| The effects of antibiotics on growth-promoting of young animals were obvious. It is a crucial period for animals to produce and establish their immune system in the early stage. Antibiotics in diets depress the pathogenic microorganisms, but also kill the beneficial microorganisms, which disturb the body's micro-ecological balance. In view of animal products safety, withdrawal of antibiotics in diets is required. To our knowledge, the relationships between effect of enramycin (ER) on promoting growth and regulating immune functions during the periods of withdrawal and stress have not been reported. Therefore, the aim of this study was to investigate effects of normal and over dosage of ER on the performance, immune functions of weaned piglets.Experiment 1 Effects of ER on growth performance and serum biochemical indexes of weaned pigletsIn this experiment, the effects of normal and over dosage of ER on the performance and blood biochemical indexes of early-weaned piglets were investigated during the periods with or without the additive. A total of 36 Duroc×Landrace×Yorksire (DLY) piglets weaned at 21d were randomly assigned to 1 of 3 dietary groups of 12 pigs each on the basis of body weight. The three dietary treatments were 1) a basal diet (control) containing no ER,2) basal+5mg/kg ER, and 3) basal+80mg/kg ER. The total 28-day trial was divided into 2 phages:ER-supplemented period (ER time) of 3 weeks (phage 1), and withdrawal time of one week (phage 2). In the morning of d 22 and d 29, piglets were weighted and fasting blood samples were collected to prepare the serum.Results showed that 5 mg/kg and 80 mg/kg ER dietary treatments resulted in the improvements of average daily gain and feed intake in various degrees during different stages (d 0-7, d 8-14, d 15-21, and d 0-21), but had no effects on feed conversion. During withdrawal time (d 22-28), the performance of early-weaned piglets fed ER diets was slightly better than the piglets fed the control diet. ER in diets increased serum nitric oxide concentration of early-weaned piglets in some cases, but had no effects on urea nitrogen and MDA.Over dosage of ER in diet increased serum LDH activity of weaned piglets in some cases.The present study indicates that enramycin supplementation in diet may improve piglets performance, and has no significant negative effects on metabolism.Experiment 2 Eeffects of ER on growth performance and serum biochemical indexes of LPS-challenged weaned pigletsIn this experiment, blood biochemical parameters and growth performance of LPS-challenged weaned piglets were investigated by testing the blood biochemical parameters and growth factor involved in.The experiment was conducted by 2×3 factorial design that involved immune challenge (intraperitoneal injection of LPS or saline) and three ER levels (0,5 and 80 mg/kg). At the beginning of LPS-challenged period (d 29), after fasting and weighing, piglets of each treatment in experiment 1 were divided into two groups on the basis of body weight and were injected intraperitoneally with LPS (serological type 055:B5, Sigma, USA) at a dosage of 200μg/kg body weight or equivalent saline as a control. Blood samples after fasting were collected before and 2.5 h,3 d after stress.Results showed that on d 3 after stress, average daily gain and average daily feed intake of the piglets challenged with LPS decreased significantly (P<0.05). A significant increase of average daily feed intake was observed in LPS-challenged pigs fed the ER diet (P< 0.05). In addition, there was a tendency toward remission the LPS-induced average daily feed intake decline by ER. After the withdrawal period, nitric oxide, urea nitrogen, MDA, lactate dehydrogenase, cortisol and insulin-like growth factor 1 concentrations in the serum were not significantly affected by ER (P> 0.05). Two and a half hours after LPS injection, MDA, cortisol and insulin-like growth factor 1 levels in serum increased significantly (P<0.05). Three days after LPS injection, serum insulin-like growth factor 1 concentration was significantly increased (P<0.05), serum nitric oxide concentration was significantly decreased (P <0.05), and there was a tendency toward elevated serum cortisol concentration (P <0.1), while ER significantly reduced the serum insulin-like growth factor 1 concentrations (P< 0.05). In addition, a significant interaction effect of ER and LPS on serum insulin-like growth factor 1 regulation (P<0.05) was observed, namely, ER played remission role of LPS-induced serum insulin-like growth factor 1 concentration increase.In conclusion, intraperitoneal injection of LPS significantly affects the growth performance of piglets and serum nitric oxide, malondialdehyde, cortisol, insulin-like growth factor 1 levels, and diets supplemented with ER could alleviate the negative effects of LPS in some extent.Experiment 3 Effects of ER on the immune function of LPS-challenged pigletsEffects of normal and over dosage of ER on immune function of the LPS-challenged piglets were investigated in this experiment. The experimental design was the same as described in experiment 2. Fasting blood samples were collected before and 2.5 h,3 d after challenge. At the end of the trial, all piglets were slaughtered and the kidney, spleen, thymus, lung, inguinal lymph nodes, mesenteric lymph nodes and liver were taken. The concentrations of serum cytokines, blood lymphocyte subsets and serum immunoglobulins, and P-defensins and Toll-like receptor gene expression levels in different tissues were detected.Results showed that, after the withdrawal period, there was no significant difference in the lymphocyte subsets, immunoglobulin and cytokine levels before LPS challenge (P>0.05). After LPS challenge, blood lymphocytes increased significantly, and the increase of CD8+cell subsets (P< 0.05) resulted in a significant decline of CD4+/CD8+ratio (P<0.05). Compared with the non-immune stress piglets, blood immunoglobulin (IgA, IgG and IgM) and cytokines (IL-1, IL-2, IL-6 and TNF-α) levels were significantly increased (P<0.05), and pBDl,2,3, and TLR3,4 gene expression levels in the thymus were significantly decreased (P<0.05), in piglets challenged with LPS. After the withdrawal period, there was no significant difference in immune parameters among each treatment before LPS injection. However, ER significantly affected blood IL-1 and IgA concentrations (P<0.05) of LPS-challenged piglets, and adjusted the gene expression of pBD1,2,3, and TLR3,4 in different organizations (especially in the thymus and spleen), and in which there were some interaction effects between ER and the immune stress caused by LPS.In conclusion, both the LPS-induced immune stress and dietary ER regulated the specific and innate immune responses of weaned piglets, and there were interaction effects to some extent. Diets supplemented with ER could alleviate the immunological stress induced by LPS.ImplicationsSupplementation of Enramycin in diets may improve the performance of early weaned piglets, also could alleviate the negative effects of immunological stress on metabolism and immune function of piglets.Neither further improvement nor significant negative effects of over dosage of ER on immune function of LPS-challenged piglets had been observed. It implicated that ER was safe for pigs at wide dose of dietary supplementation. |
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