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Supplementation of Aspergillus oryzae α-amylase on ruminal volatile fatty acid distribution and digestive tract gene expression in beef steers fed a steam-flaked corn based finishing diet
The objective of this study was to investigate the impact of Aspergillus oryzae α-amylase (AAM) supplementation on rumen VFA profile and relative abundance of mRNA associated with nutrient absorption in ruminal and duodenal tissue from beef steers. Nine crossbred steers (average BW 622 ± 50 kg), with rumen and duodenal fistulas were housed in individual stations and fed a high concentrate finishing diet twice daily for 8 d. Treatments included CON (corn meal; n= 5) and AAM (750 fungal α-amylase units/g; n= 4). Dietary treatment supplements were applied as a top dress (3 g of α-amylase or corn meal into 150 g of dried distiller’s grains (DDG) for the AM feeding and 2 g of α-amylase or corn meal into 100 g of DDG for PM feeding). On d 5, rumen fluid samples were obtained every 4 h for 24 h and analyzed for VFA concentration. On d 9, rumen papillae and duodenal mucosal tissue samples were collected. Total tissue RNA was extracted for real-time PCR analysis. Sodium/potassium ATPase pump α1, glucose transporter 2 and 5, putative anion transporter, isoform1, sodium/hydrogen antiporter isoforms1, 2 and 3, 3-hydroxy 3-methylglutaryl coenzyme A synthase isoform2, down regulated in adenoma, monocarboxylate co-transporter isoform1, and glyceraldehyde-3-phosphate dehydrogenase mRNA were tested. Relative expression (fold change) of mRNA in ruminal and duodenal tissues were analyzed using PROC GLM and VFA distribution was analyzed as a randomized block design with repeated measures using the MIXED procedure of SAS. Concentrations of VFA and the acetate to propionate ratio were similar across treatments. However, acetate:propionate ratio and butyrate molar percentage were numerically greater (P = 0.17) in AAM steers compared to controls. Genes tested were not significantly changed by AAM supplementation in the rumen or duodenum. However, genes involved in nutrient absorption were numerically decreased in the rumen and increased in the duodenum in the AAM supplemented steers compared to the controls.
Keywords: duodenum, fungal α-amylase, gene, rumen, steer, volatile fatty acids