PSIV-4 - Effects of Passage Rate on Rumen Microbial Composition

Abstract: The objective was to evaluate the effects of dietary treatments designed to increase passage rate on the rumen microbiome. Factors such as particle size, feedstuff degradability, and rumen motility may drive ruminal passage rates and alter the composition of rumen microorganisms responsible for methane formation. Eight ruminal-cannulated steers were assigned to a replicated 4 × 4 Latin square design. All steers were fed an ad libitum diet of prairie grass hay (10.4% crude protein) with treatments designed to increase passage rate: no treatment (CON), pelleted (PEL), 7% Ca(OH)₂ treated (ALK), and six 2 kg weights inserted into the rumen (WTS). Ruminal contents were collected on day 13 for 16S rRNA sequencing using specific bacterial and archaeal primers. Bacterial and archaeal taxa were not different (P > 0.1) between WTS and CON. At the genus level, PEL-fed steers had decreased (P = 0.01) relative abundance of Butyrivibrio 2 when compared with CON. Steers fed ALK had decreased (P < 0.01) relative abundance of Rikenellaceae RC9 gut group but increased (P < 0.01) Christensenellaceae R-7 group compared with CON. In contrast, relative abundance of Christensenellaceae R-7 group decreased (P = 0.03) in steers fed PEL compared with CON. The most abundant archaea, Methanobrevibacter, increased (P = 0.04) in steers fed ALK compared with CON (75 vs 65% of archaeal reads, respectively). Additionally, relative abundance of Methanosphaera increased (P < 0.01) in steers fed PEL compared with CON. Measures of richness including Chao1 and observational taxonomic units were decreased (P < 0.01) in ALK-treated steers but were not affected (P > 0.2) by PEL or WTS compared with CON. In conclusion, pelleting and alkali treatment of hay affected the rumen microbiome composition compared with steers fed basal prairie grass hay. Increased passage rates may alter composition of rumen bacteria and archaea communities.