Postpartum health disorders in lactating dairy cows and its associations with reproductive responses and pregnancy status after first timed-AI.

The objective was to evaluate the association between postpartum health disorders, reproductive responses and pregnancy status in lactating multiparous cyclic Holstein cows. Cows were retrospectively categorized as healthy (n = 70) or sick (n = 60) based on postpartum health records and serum metabolites. Sick cows were further categorized as having metabolic (MET; n = 35), infectious (INF; n = 15), or both diseases (MET/INF; n = 10). Blood samples were collected on d 7 and 14 after calving to determine serum concentrations non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB) and aspartate aminotransferase (AST), on d 0 (TAI), 8, 16, 18 and 20 after TAI to determine concentrations of progesterone (P4; d 0, 8, 16, 18 and 20) and prostaglandin F metabolite (PGFM; d 16, 18 and 20) and interferon-stimulated gene-15 (ISG15; d 16) relative mRNA expression. Cyclicity was determined by transrectal ultrasonography 30 d postpartum and cows were subjected to a GnRH-based TAI protocol (to classify cows bearing a visible CL as cyclic). Prediction of pregnancy status on d 16 after TAI was determined by ISG15 mRNA gene expression relative to β actin and following, pregnancy was diagnosed by transrectal ultrasonography at 32 and 60 d after TAI. An interaction (P = 0.04) between occurrence of disease and pregnancy status was detected for the expression of ISG15 in blood, with healthy pregnant healthy cows having the greatest relative expression of ISG15. Postpartum health disorders were associated with reduced concentration (P < 0.05) of serum P4 post TAI. However, serum P4 concentrations at TAI were greater (P = 0.01) in sick cows (0.65 ± 0.09, 0.86 ± 0.13 and 0.75 ± 0.10 ng/mL for MET, INF and MET/INF cows, respectively) compared with that in healthy cows (0.24 ± 0.10 ng/mL). Serum concentrations of PGFM after TAI was reduced in healthy cows, regardless of pregnancy status. Pregnancy status on d 16 after TAI predicted by ISG15 mRNA expression and P/AI on d 32 and 60 after TAI based on ultrasonography, were negatively affected (P < 0.05) by occurrence of health disorders. Similarly, pregnancy loss from d 16 to 32 and d 16 to 60 after TAI was greater (P < 0.05) in sick cows compared to that in healthy cows. However, neither P/AI nor pregnancy loss were associated to the category of postpartum health disorder. Cows affected by postpartum health disorders had overall reduced P4 and greater PGFM serum concentrations after TAI, which were associated with reduced pregnancy success and enhanced pregnancy loss. Collectively, our findings support the hypothesis of a carryover effect of disease on reproductive responses, embryo survival and maintenance of pregnancy in lactating dairy cows independent of the category of postpartum health disorder.