The fertility gap between sex-sorted and conventional bovine semen: A systematic review and meta-analysis.

Sex-sorted semen is widely used in dairy cattle breeding, but reduced fertility compared with conventional semen remains an important limitation. This systematic review and meta-analysis updated evidence on fertility outcomes after artificial insemination (AI) with sex-sorted versus conventional semen in dairy cattle. PubMed, Web of Science Core Collection, and CAB Abstracts were searched on May 15, 2026. The searches identified 933 records; after removal of 407 duplicates, 526 unique records were screened. The quantitative synthesis included 41 reports contributing 47 eligible comparison rows (N = 1,440,625). In a report-clustered multilevel random-effects meta-analysis of crude event counts, AI with sex-sorted semen was associated with lower fertility than AI with conventional semen (RR = 0.764, 95% CI = 0.723-0.807; 95% prediction interval = 0.574-1.017; P < 0.001); estimated variance components were 0.01879 at the report level and 0.000505 at the comparison-row level. A one-report-one-estimate sensitivity analysis produced a similar estimate (RR = 0.764, 95% CI = 0.709-0.822). Excluding 16 non-randomized reports judged at serious risk of bias also yielded a similar pooled association (RR = 0.757, 95% CI = 0.699-0.820). Narrative evidence suggested several potential modifiers, including semen processing, sperm dose and state, AI timing, bull and herd effects, and female reproductive status, but these factors were supported to different degrees and should not be interpreted as established causal modifiers.