Grain grinding size of cereals in complete pelleted diets for growing lambs: Effects on ruminal microbiota and fermentation

•Effects of cereal grinding size on rumen function were evaluated in fattening lambs.•Finely ground cereals increase abundance of ruminal bacteria related to acidosis.•Coarser cereal particle size is related to enhanced status of rumen mucosa.•Cereal particle size affects the fatty acid profile of ruminal digesta.•Increasing cereal grinding size may reduce ruminal acidosis in fattening lambs.