Abstract: The purpose of this study was to explore the biological characteristics of serum proteins in horses and donkeys, and to provide a theoretical basis for the comparison of the physiological characteristics among equine species and health protection. In this study, 9 Mongolian horses and 9 Liaoxi donkeys, female, aged 4-10 years old, were selected from an intensive farm in Dalian city, Liaoning province. They were all in the interestrus of normal estrous cycle. They were healthy, disease-free, mental state and eating well, and provided the same feeding conditions. Nine serum samples of horses and donkeys were collected and randomly divided into 3 groups, respectively. Three serum samples in each group were evenly mixed into one biological repeat, and 3 serum biological repeats were obtained in each group. In this study, Label-free proteomics and bioinformatics methods were used to compare the serum protein components of horses and donkeys,serum proteins were extracted, and then the proteins were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The expression of proteins in horse and donkey serum samples was analyzed by database search. The different key regulatory proteins in serum between horses and donkeys were screened by bioinformatics method.The results showed that a total of 361 proteins were identified, of which 288 proteins were identified in horse serum with molecular weight from 1.52 to 511.24 ku, and 244 proteins were identified in donkey serum with molecular weight from 1.53 to 611.47 ku, and 231 differentially expressed proteins were obtained (fold change≥1.5, P≤0.05). These proteins were mainly involved in protein activation, complement activation, immune response, regulation of coagulation and lipoprotein oxidation and other biological processes. The significantly enriched KEGG pathways included the complement and coagulation cascade, phagosome, protein processing in endoplasmic reticulum, antigen processing and presentation, metabolism of glycine, serine and threonine, proteoglycans in cancer, and so on. The interaction analysis of differentially expressed proteins showed that the most significant function modules enriched by differentially expressed proteins were metabolic pathway, complement and coagulation cascades and phagosome. HSP90AA1, HSPA8, APOD, APOM, SERPING1, MASP1, CALR, TUBA1B and TUBB were important nodes in network. There are some differences in serum protein composition between horses and donkeys under physiological conditions. This study provides a foundation for further revealing the differences of physiological characteristics among equine species and effective health protection on them.

Key words: horse, donkey, serum, Label-free, proteomic