Multi-omics reveals that forage fiber promotes rumen development of pre-weaning calves compared to non-forage fiber

Abstract

Background: The rumen development of calves can result in long-term effects on growth, health, and milk yields in adult cattle. Dietary fiber supplement can stimulate rumen development in calves during pre-weaning period. Non-forage fiber can be used as starter fiber to reduce gastrointestinal fill and increase the content of rumen volatile fatty acid (VFA) because of higher biodegradable fiber. Numerous studies revealed that non-forage fiber has no negative effect on pre-weaning calves compared to forage fiber, but few evidences of rumen development were given. It is unclear whether different fiber sources impact the development of rumen in pre-weaning calves. Here, this study investigated the synergistic responses of rumen microbiota, metabolites and epithelium to different fiber source. Results: Thirty healthy Holstein calves with similar age (4.2 ± 2.3 days) and body weight (39.2 ± 3.6 kg) were allocated to two groups (15 cows per group), and were fed with one of the two diets with different fiber sources, short oat hay (SO), or short soybean hull (SS) for 8 weeks, respectively. At the end of the experiment, 6 calves of each group with similar body weight were selected to slaughter. Observations showed that SO-feeding calves has lengthened and widened rumen epithelial papillae. Metagenomic results revealed that different bacteria responded to different fiber source by different Carbohydrate-active enzymes (CAZymes) (P < 0.05). Metabolomics analysis indicated that “vitamin B6 metabolism” pathway was significantly enriched based on the 22 increased metabolites in the SO calves (P < 0.05, pathway impact > 0.05). The Pyridoxine, 4a-Carbinolamine tetrahydrobiopterin and Gentisic acid were enriched under SO feeding (P < 0.05, VIP > 1). Transcriptome analysis revealed that 129 differentially expressed genes (DEGs) were identified from comparison of the two groups. The DEGs related to transcription, translation and energy metabolism were upregulated (P < 0.05). Conclusions:The SO feeding (forage fiber) can lead to the enrichment of beneficial metabolites and metabolic pathways, promote the expression of genes related to energy metabolism, transcription and translation, and ultimately promote the development of rumen epithelium. Therefore, in pre-weaning calves production, attention should be paid to the impacts of forage fiber (short oat hay) introduction on rumen morphology and function.