74 Relationship between the corpus luteum blood perfusion on 22 days after timed artificial insemination and pregnancy loss in precocious Nelore cows and heifers

The objective of the study was to evaluate the relationship between the corpus luteum (CL) blood perfusion (CLBP) in precocious heifers and cows with an active CL determined by Doppler ultrasonography at Day 22 after timed AI (TAI) and the false positive (FP) results and pregnancy losses (PL) in the confirmatory pregnancy diagnoses. We hypothesised that the FP rate and PL are negatively associated with CLBP in nulliparous and primiparous Nelore females. For this, a retrospective analysis was performed using data from 1720 heifers aged between 11 and 16 months and 923 primiparous cows aged 23 to 26 months (between 22 and 57 days postpartum) subjected to an oestradiol/progesterone-based TAI protocol initiated 10 days before TAI (Day −10; Day 0 = TAI). On Day 14 (cows) or 15 (heifers), females were submitted to an oestradiol/progesterone-based resynchronization protocol. On Day 22, all females were evaluated by transrectal Doppler ultrasonography (Z5, Mindray) to estimate the CLBP (subjective evaluation of colour signals on a scale of 0–100%, 5 points between degrees). The data of CLBP from 64 heifers and 19 cows was not recorded. Only animals with CLBP ≤25% continued in the resynchronization protocol and were inseminated 48 h later. Cows with an active CL (≥30% of CLBP) were submitted to a confirmatory pregnancy diagnosis (PD) based on the identification of an embryo or fetus with heartbeats on Days 29–37 (PD1), 56–62 (PD2), and 94–146 (PD3). The rate of FP between Day 22 and PD1, and PL between PD1 and PD2 (early-PL) and PD2 and PD3 (late-PL) were calculated. A receiver operating characteristic (ROC) analysis was performed to determine a cutoff point for classifying the CLBP in low (≤40%; n = 234 heifers and 159 cows) or high (>40%; n = 297 heifers and 321 cows). The FP and PL rates were analysed by the PROC GLIMMIX considering the main effect of CLBP class, parity order, and their interaction or by PROC LOGISTIC of SAS software. The rate of active CL at the Doppler diagnosis was 34.6% (595/1720) for heifers and 54.3% (501/923) for cows. For animals with an active CL, a CLBF class by parity order interaction was not observed for any variable. Females with low CLBP compared to high CLBP had greater FP rate (22.4% (88/393) vs 6.9% (43/618)) and late-PL (10.3% (29/282) vs 6.8% (35/517)). Heifers compared to cows had a greater FP rate (16% (85/531) vs 9.6% (46/480)) and late-PL (12% (49/409) vs 3.6% (15/411)). The early-PL rate (total: 6.5% (57/878)) was not affected by any factor. The ROC curve indicated that the CLBP was a significant (P < 0.05) predictor of the FP rate and PL for heifers and cows. Logistic regression analysis indicated a linear or quadratic negative relationship (P < 0.05) between the CLBP and the probability of an FP and late-PL results. In conclusion, cows with a CLBP ≤40% determined by Doppler imaging on Day 22 are more likely to be identified as an FP in the confirmatory diagnosis of pregnancy and to experience a late PL. Also, the rates of FP results and late PL are greater in precocious Nelore heifers than in primiparous cows.

This work was funded by FAPESP (2017/18937–0; 2022/14936–7).