|AGARWAL, UMANG - BAYLOR COLLEGE OF MEDICINE|
|HU, QIONG - UNIVERSITY OF MARYLAND|
|Baldwin, Ransom - Randy|
|BEQUETTE, BJ - UNIVERSITY OF MARYLAND|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2015
Publication Date: 4/20/2015
Citation: Agarwal, U., Hu, Q., Baldwin, R.L., Bequette, B. 2015. Role of rumen butyrate in regulation of nitrogen utilization and urea nitrogen kinetics in growing sheep. Journal of Animal Science. 93:2382-2390. DOI: 10.2527/jas.2014-8738.
Interpretive Summary: Inefficiency of use of nitrogen (N) is a major production concern for ruminant producers. Butyrate is a naturally occurring end product of feed degradation in the rumen that has many apparent beneficial impacts on N and whole body nutrient use. Our objective was to investigate the direct effect of elevating ruminal butyrate on urea-N recycling, overall N utilization and rumen tissue protein turnover rate, and thus to provide direct evidence of a role for butyrate in upregulation of urea-N transfer to the rumen. Butyrate was not found to improve overall N retention in sheep in these short experiments however butyrate did alter urea synthesis and changed urea-N fluxes. Butyrate may be acting via a number of mechanisms such as by impacting microbial growth dynamics and changing rumen ammonia fluxes to enhance the capture of recycled urea-N in the rumen. Furthermore, butyrate substantially increased the rate of protein synthesis occuring in the rumen tissue. Ultimately, the mechanisms regulating movements of N into and out of the rumen are complex and multiple factors determine the net capture of recycled urea-N. These studies are the first to directly assess the role of butyrate in urea recycling and its effects on rumen tissue protein turnover in growing lambs.
Technical Abstract: Butyrate, a major rumen VFA, has been indirectly linked to enhancement of urea recycling based on increased expression of urea transporter (UT-B) in the rumen epithelia of steers fed a rumen butyrate-enhancing diet. Two studies were conducted to quantify the effect of elevated rumen butyrate concentrations on N balance, urea kinetics and rumen epithelial proliferation. Wether sheep (n=4), fitted with a rumen cannula, were fed a pelleted ration at 1.8 × maintenance energy intake (130 g CP/kg, 9.3 MJ ME/kg). In Exp. 1, sheep were infused intra-ruminally with either an electrolyte buffer solution (Con-Buf) or butyrate dissolved in the buffer solution (But-Buf) during 9-d periods in a balanced crossover design. In Exp. 2, sheep were infused intra-rumianlly with either sodium-acetate (Na-Ac) or sodium butyrate (Na-But). All solutions were pH adjusted and VFA were infused at 10% of ME intake. [15N2]urea was continuously infused i.v. for the last 5 d of each period, and total urine and feces collected. In Exp. 1, [ring-D5]phenylalanine was continuously infused i.v. over the last 12 h, after which a biopsy from the rumen papillae was taken for measurement of fractional protein synthesis rate (FSR). Butyrate infusion treatments increased (P = 0.1 in Exp. 1; P < 0.05 in Exp. 2) the proportion of rumen butyrate, and acetate infusion increased (P < 0.05) rumen acetate. All animals were in positive N balance (4.2 g N/d in Exp. 1; 7.0 g N/d in Exp. 2), but no difference in N retention was observed between treatments. In Exp. 2, urea entry (synthesis) rate was reduced (P < 0.05) by Na-But compared to the Na-Ac control. As a result, a higher proportion of urea-N entering the rumen was utilized for microbial protein synthesis in Exp. 2 with Na-But infusion. In Exp. 1, although But-Buf infusion increased the FSR of rumen papillae (35.3 ± 1.08 %/d vs 28.7 ± 1.08 %/d, P < 0.05), urea kinetics were not altered by But-Buf compared to Con-Buf. These studies are the first to directly assess the role of butyrate in urea recycling and its effects on rumen papillae protein turnover in growing lambs. Under the feeding conditions used and the rate of continuous butyrate infusion into the rumen in the present studies, butyrate does not affect overall N retention in growing sheep. However, butyrate may play a role in regulating urea synthesis and thereby affect the redistribution of urea-N fluxes in the overall scheme of N metabolism.