Effect of Antimicrobial Supplementation on Expression of Pept1, PepT2 and LEAP2 Transcripts in Gastrointestinal Tract of Broiler Chickens

Introduction:

 Unlike antibiotics, probiotic shows not only positive effects on microbiota in digestive tract but also helps in digestion process. Probiotic affects the commensal and pathogen bacterial balance in intestine and make changes in benefit of useful bacteria. On the other hand, the biological activity of herbal essential oils is discovered since many years ago. Herbal essential oils were suggested as the newest growth promoter replaced with traditional growth promoters such as antibiotics in animal production. It was showed that the use of probiotic can impact the expression of peptide carriers in the cytoplasmic membrane cells. On the cell membrane, the carrier proteins transfer the peptides as tri or di-peptides into the cell. The potential of carrier proteins in material transfer and other remedy activity attracted the attentions to use them as drug precursors. Some carrier proteins that shows the main role in peptide transfer included: Pept1 (intestinal oligopeptide transporter), PepT2 (Renal oligopeptide transporter) and LEAP2 (Liver expressed antimicrobial peptide 2). This study conducted to determine the effect of using antimicrobial supplements on the transcription of intestinal peptide carriers, the performance of broiler chickens and the histological components of intestine in condition of Escherichia coli K99 contamination.

Materials and Methods:

 The experiment was designed on 400 Ross 308 broiler chicks with 8 experimental treatments including 5 replications and 20 birds per replicate. At 7 days of age, 10 pieces of each broiler chickens were isolated and inoculated with 107 Escherichia coli K99 pathogenic bacteria in a 2-times with interval of 3 days. Following the inoculation, the treatments were divided into two groups: challenged with Escherichia coli K99 and no challenge. The treatments were: 1- Basal diet (control), 2- Basal diet and probiotics (Lactobacillus salivarius and Lactobacillus plantarum, 109 cfu / kg) 3- Basal diet and herbal supplement with X-Tract (Pancosma LTD, Geneva, Switzerland) (a mixture of 2% thyme extract, 2% pepper and 5% cinnamon) 100 grams per ton in granular powder 4 - Basal diet and Oxytetracycline antibiotic 200-400 g per ton fed for 2 weeks. Body weight, feed intake, FCR and daily body weight gain was recorded at 10, 24 and 42 days. Chickens were slaughtered at 14 days and 21 days and  jejunum and liver tissues sampled for gene expression and histomorphological evaluation respectively. Expression of PepT1and PepT2 in the jejunum and LEAP2 in the liver were measured and GAPDH was used as reference gene. Real time PCR reactions were done by ABI 7300 instrument. The chickens were brood based on Ross 308 manual (2014) and performance of birds include of body weight, average daily gain, feed intake and feed conversion ratio (FCR) were measured after end of each breeding period. The experiment was performed by completely random design in 8 treatments and analyzed by a 2*4 factorial method including challenge (2 levels) and supplement (4 levels) factors. The data was analyzed using SAS 9.2 with GLM procedure and the means compare by Tukey test.

Results and discussion :

The results of this study showed that the average daily gain in the probiotic group increased significantly in the challenge condition during the period of 11 to 24 days. In 25-42 period, the chickens were fed the diet contained probiotic showed the highest average daily gain although, there was no significant difference between the treatments in this period. In addition, the use of probiotic supplementation in challenge condition during the period of 11 to 24 days showed an increase in feed intake, which was similar to that of the control group in healthy group. The herbal supplement reduced daily intake in period of 11 to 24 days compared to other treatments. The use of probiotic in the feed under challenge induced a significant increase in the villi's height in jejunum. The supplementation of Lactobacillus plantarum and Lactobacillus salivariuos increased the width of villi on intestinal epithelium more than the other treatments. Depth of crypt of lieberkuhn was the least in the chickens feed by herbal supplement of X-tract.  The expression levels of PepT1 and PepT2 transcripts in the intestinal tract and the LEAP2 transcript in the liver, it was shown that challenge in the chickens fed by supplements reduced the PepT1 expression whereas expression of this gene increased in control treatment. Similar interaction was observed in PepT2 expression except for chicken fed by herbal supplement that showed an effect similar to control. Expression of LEAP2 reduced in all treatments under challenge with the E .coli, in comparison to healthy groups but reduction was minimum in the chickens fed by diet contained with probiotic.

Conclusion:

 The results of this study suggested that the use of probiotic supplement can decrease the risk effects of microbial challenge and recovery period was probably shortened using probiotic in the diet.