Effects of excessive urea on rumen morphology and microbiota in Jianzhou Da'er goat (Capra hircus)

Urea is frequently used as a protein supplement in ruminant diets, but if used improperly, it can easily result in urea poisoning. The purpose of this study was to explore the effects of excessive urea feeding on rumen pathology and microbial diversity of the Jianzhou Da'er goat (Capra hircus). In this study, 9 male Jianzhou Da'er goats with an average weight of 22.9 kg were randomly divided into the control group (0% urea), 5% urea group and 10% urea group (dry matter basis, 3 goats per group). Morphological differences of rumen tissues were analyzed by Hematoxylin-Eosin staining and Prussian blue staining, and rumen microorganisms differences were analyzed by 16S rDNA sequencing on the Illumina Novaseq platform. Histopathological analysis showed that the length of rumen papilla in the 5% urea and 10% urea groups were shortened compared to the control group, and the thickness of the stratum corneum and muscular layer were significantly thinned (P < 0.05). 16S rRNA sequencing analysis indicated that microbial richness and diversity were significantly lower in goats fed on 5% urea or 10% urea, the abundance of Prevotella ruminicola was significantly decreased (P < 0.05), and the abundance of Ruminobacter amylophilus was significantly increased (P < 0.05), as compared with the control group. This study indicated that feeding 5% and 10% urea could damage rumen tissue morphology. Feeding 10% urea significantly reduced rumen microbial diversity and the abundance of Prevotella ruminicola, but increased the abundance of Ruminobacter amylophilus.