Increasing Rumen Microbial Diversity in Goats Favours the Adaptation to High‐Concentrate Diets With Minor Effects on Feed Utilization

Evolution has enabled ruminants to develop a complex rumen microbiota that aids in the digestion of fibrous feeds. This study examines whether promoting a highly diverse rumen microbiota during early life continues to offer long-term benefits in modern dairy production systems, where young ruminants are reared without exposure to adult ruminants and are fed high-concentrate diets. A total of 36 newborn goat kids were divided in 4 groups. During the first 10 weeks of age, animals were daily inoculated with autoclaved rumen fluid (AUT), fresh rumen fluid from adult goats fed forage (RFF), or concentrate diet (RFC), or received no inoculation (CTL). At 29 weeks of age, following an 18-week wash out period, the animals were shifted from a full-forage to a high-concentrate diet to assess their ability to adapt and digest this later diet. Results revealed that early life inoculation with fresh rumen fluid had a lasting effect on the rumen microbiota, promoting higher bacterial (+93 OTUs), methanogens (+5 OTUs) and protozoal diversity (+23 OTUs), whereas CTL animals remained protozoa-free. This superior microbial complexity accelerated the adaptation to high-concentrate diets, decreased digestive disorders (rumen acidosis and diarrhoea) and increased BW gain. Once adapted to the diet, inoculated animals exhibited higher rumen VFA concentration (+16%), blood glucose (+28%), rumen papillae width (+43%) and increased expression of rumen epithelium genes involved in the cell proliferation (Cyclin 1), VFA absorption (MCCT1) and VFA metabolism (HMGCL), suggesting an enhanced energy uptake capacity. Inoculation with autoclaved rumen fluid as source of VFA had lower long-term effects compared to fresh inocula. No differences across treatments were noted for feed digestibility, N excretion, and microbial protein synthesis. In conclusion, promoting greater rumen microbial diversity is a desirable strategy to prevent digestive disorders during the adaptation process to high-concentrate diets, having minor effects once the animals are adapted to this diet.