Thangavelu, G., Gobikrushanth, M., Colazo, M. G. and Ambrose, D. J. 2015. Pregnancy per artificial insemination and pregnancy loss in lactating dairy cows of a single herd following timed artificial insemination or insemination at detected estrus. Can. J. Anim. Sci. 95: 383-388. The objective of this retrospective study was to determine the factors affecting pregnancy per artificial insemination (P/AI) and pregnancy loss in lactating dairy cattle. Breeding records (n=1466) for 5 consecutive years were evaluated from one dairy herd. The effects of type of breeding [timed artificial insemination (TAI; n=1246) vs. insemination at detected estrus (IDE; n=220)], parity (primiparous vs. multiparous), body condition score (BCS; low =2.5 vs. high >2.5), year, season (summer vs. other seasons) and fertility group (high fertile <3 vs. low fertile ≥3 inseminations), on P/AI and pregnancy loss (i.e., late embryonic/early fetal loss, abortion and stillbirth) were determined using the GLIMMIX procedures of SAS software. Pregnancy per AI was influenced by type of breeding and season. Pregnancy per AI was lower (P<0.05) in cows that were TAI (28.7%) than IDE (37.1%) and during summer (30.3%) than other seasons of the year (35.5%). Pregnancy loss was higher (P<0.05) in low BCS (9.1%) than in high BCS (1.9%) cows. However, parity, year, and fertility group affected neither P/AI nor pregnancy loss.