Administration of progesterone to cows with ovarian follicular cysts results in a reduction in mean LH and LH pulse frequency and initiates ovulatoryfollicular growth

Cows with ovarian follicular cysts were treated with progesterone to determ ine whether a reduction in LH concentrations and initiation of ovulatory fo llicular waves would occur. Cysts were diagnosed using transrectal ultrason ography when single follicular structures > 20 mm or multiple structures > 15 mm in diameter were present for 7 d in the presence of low progesterone concentrations. Three groups were studied: 1) cows with normal estrous cycl es (CYC, n = 8); 2) cows with untreated cysts (CYST, n = 7); and 3) cows wi th cysts treated with two progesterone-releasing intravaginal devices (PRID , n = 8) for 9 d. Ovaries were examined with transrectal ultrasonography, a nd blood samples were collected daily for analysis of progesterone and FSH. Serial blood samples for determination of mean LH and LH pulse frequency w ere collected on d 0 (CYST and PRID cows only), 1, 5, 9, and 10. Progestero ne concentrations were higher in PRID cows than in CYST cows throughout the PRID treatment period (P < .002). On d 0, LH pulse frequency was similar ( P = .10) in PRID (6.6 +/- .6 pulses/8 h) and CYST cows (5.1 +/- .6 pulses/8 h), but mean LH tended to be higher (P = .054) on d 0 in PRID cows (2.5 +/ - .2 ng/mL) than in CYST cows (1.9 +/- .2 ng/mL). Mean LH and LH pulse freq uency decreased (P < .002) by d 1 in PRID cows (1.1 +/- .2 ng/mL, 1.8 +/- . 6 pulses/8 h) compared with CYST cows (2.1 +/- .2 ng/mL, 5.6 +/- .6 pulses/ 8 h) and remained lower throughout most of the experimental period. The FSH concentrations were higher (P < .01) in PRID cows than;in CYC and CYST cow s on d 3 and 4. The increase in FSH concentrations preceded emergence of th e PRID-induced follicular wave. All PRID cows and four of seven CYST cows i nitiated new follicular waves during the period of PRID treatment. Follicul ar waves were initiated later (P < .05) in CYST cows (d 5.2 +/- 1.7) and PR ID cows (d 5.5 +/- .6) than in CYC cows (d 1.8 +/- .3). Cysts were smaller (P < .01) at the end of the treatment period in PRID cows compared with CYS T cows. No CYST cows ovulated, but all PRID cows ovulated newly developed f ollicles 3 or 4 d after PRID removal. Treatment with exogenous progesterone reduced LH in cows with cysts, and this was followed by development of nor mal ovulatory follicles.