Physical characteristics of the uterus during the bovine estrous cycle and early pregnancy

Uterine tone, uterine contractility and endometrial echotexture were monitored daily in heifers during the estrous cycle (n = 6; Days 0 to 21; ovulation = Day 0) and during early pregnancy (n = 7; Days 0 to 26). Uterine tone was assessed by transrectal palpation and scored from 1 (flaccid) to 5 (turgid) by an operator who had no knowledge of reproductive status, day, or group. The main effect of day was significant, but the group effect and the group-by-day interaction were not. Uterine tone scores were high during the periovulatory period (Days--1, 0, 1), decreased (P < 0.05) to low levels on Days 3 and 4, and then increased (P < 0.05) from Days 4 to 10. The increase in tone during early diestrus was confirmed (P < 0.05) in a second experiment. Uterine contractility was assessed by transrectal ultrasonography during a five-minute scan of the caudal portions of the uterine horns and scored from 1 (minimal contractility) to 4 (maximal contractility). The main effects of day and the group-by-day interaction were significant. Contractility scores in both groups were highest just before or on the day of ovulation (Days--1,0) and then decreased (P < 0.05) until Day 11. After Day 16, the scores increased (P < 0.05) in the nonbred heifers and remained low in the pregnant heifers. Endometrial echotexture scores were different among days (P < 0.0001), between the 2 groups (P < 0.02), and for the group-by-day interaction (P < 0.0001). Echotexture scores in both groups peaked just before ovulation (Day--1) and then decreased (P < 0.05) until Day 4. After Day 16, the scores increased in the nonbred group but remained low in pregnant heifers. In summary, uterine contractility and endometrial scores had similar profiles, being high during the periovulatory period and low thereafter; the levels rose in association with the end of the interovulatory interval in nonbred heifers, but remained at low levels in pregnant heifers. Uterine tone scores were also high during the periovulatory period and decreased to low levels several days postovulation, but then, in contrast with the other end points, began to increase in both the nonbred and pregnant heifers.

Associations between emergence of follicular waves and fluctuations in FSH concentrations during the estrous cycle in ewes

Folliculogenesis was studied daily in 16 interovulatory intervals in 5 Polypay ewes from mid February through April using transrectal ultrasonic imaging. The 3-mm follicles attaining > or = 5 mm on Days--1 (ovulation=Day 0) to 11 showed significant peak numbers on Days 0, 5 and 10. The number of 3- and 4-mm follicles that did not reach > 4 mm was not significant, indicating that these follicles did not manifest a wave pattern. A follicular wave was defined as one or more follicles growing to > or = 5 mm; the day the follicles were 3 mm was the day of wave emergence, and the first wave after ovulation was Wave 1. Waves 1, 2 and 3 emerged on Days -1 to 2,4 to 7 and 8 to 10, respectively. Four interovulatory intervals in April were short (9 to 14 d), indicating the end of the ovulatory season. In the remaining 12 intervals, the ovulatory wave was Wave 3 in one interval, Wave 4 in 8 intervals, and Wave 5 or 6 in 3 intervals. The ovulatory wave followed the rhythmic pattern of Waves 1 to 3 by emerging on Days 11 to 14 in 50% of the intervals. In the remaining intervals, either the ovulatory wave was Wave 4 but did not emerge until Day 16 or other waves intervened between Wave 3 and the ovulatory wave. The longest intervals (22, 24 and 24 d) had >4 waves. Based on a cycle-detection program, peak values of FSH fluctuations were temporally associated with the emergence of waves as indicated by the following: 1) tendency (P < 0.08) for an increase in FSH concentrations between 3 and 2 days before emergence of a wave; 2) close agreement between mean number of waves per interval (mean +/- SEM, 4.1 +/- 0.3) and mean number of identified FSH fluctuations (4.5 +/- 0.3); 3) close agreement in length of interwave intervals (4.0 +/- 0.3) and interpeak (FSH) intervals (3.6 +/- 0.2); 4) positive correlation (r(2)=0.8) for number of the 2 events (follicular waves and FSH fluctuations) within intervals; and 5) a closer (P < 0.01) temporal relationship between the 2 events than would have been expected if the events were independent. The results support a relationship between transient increases in FSH concentrations and emergence of follicular waves throughout the interovulatory interval in Polypay ewes, with the 2 events occurring approximately every 4 d.

Follicular dynamics during the ovulatory season in goats

Growth and regression of ovarian follicles>or=3 mm were studied by transrectal ultrasonography for 4 interovulatory intervals in each of 5 Saanen goats. The observed number of growing identified 4-mm follicles per day differed (P<0.05) from randomness, indicating that follicles, on the average, emerged in groups (waves). Averaged over all interovulatory intervals, the number of 3-mm follicles on each day that later reached >or=6 mm followed a pattern of significant peaks on Days 0 (ovulation), 4,8 and 14. A follicular wave was defined by consecutive days of entry of follicles>or=6 mm into the wave, and the day of emergence was defined as the first day that the >or=6 mm follicles were 3 mm. In 15 of 20 (75%) interovulatory intervals, 1 wave emerged during each of Day -2 to Day 1 (Wave 1); Days 2 to 5 (Wave 2); Days 6 to 9 (Wave 3); and Days 10 to 15 (Wave 4). Ovulation occurred during Wave 4. The mean days of emergence of Waves 1 to 4 were Days -1, 4, 8 and 13, respectively. However, in 5 of these 15 interovulatory intervals, 50% of the apparent waves merged or were continuous so that a distinction could not be made between 2 waves. The largest follicle grew to a larger (P<0.05) maximum diameter for Waves 1 (8.7+/-0.3 mm) and 4 (9.7+/-0.3 mm) than for Waves 2 (7.2+/-0.2 mm) and 3 (7.3+/-0.2 mm). The following observations suggested that the phenomenon of follicular dominance was more common during Waves 1 and 4 than during Waves 2 and 3: 1) the interwave intervals (days) were longer (P<0.05) for Waves 1 (3.4+/-0.2) and 4 (4.3+/-0.6) than for Waves 2 and 3 (2.5+/-0.2 for each wave) and 2) the correlation between maximum diameter of largest follicle and the subsequent interwave interval was significant for Waves 1 and 4 but not for Waves 2 and 3. The 5 remaining interovulatory intervals were irregular and involved more than 4 waves, including 2 interovulatory intervals with prolonged follicular phases (14 and 21) and failures of ovulation. In conclusion, the predominant follicular-wave pattern was 4 waves with ovulation from Wave 4, and apparent follicular dominance was expressed during some follicular waves, especially during Waves 1 and 4.

Effect of the dominant follicle on regression of its subordinates in heifers

The relationship between a dominant follicle of a follicular wave and the suppression of subordinate follicles was studied during the first postovulatory wave (Wave 1) in Holstein heifers. The dominant follicle (largest follicle) was cauterized or a sham-operation was done on day 3 (day 0 = ovulation) using seven heifers per group. In the cautery group, compared to the controls, the largest subordinate follicle attained a larger diameter (11 7 vs 8 0 mm; P < 0.01), reached maximum diameter at a later day (day 9.2 vs. day 3.1; P < 0 01) and began to regress at a later day (day 14.3 vs. day 5.7; P < 0.01). In addition, the emergence of Wave 2 was hastened (day 6.4 vs. day 9.3; P < 0.05) and more heifers had more than two waves per interovulatory interval (5 of 6 vs. 2 of 7; P < 0.05). In heifers with the dominant follicle eliminated, the largest subordinate grew to the diameter of a dominant follicle during Wave 1 (n = 3) or became the dominant follicle of a newly emerged wave (n = 2). A subordinate sometimes persisted as a small follicle (e.g., 5 mm) for several days before resurging. However, it was not convincingly demonstrated that a subordinate follicle could resurge after it had begun to regress (decrease in diameter). Results supported the hypothesis that suppression of subordinate follicles is a prolonged process, so that resurgence of a subordinate can occur if the dominant follicle is removed. Key words: Ovaries, follicular waves, selection, cattle, cauterization

Embryo recovery from mares exposed to a year-to-year artificially prolonged daylength

The aim of the experiment was to determine the effect of a year-to-year prolonged daylength on the patterns of equine reproductive activity and results of embryo recovery. Experiments using Konik Polski mares were conducted over four reproduction seasons. Five mares were exposed to a regimen of artificially prolonged daylength (APD) and another five mares in a control group were kept under conditions of natural daylight. Both the control and experimental groups were examined for appearance of estrus, ovulation and also for the state of their coats. A single stallion was used for breeding all of the mares. The embryos were recovered nonsurgically 6 to 9 days after ovulation. All of the mares exposed to APD showed increased ovarian activity, which commenced earlier than in the control group. About 19% more ovulations were detected in the experimental group. The average number of ovulations per lighted mare per year was 15.3, while in the control group it was 12.4 ovulations (P<0.05). However, the embryo recovery rate and total number of embryos obtained from the mares exposed to APD did not exceed the number of embryos collected from the control mares (P<0.05). Modification of daylength had a visible effect on the mares by producing a change in their coats.