Ruminants digest plant biomass more efficiently than monogastric animals due to their symbiotic relationship with a complex microbiota residing in the rumen environment. What remains unclear is the relationship between the rumen microbial taxonomic and functional composition and feed efficiency (FE), especially in crossbred dairy cattle (Holstein x Gyr) raised under tropical conditions. In this study, we selected twenty-two F1 Holstein x Gyr heifers and grouped them according to their residual feed intake (RFI) ranking, high efficiency (HE) (n= 11) and low efficiency (LE) (n= 11), to investigate the effect of FE on the rumen microbial taxa and their functions. Rumen fluids were collected using a stomach tube apparatus and analyzed using amplicon sequencing targeting the 16S (bacteria and archaea) and 18S (protozoa) rRNA genes. Alpha-diversity and beta-diversity analysis revealed no significant difference in the rumen microbiota between the HE and LE animals. Multivariate analysis (sPLS-DA) showed a clear separation of two clusters in bacterial taxonomic profiles related to each FE group, but in archaeal and protozoal profiles, the clusters overlapped. The sPLS-DA also revealed a clear separation in functional profiles for bacteria, archaea, and protozoa between the HE and LE animals. Microbial taxa were differently related to HE (e.g.,HowardellaandShuttleworthia) and LE animals (e.g.,EremoplastronandMethanobrevibacter), and predicted functions were significatively different for each FE group (e.g., K03395—signaling and cellular process was strongly related to HE animals, and K13643—genetic information processing was related to LE animals). This study demonstrates that differences in the rumen microbiome relative to FE ranking are not directly observed from diversity indices (Faith’s Phylogenetic Diversity, Pielou’s Evenness, Shannon’s diversity, weighted UniFrac distance, Jaccard index, and Bray–Curtis dissimilarity), but from targeted identification of specific taxa and microbial functions characterizing each FE group. These results shed light on the role of rumen microbial taxonomic and functional profiles in crossbred Holstein × Gyr dairy cattle raised in tropical conditions, creating the possibility of using the microbial signature of the HE group as a biological tool for the development of biomarkers that improve FE in ruminants.

Productive performance for silage production of five forage sorghum genotypes (BRS Ponta Negra, BRS 655, BR 601, BRS 506 and BRS 610) was evaluated through the yield of dry matter, digestible dry matter, and fresh matter, plant height, percentage of lodged and broken plants, and anatomical fractions in Brazilian semi-arid region. BRS 506 and BRS Ponta Negra varieties achieved the highest fresh forage yields (89.4 and 76.2 ton. ha^-1), and BRS 506, stood out for dry and digestible dry matter yield (25.2 and 12.1 ton. ha^-1, respectively). Regarding the participation of the plant fractions, BRS 655 and BRS 610 genotypes showed a higher percentage of panicles (50.2 and 41.0% respectively), while BRS 506 stressed out the stem participation (84.6%), and BRS Ponta Negra, the leaf participation (17.9%). Among the materials evaluated for silage production, stood out the BRS 506 and BRS Ponta Negra genotypes. The results obtained for production of dry and digestible dry matter, and the ratio of plant fractions indicates the possible use of these genotypes on silage production in the Brazilian semiarid.

Background: Methane (CH₄) emissions from rumen fermentation are a significant contributor to global warming. Cattle with high CH₄ emissions tend to exhibit lower efficiency in milk and meat production, as CH₄ production represents a loss of the gross energy ingested by the animal. The objective of this study was to investigate the taxonomic and functional composition of the rumen microbiome associated with methane yield phenotype in dairy cattle raised in tropical areas. Methods and results: Twenty-two Girolando (F1 Holstein x Gyr) heifers were classified based on their methane yield (g CH₄ / kg dry matter intake (DMI)) as High CH₄ yield and Low CH₄ yield. Rumen contents were collected and analyzed using amplicon sequencing targeting the 16 and 18S rRNA genes. The diversity indexes showed no differences for the rumen microbiota associated with the high and low methane yield groups. However, the sparse partial least squares discriminant analysis (sPLS-DA) revealed different taxonomic profiles of prokaryotes related to High and Low CH₄, but no difference was found for protozoa. The predicted functional profile of both prokaryotes and protozoa differed between High- and Low CH₄ groups. Conclusions: Our results suggest differences in rumen microbial composition between CH₄ yield groups, with specific microorganisms being strongly associated with the Low (e.g. Veillonellaceae_UCG − 001) and High (e.g., Entodinium) CH₄ groups. Additionally, specific microbial functions were found to be differentially more abundant in the Low CH₄ group, such as K19341, as opposed to the High CH₄ group, where K05352 was more prevalent. This study reinforces that identifying the key functional niches within the rumen is vital to understanding the ecological interplay that drives methane production.

Anaerobic fungi (phylum Neocallimastigomycota) play a crucial role in degrading forages and fibrous foods in the gastrointestinal tract of mammalian herbivores, particularly ruminants. Currently, they are classified into twenty-two genera; however, recent research suggests the occurrence of several novel taxa that require further characterization. Anaerobic rumen fungi play a pivotal role in lignocellulose degradation due to their unique enzymatic capabilities. This review explores the enzymatic systems of rumen anaerobic fungi, highlighting their ability to produce a diverse array of carbohydrate-active enzymes (CAZymes), such as cellulases, hemicellulases, and pectinases. These enzymes facilitate the breakdown of complex plant polymers, making anaerobic fungi essential contributors to fiber degradation in the rumen ecosystem and valuable resources for biotechnological applications. This review summarizes the structural and functional diversity of fungal CAZymes, and the mechanical disruption of plant cell walls by fungal rhizoidal networks is discussed, showcasing the ability of fungi to enhance substrate accessibility and facilitate microbial colonization. Recent studies using genomic, transcriptomic, and biochemical approaches have uncovered several novel CAZymes in anaerobic fungi, including multifunctional xylanases, β-glucosidases, and esterases. These findings highlight the continued expansion of fungal enzyme repertoires and their potential for biotechnology and feed applications. Continued research in this field will enhance our understanding of microbial ecology and enzyme function, paving the way for applications that address global challenges in energy, food security, and environmental sustainability.

The rumen is one of the four compartments of the ruminant stomach and houses a diverse array of anaerobic microbes that play a crucial role in feed digestion and volatile fatty acid (VFA) production. The aim of this study was to explore how two different in vivo rumen environmental conditions, AHR (created from sheep-fed alfalfa hay) and CSR (created from sheep-fed corn stover), affect fiber digestion and rumen bacterial colonization in relation to two types of forage, alfalfa hay (AH) and corn stover (CS). Both AH and CS forages were subjected to in-sacco incubation in AHR and CSR conditions for a period of 48 h. The results revealed that CSR exhibited a less variant pH, lower total VFA concentration, and higher acetate-to-propionate ratio than AHR. CSR significantly enhanced the degradation of neutral detergent fiber and acid detergent fiber in both incubated forages (AH and CS). Although CSR did not improve the degradation of dry matter (DM) or crude protein (CP) on AH, it improved the degradation of DM and CP on CS. Both CS and AH incubated under CSR were found to have a greater abundance of fibrolytic bacteria (e.g., Fibrobacter and Butyrivibrio 2) compared to the same forage incubated under AHR, especially during the initial stages of incubation. However, CS and AH incubated under AHR were colonized by bacteria specialized in breaking down soluble carbohydrates (e.g., Prevotella and Succinivibrio). Compared with AHR, CSR enhanced the degradation rates of both incubated forages (CS and AH). These findings underscore the role of the rumen microenvironment in affecting the composition of adherent microbial communities and enhancing the breakdown of forages. Therefore, optimizing the rumen microenvironment to promote the attachment of fibrolytic bacteria during the early fermentation stages while minimizing hydrogen accumulation to stabilize the pH could lead to improved forage fermentation and animal performance.