| Fifteen Piglets of five group ,each group of three pigs at 1, 14, 28, 42 and 56 days of age were firstly used to study developmental mRNA expression of antibacterial peptide PR-39 by means of RT-PCR. The primers for PR-39 and p-actin were designed respectively according to the known porcine antibacterial peptide PR-39 gene and housekeeping gene p-actin sequence, the suitable MgCl2 concentration, cycles and the competetion between the two pairs of primers in PCR system were discussed. The results indicated that the MgCl2 concentration and cycle number were 2.5 mmol/L and 29, respectively. Furthermore, because of competetion between specific primers of PR-39 and P-actin, PCRs were conducted separately. An optimized RT-PCR was constructed to detect expression of PR-39 mRNA in piglets.The results showed that relative mRNA expression of PR-39 to p-actin (PR-39/P-actin ratio) was 0.45 in newborn, 0.74 in 14 days, 0.88 in 28 days, 0.22 in 42 days and went up to 2.30 in 56 days.Total ninety-six weanling pigs of 36 days of age were secondly devided into four groups at random on breed, sex and weight. Each of which includes three replicates of 8 weanling pigs, the control group received the basal diet (DE 3.17 MJ/kg, CP 18.5%), treatment 2, 3, 4 received the basal diet supplemented with 100 mg/kg, 3000 mg/kg, 100 mg/kg Zn as ZnO, ZnSO4 and Nano-ZnO, respectively. The piglets were fed experiment diet for 15 days after pretesting for 7days, weanling pigs were given adequate diets and free access to water. After feeding trial, pigs in each treatment were weighted, three pigs in each treatment were slaughtered, bone marrow tissue of left leg was collected, total RNA was extracted from bone marrow cells and wasreverse-transcribed to cDNA and stored in frozen state. RT-PCR constructed previously was adjusted to detect PR-39/p-actin ratio of mRNA expression.The results of feeding trial showed that supplementation of 3000 mg/kg Zn as ZnO increased ADG by 36.45% (P=0.01), as compared with control. Supplementation of 100 mg/kg Zn as ZnSO4 and Nano-ZnO increased ADG by 10.62(P=0.06) and 21.42%(P=0.05), respectively. Supplementation of 3000 mg/kg Zn as ZnO decreased F/G ratio by 25.74% (P<0.01), Supplementation of 100 mg/kg Zn as ZnSO4 and Nano-ZnO decreased F/G ratio by 18.57% (P=0.03) and 22.79% (P<0.05), respectively.The results of mRNA quantitation experiments showed that supplementation of 100 mg/kg ZnSO4 increased ratio of PR-39/0-actin by 38.4%, as compared with control. Consumption of 3000 mg/kg Zn as ZnO and 100 mg/kg Zn as Nano-ZnO increased it by 378.26%(P<0.01), 23.91%, respectively.Implication:(1) mRNA expression of antibacterial peptide PR-39 gene increased gradually with ages in suckling pigs, but it decreased in P<0st weaned pigs significantly. It indicates that weanning has great effect on PR-39 mRNA expression, down-regulation of PR-39 mRNA expression may be in intensive relation with immunity depression, high rate of diarrhera and death in weanling pigs.(2) Supplementation of different form of chemical Zinc all enhanced mRNA expression of PR-39 gene, of which supplementation of 3000 mg/kg Zn as ZnO was the best. This indicates that Zinc element participates the regulation of PR-39 mRNA expression, and this may partially explain how supplementation of high level Zinc can effectively prevent and control diarrhrea, improve immunity in piglets.
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