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Prepartum somatotropin administration affects IGF-I and NEFA concentrations in serum and follicular fluid of first postpartum dominant follicle in Holstein heifers
The aim of this study was to determine the effects of prepartum somatotropin administration on IGF-I and NEFA concentrations in serum and follicular fluid from the first postpartum dominant follicle of dairy heifers. Forty-nine late pregnant Holstein heifers were used from a commercial dairy herd in southern Brazil. Heifers were randomly assigned to two treatments: somatotropin (ST; n = 29), cows received two doses of somatotropin (500 mg/dose) at -28 and -14 days relative to calving; and Control (CN; n = 30); cows did not receive somatotropin application. Follicular development was monitored via ultrasound every 3 days starting at 8 DIM until the day in which the first dominant follicle reached a diameter of 16 mm. Follicular fluid from each cow (ST; n = 9 and CN; n = 9) was aspirated by ultrasound-guided transvaginal follicular aspiration. Blood samples were collected weekly since -28 from expected calving to 28 ± 2 DIM via venipuncture of the coccygeal vein in one tube without anticoagulant. Serum and follicular fluid NEFA concentration was determined with a commercially available enzymatic-colorimetric kit and IGF-1 concentrations were determined using a competitive, liquid-liquid phase, double-antibody IGF-1 radioimmunoassay procedure. Serum IGF-I concentration prepartum was affected by day (P < 0.0001), treatment (P = 0.016), and the interaction of day by treatment (P = 0.0005). Serum concentration of IGF-I was higher (P < 0.0002) at day -7 relative to calving. Also, serum IGF-I concentration prepartum was higher (P < 0.05) for ST (112.78 ± 3.95 mg/mL) than CN (97.37 ± 4.61mg/mL). There was a day effect (P < 0.0001) for serum IGF-I concentrations postpartum. For NEFA serum concentrations prepartum there was an effect of day (P = 0.006) and interaction of day by treatment (P = 0.0001) but no effect of treatment (P = 0.1185). There was an effect of the day (P < 0.0005) for serum NEFA concentrations postpartum. Follicular fluid IGF-I concentrations of the first postpartum dominant follicle was different (P = 0.0557) between ST (87.09 ± 7.73 mg/mL) and CN (64.26 ± 7.73 mg/mL). Follicular fluid NEFA concentration of the first postpartum dominant follicle was not different (P = 0.6897) between ST (0.71 ± 0.30 mEq/L) and CN (0.86 ± 0.33 mEq/L). In conclusion, prepartum injection of somatotropin in Holstein heifers increased serum IGF-I concentration prepartum and in follicular fluid of the first postpartum dominant follicle, potentially increasing the chance of ovulation in this class of follicles.
Keywords: dairy heifers, follicle, somatotropin, IGF-I.