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Carryover effects of postpartum diseases on early conceptus development in dairy cows
Postpartum diseases constitute one of the major problems affecting fertility in dairy cows. The objective was to investigate the carryover effects of postpartum clinical diseases on early embryo development. From calving to first artificial insemination (AI), prevalence of calving problems, metritis, mastitis, lameness, digestive and respiratory problems were recorded for a group of 617 dairy cows. Cows had estrous cycle synchronized and were subjected to induced ovulation and timed AI. A total of 419 cows had their uterus flushed on day 6 after AI and the structures recovered were evaluated for fertilization and embryo quality. The remaining 198 cows had their uterus flushed on day 15 after AI and interferon-tau (IFN-τ) concentration in fluid was measured and the recovered conceptuses were evaluated for size and morphology. A subsample of conceptuses (n = 22) had mRNA extracted and subjected to transcriptome analysis using Affymetrix Gene Chip® Bovine Array. The experimental design was considered a prospective cohort study with 2 independent groups (healthy vs. disease). Continuous variables were analyzed by ANOVA and binary data by logistic regression using the GLIMMIX procedure of SAS and fitting adequate data distribution. Microarray data were analyzed using Bioconductor software in R environment. Data were preprocessed using Gene Chip Robust Multi-Array function. Limma package was used to fit a linear model and adjust variances by empirical Bayes adjustment. Moderate t-test was performed for all pairwise comparisons and P values were adjusted for multiple testing using the Benjamini and Hochberg false discovery rate. Adjusted P < 0.05 and fold change > 1.5 characterized significant differences. Functional analyses were performed using Ingenuity Pathway Analysis. Cows that had at least one clinical disease from calving to first AI had reduced fertilization, smaller proportion of good quality embryos on day 6, smaller size of conceptus and smaller concentration of IFN-τ on day 15 compared to cows that did not have clinical diseases. Controlling for size of the conceptuses, transcriptome analysis resulted in 41 transcripts that were differently expressed. The gene with the greatest difference in expression was FAT/CD36, which is important for cell signaling during conceptus elongation. FAT/CD36 was downregulated in conceptus recovered from cows that had diseases compared to those recovered from cows that did not have diseases. In conclusion, clinical diseases prior insemination were associated with reduced fertilization and compromised early embryo development.
Keywords: embryo, dairy cow, disease