Decreased bull fertility: age-related changes in sperm motility and DNA fragmentation

Abstract

This study aimed to analyze the effect of the age of bulls on sperm motility and DNA fragmentation and its impact on fertility. Ninety-six frozen semen straw from eight bulls were divided into four groups based on age (group-1: 5-6 years; group-2: 7-8 years; group-3: 9-10 years; group-4: 11-12 years). Total and progressive motility were detected by using computer-assisted semen analysis (CASA), while DNA fragmentation was detected by Toluidine blue staining. Over 500 artificial insemination services in the field were used for fertility rate analysis. The results of the analysis of total motility, progressive, and DNA fragmentation in all age groups still meet the minimum standard for artificial insemination programs. Analysis of progressive motility and DNA fragmentation showed significant differences in each age group (P<0.01), whereas analysis of total motility showed no significant differences in group-2 (7-8 years) and group-3 (9-10 years) (P>0.01). Increased age in bulls correlated significantly with increased sperm DNA fragmentation (P<0.01), decreased total and progressive motility (P<0,01), and potentially reduced the fertility rate (P<0.01). In conclusion, although the quality of frozen semen still meets the standards for artificial insemination programs, the age factor in bulls needs to be considered for achieving maximum fertility.