Abstract
Background:
The genetic quality and productivity of Bali cattle can be improved by selecting superior bulls, and semen quality evaluation can support this selection. Physical and microscopic semen quality assessments alone are insufficient to fully describe spermatozoa functionality.

Aim:
This study aimed to evaluate the quality of fresh semen and analyze the spermatozoa protein profile and its correlation.

Methods:
Semen samples were collected from 9 Bali bulls aged between 4 and 12 years. Spermatozoa motility, spermatozoa concentration, viability, abnormality, plasma membrane integrity, and acrosome integrity were assessed. Protein spermatozoa concentration was determined using the bicinchoninic acid method, protein characterization was performed by 1D-SDS-PAGE, and MW was determined using a standard marker.

Results:
Most semen quality variables were significantly different (p < 0.05) among the Bali bulls, except for fast motility and viability (p > 0.05). The detection of spermatozoa protein bands differed between bulls. Exploratory Spearman correlation analysis revealed that motility and total protein bands were significantly correlated with protein concentration (p < 0.05). Total protein bands also show significant correlations (p < 0.05) with motility and abnormality.

Conclusion:
The quality of fresh semen and spermatozoa protein detection differ among Bali bulls. In addition, spermatozoa protein concentrations and protein bands were significantly correlated with fresh semen quality in Bali bulls, suggesting their preliminary potential as molecular indicators associated with fresh semen quality.

Key words: Acrosome integrity; Bali cattle; Protein band; SDS-PAGE; Semen quality.