Abstract
Background:
Bull fertility is a critical determinant of success in an artificial insemination (AI) center. Fertility is strongly influenced by proteins present in seminal plasma and spermatozoa. Proteomics is an advanced analytical approach for identifying and characterizing these proteins and their associations with sperm fertility.

Aim:
This study aimed to identify and characterize the proteomic profiles of seminal plasma and spermatozoa derived from Indonesian-bred Simmental bulls and to compare them with imported Simmental bulls housed at the same AI facility.

Methods:
Semen samples were collected from three Indonesian-bred (S-Ind) and three imported (S-Imp) Simmental bulls using an artificial vagina. Seminal plasma and sperm pellets were separated and analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis following protein extraction and 1D SDS-PAGE separation. Protein identification was performed using Proteome Discoverer 2.2 software with Uniprot protein database. Gene Ontology and STRING analyses were conducted to assess protein functions and interactions.

Results:
LC-MS/MS analysis identified 68 and 92 proteins in seminal plasma and spermatozoa, respectively. Four proteins were unique to the S-Ind group in seminal plasma, while six proteins were unique to the S-Imp group. In spermatozoa, seven proteins were identified exclusively in the S-Ind group, whereas three proteins were detected only in the S-Imp group. The identified proteins were involved in spermatogenesis, sperm motility, capacitation, the acrosome reaction, fertilization, oxidative stress balance, and energy metabolism.

Conclusion:
The proteomic landscape and key biological functions of proteins in seminal plasma and spermatozoa from bulls bred in Indonesia were comparable to those observed in imported bulls.
These proteins are involved in spermatogenesis, sperm capacitation, the acrosome reaction, fertilization, energy metabolism, and sperm protection against oxidative stress.
Despite this overall similarity, distinct differences in protein composition and abundance were observed. S-Ind exhibited a higher abundance of proteins involved in metabolism and cellular protection, whereas S-Imp exhibited a greater abundance of structural proteins associated with sperm function.

Key words: Fertility; Proteomics; Seminal plasma; Simmental bulls; Spermatozoa.