The aim of this study was to compare vaginal mucus scoring and ultrasonographic assessment of uterine content as predictors of future reproductive performance of dairy cows. Holstein-Friesian cows (n = 493) from seven commercial dairy farms were enrolled in this study. All cows received one prebreeding examination (PBE) between 21 and 38 days after parturition. During the PBE, vaginal mucus was scored (MS) and the transrectal ultrasonographic examination of the uterus to assess content (UTS) took place. The MS was scored on a scale of 0 to 3 using a Metricheck device and appearance of the uterus on transrectal ultrasound was scored on a scale of 0 to 4 based on the presence and consistency of intraluminal fluid. Other data collected from each cow included the farm ID (F_ID), conception rate to first service, length of breeding window, lactation number, calving month, body condition score (BCS) at calving, BCS loss after calving, BCS at PBE, days in milk at PBE, 305 day milk yield, economic breeding index (EBI), EBI fertility subindex and EBI health subindex. For each cow these parameters were analyzed using univariate Cox proportional hazard model to evaluate the effect of variables on the reproductive performance, measured as positive pregnancy status (PS) at the end of the breeding season. Receiver-operating characteristic analysis of the diagnostic tests compared with each other took place as well. Cows with positive UTS were 7.75 times more likely to have a positive MS as well (P < 0.01). The PS hazard ratios for cows with UTS0, 1, 2, 3, and 4 were 1; 0.84; 0.53; 0.78; 0.28, respectively (P < 0.001). For the cows with MS0, 1, 2, and 3, the PR hazard ratios were 1; 1.02; 0.51; 0.75; respectively (P = 0.01). Conception rate to first service, breeding window, and PS were significantly better for the cows with UTS0, 1 and 2 compared with the cows with UTS3-4 and MS2+3 (68%; 18%, [P = 0.020]; 29; 75 days, [P = 0.001]; 95%; 55%; [P = 0.010], respectively). There was a significant effect of days in milk at PBE in relation to the subsequent PS (P = 0.04). Cows in lactation number 5 or more were less likely (r = 0.69) to get in calf before the end of the breeding season than cows in their first lactation. Cows that calved later in the season were less likely to become pregnant before the end of the breeding season (P < 0.03). Younger cows (lactation <5) and cows with MS and UTS scores of 0 and -1 had significantly better reproductive performance (P < 0.04). Receiver-operating characteristic analysis showed that MS did not always reflect UTS, but cows with positive UTS were 7.75 times more likely to have a positive MS (P < 0.01) and a high UTS had a larger negative effect on time to PS than a high MS (P < 0.05). In conclusion, both prebreeding vaginal mucus evaluation with the Metricheck device and an ultrasound scan of the uterus serve as a good predictor of the subsequent PS. There is overlap between the two systems, but the best predictor for future reproductive outcome of the cow is a combination of both.
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