Effects of induction of low plasma progesterone concentrations with a progesterone-releasing intravaginal device on follicular turnover and fertility in cattle

Abstract

The effects of concentration of progesterone in plasma on development and fertility of the first wave dominant follicle were studied in cattle. To identify a source of exogenous progesterone that would permit extension of the first wave dominant follicle, nonlactating Holstein cows (n = 6) received on day 8 of two successive oestrous cycles an injection of PGF(2α) (25 mg) and a new (1.9 g of progesterone (Period 1)) or used (≃ 1.2 g of progesterone (Period 2)) CIDR-B device that was removed on day 17. Control cows (n = 6) received a new CIDR-B device on day 8 that was removed on day 17 and a PGF(2α) injection (25 mg) on day 17. Ultrasonography and collection of blood samples were performed on alternate days throughout the experiment. Plasma concentrations of progesterone and oestradiol were different between treatments (P < 0.0001 and P < 0.05, respectively). The dominant follicle was maintained until day 17 and ovulated upon removal of the intravaginal device in 1 of 6, 6 of 6 and 0 of 6 in new CIDR-B, used CIDR-B and control groups, respectively (P < 0.01). The preovulatory dominant follicles were 14.2 ± 1.6 mm, 20 ± 1.3 mm and 10 ± 1.3 mm, respectively (P < 0.001) on day 17. There were fewer 5-9 mm follicles in cows having a persistent dominant follicle (P < 0.01). The interval to onset of oestrus was negatively correlated with size of the dominant follicle on day 17 (P < 0.001). In Expt 2, the fertility of oocytes ovulated from new (PGF(2α) on day 7; T1; n = 91) and persistent dominant follicles (PGF(2α) on day 7 and a used CIDR-B device inserted on day 7 and withdrawn on day 16; T2; n = 91) was tested using Holstein heifers. Size of the dominant follicle and plasma concentrations of progesterone and oestradiol on days 7 (T1) and 16 (T2) were different between treatments: 11.3 ± 0.2 versus 16.2 ± 0.3 mm (P < 0.001); 4.2 ± 0.2 versus 2.9 ± 0.3 ng ml-1 (P < 0.01) and 3.5 ± 0.3 versus 11.7 ± 1.7 pg ml-1 (p < 0.01), respectively. Pregnancy rates at first artificial insemination were 64.8% (46 of 71) and 37.1% (26 of 70) for new and persistent dominant follicles, respectively (P < 0.01). Pregnancy rates at second service were 50% and 52.8%, respectively. Low plasma concentrations of progesterone, therefore, resulted in persistency of the dominant follicle and temporarily impaired fertility.