Fig 1.
Representative images of the transrectal ultrasonography procedure in plains zebra (Equus quagga) mares.
After 16 months of intensive training, the zebra mares (pictured: “Pepita”) were able to be loaded into the palpation stock, haltered, tied, palpated, and scanned ultrasonographically. For each scanning procedure, a handler stayed by the zebra’s head, while the ultrasound operator would transrectally palpate and then scan the animal. Images of the transrectal ultrasonography scanning are shown, with a preovulatory follicle seen on the left of the ultrasound monitor and a cross-section of the uterus shown on the right. Ultrasonography procedures of all zebra mares occurred daily without sedation and lasted approximately 5–10 min per zebra. The ultrasonographer pictured in this figure has given written informed consent (as outlined in PLOS ONE’s consent form) to publish their likeness in this manuscript. Pictures printed with permission from Lawrence O. Barros, original copyright 2011.
Fig 2.
Representative images of ultrasonographic structures in the plains zebra (Equus quagga) mare reproductive tract.
Antral follicles at different stages can be seen, including (A) early growing follicles, (B) a future dominant follicle next to a small follicle, and (C) a preovulatory follicle. (D) A large, early corpus luteum (CL; arrow) can be seen next to a small follicle. (E) A regressing CL (arrow) is pictured. The uterus is shown in different stages of the zebra estrous cycle with the (F) bifurcation of the uterine horns during diestrus, (G) uterine body during diestrus, and (H) a cross-section of the uterine horn during estrus.
Table 1.
Mean (± SEM) length of intervals, diameters, and growth rates of the future ovulatory follicle, diameters of the three largest follicles, daily follicle count for each class, and number of follicular waves during the interovulatory interval (IOI) in plains zebra (Equus quagga) mares.
Fig 3.
Diameter of the three largest follicles and numbers of total follicles and follicles of different diameter classes during the interovulatory interval of plains zebra mares (Equus quagga).
Mean (± SEM) (A) diameters of the three largest follicles and (B, C) numbers of (B) total follicles and (C) follicles of different diameter classes observed during spontaneous estrous cycles in plains zebra mares (n = 9 cycles in 4 zebras) are shown. (A) Follicles were ranked by size without day-to-day identity. (A, C) Different colors indicate different-sized follicles. The length of the interovulatory interval for all cycles was truncated at Day 32 for statistical comparison. F1, first largest follicle; F2, second largest follicle; F3, third largest follicle.
Fig 4.
Diameters of ovulatory follicles and endometrial echotexture scores in plains zebra (Equus quagga) mares.
Mean (± SEM) diameters of ovulatory follicles from (A, B) single vs. double ovulations and from (C, D) each animal (A, C) during the interovulatory interval (IOI) and (B, D) during the preovulatory period of spontaneous estrous cycles in plains zebra mares (n = 9 cycles in 4 zebras) are shown. Different colors indicate different (A, B) types of ovulations (single vs. double) and (C, D) zebra mares. (B) Mean (± SEM) endometrial echotexture scores for all spontaneous estrous cycles combined are also shown. The length of each IOI (indicated by the day of ovulation) varied between 33 and 41 days; therefore, the IOI for all cycles was truncated at Day 32 for statistical comparison. * Indicates the first significant increase and decrease (P < 0.05) when compared to the peak endometrial score. All data were transformed using rank or log10, then analyzed using one-way ANOVA followed by post hoc Tukey’s tests when applicable. F, follicle; D, day; FD, follicle by day interaction; NS, non-significant; Z, zebra; ZD, zebra by day interaction.
Fig 5.
Diameters of all antral follicles during two spontaneous estrous cycles in four plains zebra (Equus quagga) mares.
All follicles were tracked from the start of ultrasonographic scanning until ovulation of the preovulatory follicle(s). Different colors indicate different individual follicles. Arrow indicates day of ovulation, with synchronous double ovulations superimposed (i.e., Devassa, Cycle 2). OV, ovulation day.
Table 2.
Mean (± SEM) length of intervals, diameters, and growth rates of the future ovulatory follicle, diameters of the three largest follicles, and daily follicle count for each class from prostaglandin administration to Day –1 in plains zebra (Equus quagga) mares.
Fig 6.
Diameters of all antral follicles during five induced ovulatory cycles in two plains zebra (Equus quagga) mares (n = 10 cycles total).
All follicles were tracked from the start of ultrasonographic scanning until ovulation of the preovulatory follicle. Different colors indicate different individual follicles. Arrows indicate days of exogenous drug administration or ovulation. PG, prostaglandin analogue (dinoprost tromethamine; Lutalyse) administration; hCG, human chorionic gonadotropin (Vetecor) administration; OV, ovulation day.
Fig 7.
Diameters of preovulatory follicles and endometrial echotexture scores during spontaneous estrous and induced ovulatory cycles in single-ovulating plains zebra (Equus quagga) mares.
Mean (± SEM) (A) preovulatory follicle diameter and (B) endometrial echotexture score for spontaneous estrous and induced ovulatory cycles in single-ovulating plains zebra mares (n = 5 spontaneous cycles in 4 zebras and n = 10 induced cycles in 2 zebras) are shown. Different colors indicate different types of cycle (spontaneous vs. induced). * Indicates significant differences (P < 0.05) in (A) follicular diameter between type of cycle within the same day, and (B) the first significant increase and decrease when compared to the peak endometrial echotexture score within the same type of cycle. # Indicates a tendency (P < 0.1) for a difference in follicular diameter. All data were transformed using rank or log10, then analyzed using one-way ANOVA followed by post hoc Tukey’s tests when applicable. OV, day of ovulation; F, follicle; D, day; FD, follicle by day interaction; E, endometrial score; ED, endometrial score by day interaction; NS, non-significant.