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Risk factors for early pregnancy loss in primiparous Holstein cows.

P. Pinedo



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Risk factors for early pregnancy loss in primiparous Holstein cows.
E. Webster1, D. Manriquez1, P. Melendez2, P. Pinedo*1. 1Colorado State University Fort Collins, CO, 2University of Georgia Tifton, GA.

The objective was to identify risk factors associated with early pregnancy loss (EPL) in primiparous Holstein cows in one herd in Colorado. Cows were maintained in a cross-ventilated barn, milked 3�, and subject to AI at about 80 DIM, following a double OvSynch protocol. Data included 5,176 pregnancies in cows conceiving between January 2017 and October 2019. Risk factors considered were: number of inseminations as a heifer (SCH; 1;2; ≥ 3), age at first calving (AFC), calving season (CS), average milk yield up to 100DIM (MY100), number of AI at conception (nAI; 1; 2—3; ≥ 4), season of conception (SCN), and DIM at conception. Pregnancy diagnosis was performed by ultrasonography (US) on d 33 � 3 after AI and reconfirmed at d 52 � 3 of gestation. EPL was defined as a positive pregnancy diagnosis at first US followed by a negative diagnosis at reconfirmation. Continuous data were analyzed by ANOVA and binary data by logistic regression. Average (95% CI) EPL was 10.2% (9.21—10.9%). The odds (95% CI) of EPL were 4.46 (2.95—6.76) and 2.70 (2.13—3.42) times greater for SCH ≥ 3 category than for SCH 1 and 2, respectively. The odds of EPL were 1.50 (1.18—1.92) times greater for fall than for winter calvings. Number of breeding was strongly associated with EPL: The odds of EPL were 52 (31—83) and 2.70 (2.19—3.24) times greater for nAI ≥ 4 category than for nAI 1 and nAI 2—3, respectively. The odds of EPL were 1.63 (1.27—2.09); 1.59 (1.21—2.09); and 1.44 (1.14—1.83) times greater for cows conceiving in spring, summer, and fall than for cows conceiving in winter, respectively. The average (SE) DIM at conception in cows having EPL was 121.8 (2.52) d vs. 115.9 (0.85) d in cows that remained pregnant (P < 0.01). No significant associations between AFC or MY100 and EPL were determined. In conclusion, EPL was associated with multiple risk factors including SCH, CS, SCN, and DIM at conception. A strong effect was established for nAI, especially for nAI ≥ 4.

Keywords: embryo, mortality, risk.