Summary. Two experiments were conducted to (1) investigate developmental endocrinology of ovarian follicular cysts (cysts) in cattle and (2) evaluate effects of cysts on hypothalamic and hypophysial characteristics. Cysts were induced with oestradiol-17β (15 mg) and progesterone (37·5 mg) dissolved in alcohol and injected s.c. twice daily for 7 days. Cysts were defined as the presence of follicular structures (which may or may not have been the same structure) of 2·0 cm in diameter or greater that were present for 10 days without ovulation and corpus luteum development.
In Exp. 1, 22 non-lactating, non-pregnant Holstein cows were allocated to 3 groups. Beginning on Day 5 (oestrus = Day 0) of the oestrous cycle, 7 cows (Controls) were treated with twice daily s.c. injections of ethanol (2 ml/injection) for 7 days. Luteolysis was then induced with PGF-2α and blood samples were collected daily every 15 min for 6 h from the morning after the PGF-2α injection (Day 13) until oestrus. Steroids to induce cysts were injected as previously described into the remaining cows (N = 15). Three blood samples were collected at 15-min intervals every 12 h throughout the experimental period. Additional blood samples were collected every 15 min for 6 h on a twice weekly basis. After steroid injections, follicular and luteal structures on ovaries were not detected via rectal palpation for a period of 36 ± 4 days (static phase). Then follicles developed which ovulated within 3–7 days (non-cystic; N = 7) or increased in size with follicular structures present for 10 days (cystic; N = 8). Mean (± s.e.m.) concentrations of LH, FSH, oestradiol-17β and progesterone in serum remained low and were not different during the static phase between cows that subsequently developed cysts or ovulated. During the follicular phase, mean serum concentration of LH (ng/ml) was higher (P < 0·1) in cows with cysts (2·9 ± 0·2) than in cows without cysts (1·1 ± 0·1) or control cows (1·4 ± 0·2). In addition, LH pulse frequency (pulses/6 h) and amplitude (ng/ml) were higher (P < 0·1) in cows with cysts (3·6 ± 0·3 and 2·2 ± 0·3, respectively) than in non-cystic (2·3 ± 0·2 and 1·0 ± 0·2, respectively) and control (1·8 ± 0·1 and 1·1 ± 0·2, respectively) groups during the follicular phase.
In Exp. 2, 20 non-lactating, non-pregnant dairy cows were used: 15 cows received exogenous steroids as previously described. Hypothalamic and hypophysial tissues were collected after diagnosis of cystic structures in 11 cows (cystic group). The remaining 4 cows in the steroid-treated group ovulated and were assigned to the control group in addition to 5 non-steroid treated cows. Hypothalamic and hypophysial tissues were collected during the late-luteal phase (Days 16–18) from these control cows (N = 9). Anterior pituitary concentrations (μg/g) of LH (60·5 ± 11·0, 44·6 ± 11·7), FSH (30·2 ± 4·0, 22·1 ± 4·6) and receptors for GnRH (17·2 ± 2·2, 23·4 ± 2·6 m × 10−10/mg protein) did not differ between cows with cysts and control cows, respectively. Content of GnRH (ng) in the combined preoptic area and hypothalamus proper was higher (P < 0·05) in control cows (37·7 ± 6·6) than cows with cysts (18·6 ± 6·1). In the pituitary stalk median eminence, GnRH content (ng) tended to be higher (P ≥ 0·1) in cows with cysts (38·5 ± 9·6) compared with control (21·1 ± 15·2) cows.
Secretory patterns (mean concentration, pulse frequency and amplitude) of LH were therefore increased during the follicular phase in cows which developed cysts compared to cows which subsequently ovulated. In addition, hypothalamic GnRH content, but not pituitary characteristics, appeared to be altered in cows with cysts.
Keywords: ovary; follicular cysts; dairy cattle; gonadotrophins; hypothalamus; pituitary