Effect of Monensin and plant extract on rumen and blood metabolites and gene expression of the urea transporter gene in the rumen epithelium of fattening lambs

Urea as the final product of nitrogen metabolism plays a pivotal role in ruminants’ nitrogen economic efficiency (Marini and Van Amburgh, 2003). Ruminants are capable to recycle and return a tremendous amount of urea to rumen rather than excretion to urine; the recycled urea is hydrolyzed to CO2 and ammonia and thereafter is used for the synthesis of microbial protein (Harmeyer and Martens, 1980). By changing ruminal and blood metabolites, Monensin and herbal extracts can change and modify the expression of urea transporter gene in rumen epithelium. Monensin is an ionophore antibiotic which changes the ratio of VFAs in the rumen in favor of propionic acid and decreases the production of methane (Duffield and Bagg, 2000). The aim of present study was to investigate the effects of Monensin and herbal extracts as feed additives on type B urea transporter gene in rumen epithelium and also on ruminal ammonia, VFAs, pH and blood ammonia in fattening lambs.
Material and In this experiment 16 Afshari ram lambs with initial BW of 41±5.6 kg and 6 months of age were used. The lams were randomly assigned to four experimental dietary treatments in a completely randomized design; 1) no additive (control), 2) 30 mg monensin.d-1 per lamb, 3) periodical inclusion of 30 mg monensin.d-1 per lamb, and 4) 2 g of a commercial blend of plant extract.d-1 per lamb. During the experiment, lambs were kept in individual boxes and the diets and fresh drinking water were offered ad libitum. 3 weeks were considered as an adaptation to diets and 8 weeks were considered as an experimental period in which treatments and samplings were conducted. The forage: concentrate ratio was set to 20:80 and the rations were prepared daily, mixed by hand and were offered two times at 09:00 and 16:00. Two hours after morning feeding rumen samples were collected every other 2 weeks by using a special tube and electrical vacuum pump. Also, immediately after slaughtering and before skinning 2 rumen samples were collected, filtered and the pH was determined. 8 ml of the first sample was mixed with 2 ml of % 25 sulfuric acid for measurement of ammonia and 8 ml of the second sample was mixed with %25 meta-phosphoric acid for measurement of VFAs. The mixed samples were kept in -20ºC until assays. After thawing, rumen samples were centrifuged for 10 to 15 min and then the supernatant was separated and stored for FAs and ammonia measurements. Blood and rumen samples were collected before slaughtering and rumen tissue samples were taken from ventral part of the rumen. VFA in rumen samples was measured by using Gas chromatograph (Mirzaei-Alamouti et al. 2016). The ammonia nitrogen was measured by using a spectrophotometer. Blood samples were taken at the beginning of the experiment and then every 2 weeks after the morning feeding into heparinized tubes. Blood samples were centrifuged at 3000 rpm for 15 min and plasma samples were stored at -20º C for plasma urea nitrogen. Blood urea nitrogen was measured with commercial kits using a spectrophotometer. The lambs were slaughtered 56 days after feeding with experimental diets and the tissue samples were taken from ventral part of the rumen. Relative gene expression of UT-B was determined by Real-time PCR technique (Mirzaei_Alamouti et al, 2016). Experimental data were subjected to analysis of variance by the mixed procedure of SAS (9.1).
The relative expression of urea transporter gene in lambs fed with periodical Monensin was 0.167 in comparison to control group. In Pfaffl’s (2001) method, the gene expression in control group is considered 1; thus, the expression of urea transporter gene in periodical Monensin group has been reduced (P all in all, the results of this study showed an inverse or average relationship between urea transporter gene expression with ammonia nitrogen, butric acid and valeric acid and a positive relationship with VFAs. The periodical inclusion of Monensin to the diets may change the rumen fermentation and reduce the expression of urea type B transporter. In comparison to this, the continued inclusion of Monensin to the diets would improve rumen fermentation and increase the expression of the urea-type B transporter gene. The herbal extract used in this study may change the rumen fermentation but is not possibly effective on epithelial cells which are involved in urea transportation. In this study, the rumen variables were more effective in urea transportation in compare to blood variables.