Abstract
The aim of this study was to evaluate 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 allocated in rbST (n=11) or control (n=10) groups. On day -60, cows in rbST group received 500 mg of somatotropin (s.c. Lactotropin®, Elanco). On day 0, control and rbST cows received an intravaginal progesterone-releasing device (1.9 g, CIDR®, Zoetis) and GnRH (100 mg, IM, Factrel®, Zoetis). On day 8, cows received PGF2α (25 mg, IM, Lutalyse®, Zoetis) and the CIDR® was removed. Twelve hours after device removal (D8), serum, follicular fluid and granulosa cells samples were collected. Serum and follicular concentration of estradiol (E2) and progesterone (P4) were analyzed. Total RNA was extracted from granulosa cells to measure gene expression of LHCGR, STAR, HSD-3B1, CYP11A1, CYP19A1, CYP17A1, IGFR and PAPPA by real-time PCR. Ultrasonography was performed on days -60, -53, -46, -14, -7, 0 and 8 for antral follicle count. Results were analyzed by repeated measures ANOVA and t-test. There was no effect of rbST treatment on the number of follicles during the 60 days period, as well as no effect on serum and follicular fluid E2 and follicular fluid P4 at the moment of follicle aspiration. There was a reduction in PAPPA (P = 0.006), CYP11A1 (P = 0.04) and CYP19A1 (P = 0.002) mRNA levels in granulosa cells of the pre-ovulatory follicle of rbST treated cows. In conclusion, a single dose of rbST did not have long-term effects on antral follicle population, serum and follicular E2/P4 concentrations in non-lactating dairy cows. Despite that, rbST injection decreased granulosa cell expression of genes related to steroidogenesis in the pre-ovulatory follicle.
Highlights
Over the past years, aiming to improve the reproductive efficiency of dairy cattle, several strategies involving mainly nutrition management (Roche, 2006)Treatment with exogenous recombinant bovine somatotropin is usually performed during the postpartum period, aiming to enhance efficiency of milk synthesis (Bauman, 1999) and improve persistence of lactation (Bauman, 1992)
Follicles were classified by size and there was no effect of recombinant bovine somatotropin (rbST) treatment on Class 1 (9 mm; control: 1.09 ± 0.08 and bST: 1.02 ± 0.12 follicles; P = 0.92, Table 2)
There was a reduction in gene expression of steroidogenic enzymes in granulosa cells from pre-ovulatory follicles after the end of the treatment
Summary
Treatment with exogenous recombinant bovine somatotropin (rbST) is usually performed during the postpartum period, aiming to enhance efficiency of milk synthesis (Bauman, 1999) and improve persistence of lactation (Bauman, 1992). Despite positive effects on lactation, some studies suggest that rbST negatively affects reproductive performance in dairy cows in the long term (Cole et al, 1992; Kirby et al, 1997b; Santos et al, 2004). Rincón et al Effect of rbST on follicle development postpartum dominant follicle (Acosta et al, 2017). These results suggest a long-term effect of rbST on ovarian function depending in what stage of lactation is used that is still not totally understood
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