Relationship of Reproductive Behavior, Serum Luteinizing Hormone and Time of Ovulation in the Bitch

Open Access
Publisher Website
Google Scholar
Abstract
This study was performed to define the relationship betweed luteinizing hormone (LH), reproductive behavior and time of ovulation in the domestic bitch. Laparoscopy was effective for distinguishing ovarian follicular development and the morphological alterations indicative of ovulation and corpus tuteum (CL) formation. The actual moment of follicular rupture was observed in 2 animals. An LH surge was detected in all animals and mean LH values did not differ between bitches subjected to laparoscopy at 48 h intervals and those bitches which did not undergo laparoscopy during the experiment. During the proestrous-estrous period, baseline LH concentrations before and after the LH surge averaged 1.7 ± 0.1 ng/ml (S.E.). The major preovulatory LH surge ranged from 11.0–90.3 ng/ml with an average of 45.1 ± 4.4 ng/ml (S.E.) The duration of the LH surge was prolonged and occurred over a 3.5–4 day period. In 52% of the cycles examined, an episodic burst of LH (mean 6.1 ± 0.9 ng/ml) was detected 3–9.5 days prior to peak preovulatory concentrations of LH. This early release of gonadotropin may be associated with preovulatory luteinization and early progesterone secretion by the follicle. Evidence of ovulation was found in 93.5% of the follicles by 96 h after the LH peak, with the greatest incidence (77.2%) of follicular rupture occurring over the interval of 24–72 h following the LH peak. Wide variations in the physical and behavioral signs of estrus were observed. The mean length of proestrus was 8.7 days (range 3–17 days) and the mean duration of estrus was 11.4 days (range 3–21 days). The LH peak or the onset of ovulation could not be correlated with a specific day of proestrus or estrus. However, 22/25 LH peaks were detected within ±3 days of the first day of estrus. These results, employing direct ovarian examination and frequent blood sampling, suggest that: 1) the duration of the LH surge in the bitch is prolonged in comparison to most common domestic animals; 2) most ovulations in the bitch occur 24–72 h following peak serum LH concentrations; 3) a specific day of standing estrus is not precisely related to the onset of the LH surge in the bitch and therefore cannot be used as an accurate estimate of time of ovulation in this species.