity was significantly higher (P<0.05), after feeding with serine to the 28th days, the serum ALB content of IUGR piglets was significantly higher than that of the control group (P<0.05), while the TP content, AST and ALT activities had no significant difference compared with the control group (P>0.05), however, serine could not make the content of IgA, IgG and IgM in serum of IUGR piglets reach the level of normal piglets at the 28th days; 4) On the first day, compared with the control group, the number of CD4⁺T cells in the peripheral blood of IUGR piglets showed a decreasing trend(P=0.077), the number of CD8⁺T cells significantly increased (P<0.05), and the ratio of CD4⁺to CD8⁺significantly decreased (P<0.05), after feeding with serine to the 28th days, there was no significant difference in the number of CD4⁺T cells and CD8⁺T cells in the peripheral blood of IUGR piglets compared to the control group(P>0.05). 5) After 28 days of serine administration, the protein expression of interleukin 10(IL-10) in jejunum significantly increased. In summary, exogenous addition of serine can promote the growth and development of IUGR newborn piglets, improve the morphology and structure of intestine, and improve the immune function of piglets, so that the body weight of IUGR piglets can reach the level of normal piglets, and the results may provide certain reference for the research and feeding of IUGR piglets, and provide new ideas for the nutritional regulation of IUGR piglets as well.

Key words: serine, intrauterine growth retardation, intestine, T cells, immunity