Disentangling the metabolic profile of rumen ciliates: A historical perspective and future directions

•Review of rumen ciliate metabolism highlights the evolution of analytical approaches over the last decades and outlines future directions.•Microscopy and modern genomics provide deeper insights into the metabolism of rumen ciliates, with each group related to specific functions.•Understanding rumen ciliate metabolism can enhance feed efficiency and promote more sustainable livestock production. Rumen ciliates constitute a highly diverse group within the subclass Trichostomatia. They are known for their symbiotic relationship with ruminant hosts and their pivotal role in digestive metabolism. This review presents a historical analysis of research on rumen ciliate metabolism, since the earliest studies, based on in vitro and in situ experiments, as well as molecular studies, initially relying on Sanger sequencing, and more recently, next-generation sequencing techniques. Finally, the paper discusses future approaches that may be useful for elucidating the metabolic profile of various taxa of rumen ciliates.