Tests were applied to extended, chilled boar semen to further define those factors associated with return to estrus in inseminated female pigs (sows and gilts). Females were each inseminated twice with the same batch of extended chilled single-sire semen that was concurrently assessed at the Charles Sturt University Andrology Laboratory (CSUAL) in Australia. Semen traits tested were pH, clump score and temperature while sperm morphology assessment included abnormal heads, acrosomes, midpieces, tails and retained cytoplasmic droplets. Sperm motility and concentration were tested using a computerized sperm analyser (CASA) system. Female return types were categorised as early, early regular, early irregular, late regular and late. Depending on the type of variable of interest, statistical analyses used linear mixed models or generalised linear models. Terms included in the models were dam line, sire line, parity, insemination season, return type, individual boars and inseminators. Of 1205 inseminated females, 894 (74.2%) farrowed, 3 (0.2%) aborted and 308 (25.6%) showed different types of return to estrus. The fixed variables dam-line, sire-line and parity were significantly (P < 0.05, P < 0.05 and P < 0.001 respectively) associated with female return type, although inseminator and insemination season were not. Of the semen/sperm traits tested, the acrosomal defects that were significantly associated (P < 0.05) with female return-type were morphologically abnormal acrosomes and percent intact acrosomes while cytoplasmic droplets, normal morphology and bacterial score also influenced return type (P < 0.05). There were also correlations between sperm factors such as abnormal sperm tails, motility and velocity and sow parity. In conclusion, sperm morphologic assessment, in particular of the acrosome region, was useful in predicting female returns to estrus.