The objective of this study was to evaluate the occurrence of pregnancy loss in dairy cattle using different pregnancy
biomarkers. The study was conducted in two commercial dairy farms. Holstein cows (n=140) and heifers (n=32) were
subjected to a hormonal synchronization protocol and TAI (D0). At D21 post-TAI, blood samples were collected for peripheral
blood mononuclear cells (PBMC) isolation and for assay of plasma progesterone by radioimmunoassay kit (MP Biomedicals),
and corpus luteum (CL) blood perfusion was evaluated by Doppler ultrasonography. An active CL was considered when
the blood perfusion was >25% and progesterone concentrations were >1 ng/mL. Plasma samples collected on D25 were
assayed for pregnancy-associated glycoproteins (PAGs) using a commercial ELISA kit (Ruminant pregnancy test kit, IDEXX®
laboratories). The abundance of interferon-tau stimulated genes (ISG15 and RSAD2) in PBMC was determined by RT-qPCR
and normalized to GAPDH and PPIA. Confirmatory pregnancy diagnosis was performed on D32 and D60 days post-TAI by
B-mode ultrasonography. Statistical analyses were performed using Chi-Square of SPSS software. The pregnancy biomarkers
were used to categorize the females that have undergone late luteolysis (LL - Non-pregnant females at D32, but with an active
CL at D21, and considered non-pregnant by abundance of ISGs on D21 and PAG’s test on D25); early embryonic mortality
from 21 to 25d (EEM - Non-pregnant at D32, but with presence of an active CL and considered pregnant by ISG abundance
on D21, and non-pregnant by PAG’s test on D25); late embryonic mortality from 25 to 32d (LEM - Non-pregnant at D32, but
with presence of an active CL and considered pregnant by ISG abundance on D21 and PAG’s test on D25); and late pregnancy
loss from 32 to 60d (LPL - Pregnant at D32 but non-pregnant on D60). Cows were also evaluated if had previous postpartum
issues (metritis, repeat breeder [>3 inseminations], retained placenta, abortion or stillbirth). A lesser rate of LL was observed
in heifers (P=0.02) than cows (6% [2/32] vs. 26% [36/140]); however, no difference (P>0.1) was found for EEM (6% [2/32] vs.
9% [13/140]), LEM (11% [4/32] vs. 6% [9/140] and LPL (0% [0/32] vs. 6% [9/140]). The pregnancy rate on D60 did not differ
(P>0.1) in cows with postpartum issues (18% [15/84]) or not (27% [15/56]). Unhealthy cows had greater (P<0.05) rate of LEM
(11% [9/84] vs. 0% [0/56]) and lesser rate of LPL (2% [2/84] vs. 12% [7/56]), but no difference was observed for LL (25% [21/84]
vs. 27% [15/56]) and EEM (10% [8/84] vs. 9% [5/56]). In conclusion, lactating dairy cows had a greater occurrence of LL than
heifers, indicating a possible extension of CL life-spam without involving interferon-tau stimulus. Reproductive postpartum
issues affect the occurrence of pregnancy loss in dairy females, especially in the early stages of pregnancy.