Inoculation with rumen fluid in early life accelerates the rumen microbiome development and favours the weaning process. Inoculation with rumen fluid in early life accelerates the rumen microbiome development and favours the weaning process

Newborn ruminants possess an underdeveloped rumen ecosystem which needs to be colonized by rumen-adapted microorganisms present in older animals. This microbial transfer can limit rumen microbial development in dairy systems in which newborns are separated from their dams at birth. This study explores whether the direct inoculation of fresh or autoclaved rumen fluid from adult goats to newborn kids has a beneficial effect on rumen microbial development and function. Inoculation of young animals with fresh rumen fluid from adult animals adapted to forage (RFF) or concentrate diets (RFC) accelerated the rumen microbial colonization during the pre-weaning period leading to high protozoal numbers, a more biodiverse bacterial (+234 OTUs), methanogens (+6 OTUs) and protozoal communities (+25 OTUs) and greater size of the core microbial communities than observed in control animals (CTL). This inoculation also increased the core bacterial and methanogens communities and increased the abundance of key rumen bacteria, methanogens, anaerobic fungi and protozoal taxa before weaning whereas control animals remained protozoa-free through all study. Most of these taxa were positively correlated with indicators of the rumen microbiological (higher bacterial, methanogens and protozoal richness and protozoal concentration) and physiological development (higher forage and concentrate intakes and animal growth during the post-weaning period) favouring the weaning process in RFF and RFC animals in comparison to CTL animals. Some of these microbiological differences tended to decrease during the post-weaning period, although RFF and RFC animals still retained a more complex and matured rumen microbial ecosystem than CTL animals. Inoculation with autoclaved rumen fluid promoted lower developments of the bacterial and protozoal communities during the pre-weaning period than using fresh inocula, but it favoured a more rapid microbial development during the post-weaning than observed for CTL animals. This study demonstrated that repetitive inoculation of young ruminants with fresh rumen fluid from adult animals accelerated rumen microbial colonization which was associated with an earlier rumen functional development. This strategy facilitated a smooth transition from milk to solid feed and could favor the implementation of early weaning strategies.