Progesterone concentrations before parturition in cows
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The objectives of this study were to evaluate the use of progesterone concentrations in predicting calving time in cows over 265 days of gestation. The incidence of retained fetal membranes after induction to parturition is evaluated as well. Data were collected from the online electronic patient files at the clinic of the Department of Farm Animal Health of the Faculty of Veterinary Medicine in Utrecht. Information was collected about progesterone concentrations, date of insemination, induction and C-section or spontaneous parturition, induction medications used, clinical signs prior to parturition and retained fetal membranes. P4 levels were checked every Monday, Wednesday and Friday from ± 265 days of pregnancy until parturition. The cows were induced to parturition using dexamethasone, and in approximately 50% of the cases prostaglandin was given as well, administered 12 hours after dexamethasone. The incidence of retained placenta was affected by three factors: C-section (P < 0,01), gestation length (P < 0,05) and induction treatment (P < 0,01). The independent effect of a C-section had the greatest influence, but induction was highly associated as well. Progesterone concentrations of non-induced cows were on Day 1 before parturition significantly lower (1,14 ng/mL; P < 0,01) than those of induced cows. On Day 0, on the other hand, there is no significant difference. Progesterone concentrations of both groups end around the same average concentration (1,0 ng/mL ± 0,17 [Mean ± SEM]). To analyze the influence of several variables on normal progesterone concentrations, only cows at full-term gestation were used. A significant correlation was calculated between progesterone concentrations and Days 0–7 before parturition (P < 0,05). From 8 days before parturition and further, no significant relationship is seen. Progesterone concentrations decline markedly within 2 days of parturition (Est. –4,58; P < 0,01). For each cow and each interval in days before parturition, the average decrease or increase in progesterone concentrations was calculated, in absolute numbers (ng/mL) and in percentages, as well as the 95% confidence interval and 95% reference interval. The dispersion in progesterone concentrations and decrease/increase was very high, with a lot of overlap for each interval. Based on the mean progesterone concentrations and the average decrease and increase in progesterone concentrations (all with 95% reference interval), progesterone concentrations were found to not be a useful means to predict calving time in cattle, because of the high dispersion in concentrations.