Fate of cystic ovarian follicles, clinical responses, and pregnancy in dairy cows subjected to Ovsynch and timed artificial insemination, with or without an intravaginal progesterone device

Our objectives were to determine the fate of cystic ovarian follicles (COF), clinical responses, and pregnancy to timed artificial insemination (TAI) in lactating Holstein cows subjected to an Ovsynch protocol, with or without insertion of a progesterone releasing intravaginal device (PRID). Cows diagnosed with at least 1 COF (≥ 25 mm) were given 100 µg of gonadorelin acetate (GnRH; day –10 and day –1), 500 µg cloprostenol (prostaglandin F2α; day –3), and TAI (day 0). Cows randomly received PRID® (n = 49) for 7 days or NO-PRID (n = 62). Transrectal ultrasonography was conducted on days –10, –3, 0, 1, and 11 to monitor ovarian responses and on day 32 for pregnancy diagnosis. Cows were also categorized as low progesterone (LP; n = 50) or high progesterone (HP; n = 61) based on plasma progesterone concentrations (< or ≥ 1.0 ng/ml) or luteal status (presence or absence of luteal tissue) on day –10. Mean (± SEM) diameter of COF was 33 ± 0.6 mm. Although ovarian responses did not differ by PRID treatment, a higher (p = 0.05) proportion of COF in HP compared to LP cows underwent complete luteinization (21 versus 8%) after 1st GnRH treatment. In contrast, the proportion of cows ovulating an existing follicle after 1st GnRH treatment was higher (p = 0.03) in LP than in HP cows (72 versus 54%). No interactions existed between treatment (PRID or NO-PRID) and progesterone categories (LP, HP) in any of the ovarian or endocrine responses. Furthermore, 10% of COF ovulated and 62% of other preexisting follicles ovulated after 1st GnRH treatment. A new follicle was detected (day –3) in 95% of cases and 84% ovulated after 2nd GnRH. Pregnancy per AI did not differ (p = 0.46) between PRID and NO-PRID cows (37 versus 45%). Plasma progesterone at TAI was elevated (p = 0.02) in LP than HP cows (0.7 versus 0.2 ng/ml) and pregnancy tended to be lower (p = 0.13) in LP than in HP cows (34 versus 48%). In summary, cows with COF responded normally to Ovsynch protocol; although incorporating PRID into the protocol was not beneficial, cows with HP status at the start of the protocol tended to have higher pregnancy per AI.