Reproduction and genetic improvement in dairy cattle: Sustaining a critical link in the era of opportunities

Fertility and genetic improvement are fundamentally interdependent in dairy cattle breeding: reproductive success determines the realization of genetic gain, while selection decisions shape the genetic capacity for reproduction. Historically, fertility declined because breeding objectives prioritised milk production, trait definitions captured only a narrow portion of reproductive biology, heritability was suppressed by strong environmental influences, and phenotypic data were often incomplete or imprecise, a limitation that still affects fertility evaluations in many systems. Although genomic selection (GS) has reversed long-standing negative trends and enabled more balanced breeding goals, fertility traits still receive comparatively low emphasis in selection indices. This underrepresentation is further sustained by extensive reliance on management interventions—particularly hormonal synchronisation—that improve phenotypic fertility in the short term but risk obscuring genetic variation, biasing evaluations and conflicting with societal expectations for sustainable livestock systems. This review synthesises fertility within three complementary domains: the biological mechanisms underlying reproduction, the genetic architecture and evaluation systems used to improve it, and the management practices that shape the phenotypes on which selection depends. Across these domains, recent progress has been considerable. Genomic selection has increased the accuracy of breeding values for low-heritability traits, reproductive biotechnologies have intensified selection and shortened generation intervals, and emerging indicator traits, high-throughput phenotyping and richer genomic resources offer new opportunities to align fertility evaluations more closely with underlying biology. Developing evaluations for male fertility, meanwhile, represents an accessible additional avenue for strengthening genetic improvement. Looking ahead, genome editing and advanced reproductive interventions offer unprecedented potential to overcome genetic constraints, yet their practical use remains limited by current evaluation methodologies, the need for robust and biologically meaningful fertility phenotypes and societal acceptance of biotechnological innovation. Taken together, the evidence underscores that progress in fertility will depend not on individual technologies alone, but on maintaining alignment across the biological, genetic and management domains. Only when these dimensions operate synergistically—supported by coordinated strategies among key stakeholders including breeding organisations, AI companies, producers and laboratories—can selection act effectively on fertility, ensuring long-term reproductive resilience and the sustainability of dairy cattle breeding.