Abstract: [Objective] This study was conducted to explore the effects of dietary supplementation of plant essential oils prepared with different processes on growth performance, intestinal digestive enzyme activity and serum immunoglobulin level of weaned piglets.[Method]A total of 198 heads of 21-day-old Duroc × Landrace × Yorkshire （DLY） healthy weaned piglets with an average weight of （5.687±0.761） kg were randomly assigned into 3 groups, with 11 replicates in each group and 6 piglets in each replicate. The control group fed a basal diet. The two experimental groups fed the same basal diet in which 300 g/t of a micro-encapsulated and control-released plant essential oil （MECR-PEO） or a mixed plant essential oil （M-PEO） were supplemented, respectively. The feeding experiment lasted for 21 days. The average daily feed intake, average daily weight gain and feed to weight gain ratio of the experimental piglets at 22-28 days, 29-35 days and 36-42 days of age, as well as the diarrhea rate at 22-42 days of age were calculated. On the 21^st day of the feeding experiment, the duodenal chyme was collected, and the activities of intestinal trypsin, amylase and lipase were measured. At the end of the feeding experiment, blood samples were collected with serum prepared. ELISA assay was used to detect the serum levels of IgG, IgM and IgA. [Result] At 22-28 days and 29-35 days of age, the dietary supplementation of the two types of plant essential oils had the trends of increasing the average daily weight gain and average daily feed intake, as well as reducing the feed to weight gain ratio （P>0.05） compared with the control group. At 36-42 days of age, the piglets received the dietary supplementation of MECR-PEO had significantly （P<0.05） higher average daily weight gain and significantly （P<0.05） lower feed to weight gain ratio than those in the control group; the piglets received the dietary supplementation of M-PEO had higher average daily weight gain and average daily feed intake （P>0.05）, as well as lower feed to weight gain ratio than those in the control group （P>0.05）. At 22-42 days of age, the diarrhea rates of the piglets in both plant essential oil supplementation groups were significantly （P<0.05） reduced compared with the control group. The MECR-PEO supplementation group exhibited a better performance, with a decrease in diarrhea rate of 67.79% compared to the control group. Piglets in the MECR-PEO supplementation group had significantly （P<0.05） higher activities of duodenal trypsin, amylase and lipase in comparison to those in the control group, and had significantly （P<0.05） higher lipase activity in comparison to those in the M-PEO supplementation group. Significantly （P<0.05） higher duodenal trypsin activity was observed in the M-PEO supplementation group compared to the control group. Significantly （P<0.05） elevated serum levels of IgG and IgM in the MECR-PEO supplementation group was found compared with the control group, and significantly （P<0.05） elevated serum IgM level in the M-PEO supplementation group was found compared with the control group. [Conclusion] Dietary supplementation of MECR-PEO and M-PEO had positive effects on improving growth performance as well as enhancing intestinal digestive enzyme activity and serum immunoglobulin level in weaned piglets. The effects of MECR-PEO were better.

Key words: micro-encapsulated and control-released plant essential oil, mixed plant essential oil, weaned piglet, growth performance