Short communication: Plasma progesterone concentration and ovarian dynamics of lactating Jersey cows treated with 1 or 2 intravaginal progesterone inserts

The objectives of the current experiment were to determine circulating progesterone concentrations and ovarian follicle development of lactating Jersey cows treated with 1 or 2 controlled internal drug release (CIDR) insert containing 1.38 g of progesterone during proestrus. Cows were enrolled in the experiment at 34 ± 3 d in milk and were paired by parity, body condition score, body weight, and milk yield. Estrous cycles were presynchronized with an injection of GnRH concurrent with a new CIDR insert (study d −7) and 2 injections of PGF2α given 5 and 6 d after the GnRH injection (study d −2 and −1, respectively). Cows assigned to the 1CIDR treatment (n = 30) or 2CIDR treatment (n = 30) received 1 and 2 CIDR inserts, respectively, from study d 0 through 7. Control cows (n = 10) did not receive further treatment. On study d −2 and daily from study d 0 through 7, ovaries were examined by transrectal ultrasound and blood samples were collected for determination of progesterone. On study d 7, CIDR inserts were removed after ultrasound exam and blood sample collection. Progesterone concentration from study d 0 through 7 was greatest for 2CIDR cows (2.17 ± 0.09 ng/mL), followed by 1CIDR cows (1.37 ± 0.10 ng/mL) and control cows (0.62 ± 0.21 ng/mL). The interaction between treatment and study day affected progesterone concentration from study d 0 through 7. The average increase in progesterone concentration from study d 1 through 7 was 0.80 ng/mL for 1CIDR and 1.72 ng/mL for 2CIDR cows compared with control cows. The percentage of cows that ovulated between study d 0 and 7 was greatest for control cows (80%), but it did not differ between 1CIDR (12%) and 2CIDR (3.7%) cows. Growth of class III follicles (10-17 mm) identified on study d 0 was affected by treatment because 1CIDR cows had larger class III follicles than 2CIDR cows on study d 5, 6 and 7. A larger proportion of control cows developed a new follicular wave between study d 0 and 7 (control = 60.0%, 1CIDR = 12.0%, 2CIDR = 7.4%). Treatment of lactating Jersey cows with 1 and 2 CIDR inserts resulted in a 1 and 2 fold increase, respectively, in circulating progesterone concentration. Growth class III follicles from cows treated with 2 CIDR inserts was reduced compared with untreated cows and cows treated with 1 CIDR insert.