Background: Hair fibre length is an important economic trait of rabbits in fur production. However, molecular mechanisms regulating rabbit hair growth have remained elusive. Results: Here we aimed to characterise the skin traits and gene expression profiles of short-hair and long-hair rabbits by histological and transcriptome analyses. Haematoxylin-eosin staining was performed to observe the histological structure of the skin of short-hair and long-hair rabbits. Compared to that in short-hair rabbits, a significantly longer anagen phase was observed in long-hair rabbits. In addition, by RNA sequencing, we identified 951 genes that were expressed at significantly different levels in the skin of short-hair and long-hair rabbits. Nine significantly differentially expressed genes were validated by quantitative real-time polymerase chain reaction. A gene ontology analysis revealed that epidermis development, hair follicle development, and lipid metabolic process were significantly enriched. Further, we identified potential functional genes regulating follicle development, lipid metabolic, and apoptosis as well as important pathways including extracellular matrix-receptor interaction and basal cell carcinoma pathway. Conclusions:The present study provides transcriptome evidence for the differences in hair growth between shorthair and long-hair rabbits and reveals that lipid metabolism and apoptosis might constitute major factors contributing to hair length.

The transcriptome is the complete set of transcripts for certain type of cells or tissues in a specific developmental stage or physiological condition. Transcriptome analysis can provide a comprehensive understanding of molecular mechanisms involved in specific biological processes and diseases from the information on gene structure and function. Transcriptome has been challenging due to the efficient and fast procedures of RNA-seq. RNA-seq, refers to the use of high-throughput sequencing technologies to sequence cDNA library transcribed from all RNAs in tissues or cells, can be used to quantify, profile, and discover RNA transcripts by sequence reads. Thus, the transcripts can then be mapped on the reference genome to get comprehensive genetic information, such as transcription localization and alternative splicing status. RNA-Seq has been widely used in biological, medical, clinical and pharmaceutical research. The detailed principles, technical characteristics and applications of RNA-seq are reviewed here, and the challenges and application potentials of RNA-seq in the future are also discussed. This will present the useful information for other researchers.

In contrast to colostral immunoglobulins, changes in metabolite composition of ingested colostrum in the gut have received little attention. Here, we characterized the metabolite profiles of colostrum and milk, ingested colostrum and milk, and serum of neonatal calves by liquid chromatography tandem-mass spectrometry and gas chromatography-mass spectrometry metabolomics approaches. Colostrum and milk underwent similar changes in metabolite profiles in the gut after being ingested. These changes were characterized by increases in methionine, glutamate, thymine, and phosphorylcholine. After ingestion, colostrum concentrations of several metabolites, such as γ-aminobutyric acid, glutamate, cinnamic acid, and thymine increased, whereas concentrations of d-ribose, and arginine decreased. These increases and decreases occurred in a time-dependent manner and were associated with alanine, aspartate, glutamate, and pyrimidine metabolism, and valine, leucine, and isoleucine biosynthesis, respectively. Meanwhile, similar changes in serum metabolites were also observed in neonatal calves fed colostrum, which implies that colostrum metabolites are transported across the small intestine and into the bloodstream. In addition, several metabolites of ingested milk were detected in the gut, and were also transferred to the bloodstream. These metabolites were related to phenylalanine, tyrosine, tryptophan, valine, leucine, and isoleucine biosynthesis, the citrate cycle, and histidine metabolism. These findings reveal that the serum metabolome of neonatal calves' changes as a result of ingesting colostrum, which can provide health-related benefits in early life.

Casein micelles contribute to the physicochemical properties of milk and may also influence its functionality. At present, however, there is an incomplete understanding of the casein micelle associated proteins and its diversity among the milk obtained from different species. Therefore, milk samples were collected from seven dairy animals groups, casein fractions were prepared by ultracentrifugation and their constituent proteins were identified by liquid chromatography tandem mass spectrometry. A total of 193 distinct proteins were identified among all the casein micelle preparations. Protein interaction analysis indicated that caseins could interact with major whey proteins, including β-lactoglobulin, α-lactalbumin, lactoferrin, and serum albumin, and then whey proteins interacted with other proteins. Pathway analysis found that the peroxisome proliferator-activated receptor signaling pathway is shared among the studied animals. Additionally, galactose metabolism pathway is also found to be commonly involved for proteins derived from camel and horse milk. According to the similarity of casein micelle proteomes, two major sample clusters were classified into ruminant animals (Holstein and Jersey cows, buffaloes, yaks, and goats) and non-ruminants (camels and horses). Our results provide new insights into the protein profile associated with casein micelles and the functionality of the casein micelle from the studied animals.