Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, PC241
Effect of dietary linoleic acid on UT-B urea transporter abundance in the bovine rumen.
G. Stewart1, A. De Bhulbh1, K. Petrie2, T. Boland2
1. School of Biology and Environmental Science, University College Dublin, Dublin, Ireland. 2. School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Dublin, Ireland.
The livestock industry is responsible for the production of vast quantities of methane, a potent greenhouse gas. Methane is produced as a by-product of the fermentation processes that occur within the rumen of animals such as cattle and sheep. Previous research has suggested that supplementing animal diets with linoleic acid reduces methane production (Boland et al., - unpublished data), although the mechanism for this action is unclear. Ruminal fermentation requires the recycling of nitrogen through the process of urea nitrogen salvaging (Stewart & Smith, 2005), which involves large amounts of urea entering the rumen via facilitative UT-B urea transporters (Stewart et al., 2005). We have previously shown that expression of UT-B transporters situated in the ruminal papillae can be regulated by dietary intake (Simmons et al., 2009). We therefore investigated the effect of dietary linoleic acid on UT-B transporter abundance in the bovine rumen. Adult beef cattle were fed a concentrate-based diet supplemented with (i) 6% stearic acid, (ii) 6% linoleic acid, or (ii) 3% stearic acid plus 3% linoleic acid. The various diets had no effect on ruminal fluid content, with no significant changes in either ammonia or volatile fatty acid concentration (NS, N = 12, ANOVA). Western blot analysis showed that the dietary changes also had no effect on the relative expression of UT-B transporters in ruminal papillae, either in plasma membrane-enriched protein samples (NS, N = 3, ANOVA) or cytosolic-enriched protein samples (NS, N = 3, ANOVA). However, the diet containing 6% linoleic acid significantly reduced the average length of the ruminal papillae (P < 0.05, N = 12, ANOVA) without changing papillae density (NS, N = 6, ANOVA). These data show that although dietary supplementation with linoleic acid had no effect on the relative expression of UT-B transporters in bovine rumen tissue per se, it decreased the average papillae length and hence the overall ruminal epithelial surface area. It can therefore be extrapolated that the total abundance of urea transporters in the bovine rumen would be decreased. Further research is now required to investigate whether this change leads to reduced trans-epithelial movement of urea and reduced ruminal fermentation, as this would explain the previously observed changes in methane production.
Where applicable, experiments conform with Society ethical requirements