Abstract: The purpose of this study was to investigate the growth promoting effect and the safety of the vaccine in crossbred buffalo growing cattle immunized with somatostatin and corticostatin co-expression DNA vaccine.The identified plasmid of pVGS/2SS-2A-S/CST-asd was electroporated into attenuated Salmonella Choleraesuis C500 to construct the co-expression live vector vaccine of somatostatin and corticostatin.Sixteen 6-12 months old crossbred buffalo growing cattle were randomly divided into low dosages group (TL),middle dosages group (TM),high dosages group(TH) and negative control group(NC).At the initial immunization,immunization was performed at 09:00 and 15:00 twice a day for 3 d,and the same procedure was used to strengthen immunization once after 2 weeks.The experimental group and control group was immunized with co-expression vaccine and PBS respectively,and the effect of daily weight gain and immune response level in different periods after the primary immunization.The immune response results showed that all dose groups induced immune response after the primary immunization,the antibody of somatostatin (SS) in TL group was higher than that in TM and TH groups at 2 weeks after primary immunization,and the positive rate of SS antibody in TM group was the highest,which was 100% and better than that in TL (75%) and TH groups (50%).However,the antibody of cortistatin(CST) after 2 weeks of primary immunization showed a completely opposite trend,high dosages group showed the best performance,and with the decrease of immune dose,the antibody of CST also showed a downward trend.After 7 weeks of primary immunization,antibody of SS and CST and positive rate showed a downward trend,but some buffaloes showed an upward trend.In the aspect of cytokines,it was found that the interleukin 4 (IL-4) level at 2 weeks after the primary immunizationin TL and TM groups was significantly higher than that in control group (P<0.01).At 7 weeks after primary immunization,the IL-4 level in control group was significantly higher than that in TL group (P<0.05),and there was no significant difference with other groups (P>0.05).The level of immune interferon γ (INF-γ) at 2 weeks after the primary immunization in control group was significantly higher than that in TL and TM groups (P<0.05).The INF-γ level at 7 weeks after the primary immunizationin in control group was significantly higher than that in TL group (P<0.05),but there was no significant difference with other groups (P>0.05).The IL-4 level at 2 weeks after the primary immunizationin in antibody positive group was significantly higher than that in negative group (P<0.01),and was significantly lower than that in control group at 7 weeks after the primaryimmunization (P<0.05),but the INF-γ level at 2 and 7 weeks after the primary immunizationinin in the antibody positive group was significantly lower than that in the negative group (P<0.05).The weight gain effect test showed that the average daily gain of each experimental group was significantly higher than that of control group at 2 weeks after the primary immunization (P<0.05),but there was no significant difference among the groups in other periods (P>0.05).The antibody positive group was also significantly higher than the negative group at 2 weeks after the primary immunization (P<0.05).The hormone test results showed that growth hormone (GH) and insulin-like growth factor 1 (IGF-1) levels in the experimental groups were significantly higher than those in control group at 2 weeks after the primary immunization (P<0.01),while the levels of GH and IGF-1 in the low dosages group were significantly lower than those in control group (P<0.05),but there was no significant difference between the other groups (P>0.05),the levels of GH and IGF-1 in the antibody positive group were significantly higher than those in the negative group at 2 weeks after the primary immunization (P<0.01),and were significantly lower than those in control group at 7 weeks after the primary immunization (P<0.01).In the aspect of safety,no target fragment was detected in water,soil and fecal samples collected in each period.The results showed that the co-expression vaccine could induce immune response and promote the average daily gain of growing cattle,and no safety problem was detected.

Key words: somatostatin; cortistatin; DNA vaccine; crossbred buffalo; growing cattle