Abstract
Ovarian quiescence was diagnosed in 5 Holstein heifers by repeated rectal palpations. The heifers were injected intramuscularly with 100-400 μg of LH-RH analogue (LH-RH-A) i.e. [Des-Gly-NH2 10, Pro-ethylamid9]-LH-RH. When the treatment failed to induce the ovarian cyclic activity, a second or third treatment was conducted with the same or larger dosage of the hormone 21 or 41 days after the preceding treatment. A total of 10 cases were treated using 5 heifers. They were divided into divisions I to IV. Division I consisted of 3 cases each received a single injection of 100 μg of LH-RH-A. Division II consisted of 3 cases each received double injections of 100 μg at 1 h interval. Division III consisted of 3 cases each received a single 200 μg injection. Division IV was 1 case which received a single 400 μg injection. At the time of treatments heifers were 18.9±1.7 (Mean±SD) months in age and 328.2±14.0 kg in weight. Ovarian changes were traced by rectal palpation at inter-vals of 6 h to 2 days. Plasma progesterone (P) and estradiol-17 β (E2) concentrations were determined by radioimmunoassay using samples collected at 12-48 h intervals during the experimental period.
Results: 1. Ovulations were induced 37.5±5.3 (in a range of 30-48) h after LH-RH-A treatment in 8 cases (80.0%) in all, or 2, 2, 3 and 1 cases of divisions I, II, III and IV, respectively. Second ovulation occurred spontaneously 8-9 days after the induced ovulation in 3 out of 8 cases (or 1 case each of divisions II, III and IV). The normal ovarian function began in these 3 cases after the 2nd ovulation. Ovarian quiescence occurred again in the other 5 cases. In the remaining 2 cases of divi-sions I and II, no ovulation was induced and the ovaries remained quiescent. 2. Development of corpus luteum (CL) was observed in 7 of the 8 cases after the induced ovulation, although this induced CL was always subnormal in size and began to degenerate as early as 5-7 days after the ovulation. Plasma P concentration increased in 4 cases of these 7 showing small peaks (1.2-2.8 ng/ml) after the induced ovulation. This increase coincided with the development of the induced CL. In the other 3 cases, no P increase was seen after the ovulation. Neither development of CL nor increase of P was observed in the remaining case after the induced ovulation. 3. Follicles developed in each of the 7 cases before and during the period when the induced CL degenerated, and the follicles ovulated 8-9 days after the induced ovulation in 3 cases. In the other 4 cases they became atrophic and degenerated. Plasma E2 concentration increased in 4 cases of these 7 to reach obvious peaks (8.7-19.5 pg/ml). This increase coincided with development and maturation of the follicles. In the other 3 cases no increase of E2 was noted during the period of follicular development. 4. In all 3 cases in which following events were observed after the induced ovulation, second ovulation occurred and normal ovarian cyclic activity started subsequently; plasma P concentration reached small peak with development of the induced CL, plasma E2 concentration reached obvious peak with development and maturation of the follicle during the period of degeneration of the induced CL..
These results indicate that good ovarian responses to LH-RH-A treatment required at least 200 μg. It is also indicated that induced CL must be functional enough to form a small P peak in plasma, and follicle must reach maturity and secrete E2 activity in coincidence with the degeneration of the induced CL for LH-RH-A treatment to induce ovarian cyclic activity in ovarian quiescent heifer.
