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Effect of double ovulation on corpus luteum blood perfusion, peripheral progesterone, and hepatic steroid inactivating enzymes in dairy cattle
Double ovulation is more common in Holstein cows than other dairy breeds. The effects of double ovulation on the corpus luteum (CL) and subsequent peripheral progesterone and clearance have not been examined. Thus, the objective of this experiment was to determine if induction of an accessory CL, via human chorionic gonadotropin (hCG), alters blood perfusion of CL, peripheral concentrations of progesterone, or hepatic steroid inactivating enzymes. Lactating, non-pregnant, Holstein cows (n = 19) were synchronized using Ovsynch. Seven d post-ovulation, 8 cows received an injection of hCG (1,000 IU, im) while 11 cows received no treatment. Size of CL were measured and photos of blood perfusion of CL were recorded (d 10 to d 18) via Doppler ultrasonography and a blood sample was collected daily. Picture images were analyzed visually by two consistent technicians, averaged, and categorized (0 to 9 with 0 = no perfusion and 9 = complete perfusion). Pictures were also assessed using ImageJ software for integrated density of pixels. On d 13 post-ovulation, a liver biopsy was performed and hepatic steroid inactivating enzymes were analyzed. The MIXED procedure of SAS was used with day as a repeated measure and cow as a random variable. LSMeans and pooled SEM are presented. Cows with 1 or 2 CL had similar (P = 0.62) peripheral concentrations of progesterone, 7.2 ± 0.7 and 7.7 ± 0.8 ng/mL, respectively. Compared to cows with 1 CL, cows with 2 CL had similar (P > 0.80) volume (7.3 ± 1.0 vs 7.7 ± 1.2 cm3) but greater (P < 0.001) total blood perfusion (3.8 ± 0.3 vs 6.9 ± 0.3 visual score; 4,403.7 ± 641.3 vs 7,781.8 ± 759.2 pixels). Both visual and pixel perfusion scores adjusted for CL volume (per cm3 of luteal tissue) were greater (P < 0.01) in cows with 2 CL than 1 CL with a day × treatment interaction. Hepatic enzyme (cytochrome P450 1A, 3A, and 2C, aldo-keto reductase 1C, and uridine diphosphate-glucuronosyltransferase) activities were not different (P > 0.23) between treatment groups. Overall, the increased blood perfusion of CL in cows with 2 CL did not correspond to peripheral concentrations of progesterone or clearance as measured by hepatic enzyme activity, perhaps indicating that a double ovulation does not impact progesterone necessary to maintain pregnancy.
Keywords:
blood perfusion, corpus luteum, progesterone