Abstract
Background:
Artificial insemination (AI) improves genetic progress and reproductive efficiency in dairy cattle, but conception is influenced by semen quality, bull genetics, insemination timing, and management conditions. Cryopreservation may also impair sperm quality.

Aim:
This study evaluated semen quality and its changes during dilution and cryopreservation, characteristics of recorded bull genetic groups, and field-level factors associated with first-service conception rate (FSCR) in dairy cattle in northern Bangladesh.

Methods:
A total of 868 ejaculates from 30 clinically healthy AI bulls representing four recorded genetic groups were evaluated for sperm motility, viability, and morphology. Field fertility data were obtained from 942 dairy cows inseminated in 10 districts. Repeated-measures analysis was performed to evaluate semen quality among processing stages, and chi-square tests were performed to evaluate categorical associations. Multivariable binary logistic regression identified factors associated with conception, with adjusted odds ratios (AORs) and 95% confidence intervals (CIs). Laboratory semen quality and field fertility were analyzed as complementary components because individual inseminations were not consistently traceable to specific ejaculates or semen straws.

Results:
Short-term dilution did not significantly affect sperm motility or viability, whereas cryopreservation reduced motility (89.8% to 44.4%) and viability (94.3% to 67.3%; P < 0.001). Post-thaw motility remained stable during storage, while viability declined significantly during the early post-thaw period. Overall FSCR was 66.45%. Insemination >18 h after estrus detection was associated with higher conception odds than the 12–18 h reference interval (AOR = 22.73, 95% CI: 13.98–36.97; P < 0.001). Sperm motility was positively associated with conception (AOR = 1.13), and viability was inversely associated with conception (AOR = 0.88). The SL-75% group was more likely to conceive than SL-87.5% (AOR = 8.49). The odds of conception were also higher in Bogura, Kurigram and Panchagar than Rangpur.

Conclusion:
First-service conception was associated with AI timing, sperm motility, bull genetic group and district whereas cryopreservation decreased sperm quality. Enhanced AI timing, semen quality, and bull selection may enhance fertility but findings need to be interpreted with caution due to limited association between laboratory semen data and individual inseminations.

Key words: Artificial insemination; Bangladesh; Cryopreservation; First-service conception rate; Sperm quality.