By Joana Lima

Ruminants can be fed on human-undigestible plant biomass due to the symbiotic relationship they maintain with the microorganisms that inhabit their rumen. The microbiota (collection of bacteria, protozoa, and fungi) is able to ferment complex polysaccharides in the feed, producing volatile fatty acids, microbial protein, and vitamins, that are absorbed by the host animal and utilized for maintenance, development and growth.

Nematode parasites are one of the most important factors adversely impacting the economy of cattle production systems. O. ostertagi is an abomasal parasitic nematode that impairs the gastrointestinal function of the host, associated, for example, with reduced appetite in dairy cattle, leading to hindered growth rates and even possibly the death of the animal. Cattle takes a long time to develop immunity to O. ostertagi, and animals can be susceptible to infection even after long grazing periods (when they ingest the nematode larvae that rests in herbal pats). Usually, helminths such as O. ostertagi are controlled using anthelminthics, but the potential development of resistant parasites makes vaccination a much more attractive strategy. The ideal vaccine should strengthen the animal’s immune response to the parasite while having no negative effects on the rumen microbiota (as to not reduce productivity).

Researchers of the Host Genetics and Microbiome Research group at the Scottish Rural College (SRUC), together with researchers at the Moredun Research Institute and University of Edinburgh, investigated the rumen microbiota of vaccinated, infected animals with low cumulative faecal egg count and with high cumulative faecal egg count and compared those to the microbiota of uninfected, non-vaccinated animals. This project is being undertaken by PhD student Joana Lima, supervised by Professor Rainer Roehe.

In comparison to uninfected animals, the abundance of 314 and 294 microbes were found to be altered in infected animals with low cumulative faecal egg count and with high cumulative faecal egg count, respectively. Additionally, the vaccine altered the abundance of 330 microbes. For example, infected animals showed decreased abundances of Paenibacillus, which is a hemicellulose-degrading bacterium, and Butyrivibrio and Pseudobutyrivibrio, which utilize xylans and pectins, and ferment carbohydrates into butyrate, formate, lactate and acetate, being important energy suppliers to ruminants. In vaccinated animals, we observed depletion of Prevotella, and enrichment of several groups of fungi, including potential pathogens such as Colletotrichum, Paracoccidioides and Exophiala.

These results show that the parasite presence greatly influences the rumen microbiota in dairy cattle, suggesting that the impairment observed in infected animals is not solely a consequence of the parasite physical damage in the gastrointestinal tract, but it is also due to alterations to the rumen fermentation profile. Additionally, the vaccine was also found to influence the composition of the rumen microbiota, underlining the importance of including microbiota information in future vaccine-development studies.