Effect of recombinant bovine somatotropin (rbST) treatment on follicular population and development in non-lactating dairy cows
Abstract
This study aimed to assess the long-term effects of recombinant bovine somatotropin (rbST) on follicle population and ovulatory follicle development in non-lactating dairy cows. Twenty-one Jersey cows were assigned to either the rbST (n=11) or control (n=10) group. On day -60, cows in the rbST group received a 500 mg subcutaneous injection of somatotropin (Lactotropin®, Elanco). On day 0, all cows received an intravaginal progesterone-releasing device (1.9 g, CIDR®, Zoetis) and a GnRH injection (100 mg, IM, Factrel®, Zoetis). On day 8, PGF2α (25 mg, IM, Lutalyse®, Zoetis) was administered, and the CIDR® device was removed. Twelve hours later, serum, follicular fluid, and granulosa cell samples were collected to analyze estradiol (E2) and progesterone (P4) concentrations. Total RNA from granulosa cells was extracted to assess gene expression of LHCGR, STAR, HSD-3B1, CYP11A1, CYP19A1, CYP17A1, IGFR, and PAPPA via real-time PCR. Antral follicle count was determined through ultrasonography on days -60, -53, -46, -14, -7, 0, and 8. Data were analyzed using repeated measures ANOVA and t-tests.
Results showed that rbST treatment had no significant effect on follicle count over the 60-day period, nor on serum and follicular E2 or follicular P4 levels at follicle aspiration. However, rbST treatment reduced PAPPA (P = 0.006), CYP11A1 (P = 0.04), and CYP19A1 (P = 0.002) mRNA expression in granulosa cells of the pre-ovulatory follicle. In conclusion, while a single dose of rbST did not impact antral follicle population or hormone concentrations, it decreased the expression of Opevesostat key steroidogenesis-related genes in granulosa cells of the pre-ovulatory follicle in non-lactating dairy cows.