Effect of barley and its amylopectin content on ruminal fermentation and bacterial utilization of ammonia-N in vitro

The objective of this study was to determine the effect of variety and amylopectin content of barley on ruminal fermentation and ammonia-N utilization by mixed ruminal bacteria in vitro. Three barley varieties (WestBred Gustoe, Nebula, Baronesse) and their waxy counterparts were tested. The control grain was corn. All barley varieties were examined at three substitution levels: 25, 50, and 75% with the remaining being corn. Ammonia-N was labeled with 15N-ammonium sulfate. Samples were collected at 0, 2, 4, 6, and 8 h. Barley inclusion enhanced (P<0.05) propionate production and total VFA at the 75% substitution level and, at 8 h, increasing the proportion of barley in the grain mix increased (P<0.05, linear effect) propionate concentration and decreased (P<0.05, linear effect) acetate to propionate ratio. Across sampling points, the waxy variety of WestBred Gustoe resulted in higher (P<0.05) fluid bacteria incorporation of ammonia-N than corn (by 7.6 and 11.9%, 25 and 75% substitution levels, respectively). At the 75% substitution level, waxy barleys resulted in an 8% higher (P<0.01) ammonia-15N incorporation into bacterial N than their non-waxy counterparts. At the end-point of the incubation, barley treatments and waxy barleys had higher (P<0.05) 15N-enrichment of the fluid bacterial N compared with corn and non-waxy barleys, respectively. The combined (fluid- and particle-associated bacteria and protozoa) microbial ammonia-N uptake, however, was not different between corn control and treatments with barley. Results suggest that ruminal responses to barley supplementation may vary depending on its variety and starch composition and differ between fluid- and particle-associated microorganisms.