Identification of Estrus in Sows Based on Salivary Proteomics

SIMPLE SUMMARY: The conception rate of sows is an important factor affecting the efficiency and income of pig farms. At present, the traditional estrus identification methods used in production, such as the external observation method and back pressure reaction method, have the disadvantages of being time-consuming and laborious, with low accuracy and high requirements for technicians. In addition, the abnormal estrus status of sows, such as continuous estrus and short estrus, will also lead to misjudgment during estrus inspection, which will affect the conception rate of sows and reduce production efficiency. Therefore, the purpose of this study was to explore a new method for estrus identification, to provide an important reference for accurate estrus identification of sows by screening salivary proteins related to estrus, and to provide a reference for the development of kits/strips for estrus identification of sows. ABSTRACT: The estrus cycle of multiparous Large White sows was divided into three stages to solve the problems of heavy workload and low accuracy of the traditional estrus identification method in pig production. Saliva protein was extracted from the oral saliva of multiparous sows. Label-free quantitative proteomics was used to detect salivary proteome, and MaxQuant software was used for quality control. Results showed that 246 proteins were identified in the three stages, where 40 proteins were significantly different (p < 0.05). The total proteins identified were enriched by STEM software and the protein function was annotated by using the ClueGO plug-in in the Cytoscape software. The results were enriched to eight different trends. The annotated items were related to protein synthesis and processing and estrogen response. Gene ontology and the Kyoto Encyclopedia of Genes and Genomes enrichment analysis of differential proteins involved in the pathways and entries included oocyte meiosis, response to estradiol, and oogenesis. Further interaction analysis showed that an interaction occurred between P00355, F1SHL9, P28491, F1SDR7, F2Z558, F1RYY6, and F2Z5G3 proteins. The findings served as a basis for revealing the changes in salivary protein content in the sow estrus cycle and provided a reference for the development of an estrus identification kit/test strip in the next step.