Interval from hCG, deslorelin, or histrelin administration. The duration from administration of hCG, deslorelin acetate, or histrelin to subsequent ovulation is reasonably consistent, provided that the guidelines for administration are followed. Administration of hCG will typically result in ovulation in 24–48 hours, with an average of 36 hours. Administration of deslorelin or histrelin will usually result in ovulation in 36–42 hours, with an average of 40 hours. Administration of an ovulation induction agent at an appropriate time during estrus will typically advance the ovulation by 1–2 days prior to the day of the expected spontaneous ovulation.
Uterine edema pattern during ultrasound examination. Endometrial edema develops in response to the presence of estradiol and the absence of progesterone. In most mares, a predictable pattern of edema development and regression occurs during each heat period (Figure 9.1, see Chapter 8). Estradiol‐17β concentrations and the amount of edema both peak 1–2 days prior to ovulation. Ovulation typically occurs when edema is in a stage of decline or is absent.
Thickness of the follicular wall. Ultrasound examination of the developing dominant follicle will reveal a relatively thin follicular wall during early to mid‐estrus. Final maturation of the follicle is associated with an increased thickness of the follicular wall due to an increase in vascularity around the follicle and pre‐ovulatory luteinization of granulosa cells. In many cases a hypoechoic ring surrounds a more hyperechoic follicular wall. In contrast, the wall of a diestrus or early estrus follicle is not distinguishable from the surrounding ovarian tissue.
Shape of the follicle. The pre‐ovulatory follicle is typically round or slightly oval as viewed during a two‐dimensional ultrasound evaluation. A “cone” or “point” may develop as the follicle tunnels toward the ovulation fossa in the hours preceding ovulation.
Vascularity with Doppler ultrasound. Examination of the dominant follicle by Doppler ultrasound will reveal an increase in vascularity surrounding the follicle between 36 and 12 hours prior to ovulation followed by a decrease in color Doppler signals during the last 4 hours prior to ovulation (see Chapter 76).
Degree of cervical relaxation. The physical characteristics of the cervix change throughout the estrous cycle due to the varied influence of estrogen and progesterone. These characteristics can be visualized on speculum examination and tone can be detected by manual palpation per rectum (see Chapter 10). A mare in heat, in the presence of estradiol 17β and an absence of progesterone will have a cervix that is relaxed and draped onto the floor of the vagina, that is pink in color and moist. In contrast, a mare in diestrus will have a cervix that is high on the cranial vaginal wall and is closed tight, dry, and pale in color.Figure 9.1 Pattern of endometrial edema relative to ovulation.
Peri‐ovulatory ovarian pain on palpation. Many mares will exhibit discomfort when the site of a fresh ovulation is palpated per rectum. Some mares will also be sensitive to palpation of the ovary as the time of ovulation approaches.
Further Reading
1 Ginther OJ. 1979. Reproductive Biology of the Mare: Basic and Applied Aspects. Cross Plains, WI: Equiservices.
2 McCue PM, Scoggin CF, Lindholm ARG. 2011. Estrus. In: McKinnon AO, Squires EL, Vaala WE, Varner DD (eds). Equine Reproduction, 2nd edn. Ames, IA: Wiley Blackwell, pp. 1716–27.
10 Speculum Examination of the Vagina
John J. Dascanio
School of Veterinary Medicine, Texas Tech University, USA
Introduction
A visual vaginal examination should be performed as part of a complete mare breeding soundness examination. A speculum examination may also be used to confirm the stage of the mare’s estrous cycle and to observe the vagina for pathology such as urine pooling, varicosities, adhesions and cervical inflammation, or discharge. A disposable aluminum foil‐covered tube speculum, a glass tube speculum (Figure 10.1), or a tri‐valve Polansky (Caslick) speculum (Figure 10.2) may be used for the examination. The glass tube speculum tends to transmit more light into the vagina than the disposable aluminum tube speculum. The tri‐valve Polansky (Caslick) speculum will provide a wider view of the cranial vagina and cervix, but may obscure the vagina in areas corresponding to the speculum arms.
The mare should have a relaxed external cervical os lying on the floor of the cranial vaginal vault and a pink, glistening vaginal mucosa during estrus. During diestrus, the external cervical os will be toned or closed and located high on the cranial wall of the vaginal vault, with a pale pink, dull, or dry vaginal mucosa. In anestrus, the cervix may be relaxed with a pale, dry mucous membrane. There should not be any discharge from the external cervical os and there should be no fluid accumulation on the floor of the vagina (e.g., urine pooling). The longer the speculum is in the vagina, the more air will irritate the mucosa, causing the mucous membranes to become redder and more congested. Infection may cause an increase in vascularity and redness to the vagina and yellow to white discharge may also be present from the cervical os. During pregnancy, the vagina will often have thick mucus present causing the vaginal walls to stick together. In addition, the cervix during pregnancy may have an accumulation of thick mucus visible (mucus plug).
Equipment and Supplies
Tail wrap, tail rope, non‐irritant soap, roll cotton, stainless steel bucket, disposable liner bag for bucket, paper towels, exam gloves, sterilized glass speculum or disposable aluminum foil speculum, sterilized tri‐valve Polansky (Caslick) speculum, sterile lubricant, light source, uterine culture swab, bacterial/fungal transport media.
Technique
Remove feces from the rectum.
Place a tail wrap and tie the tail out of the way (see Chapter 4).
Clean and dry the perineum of the mare (see Chapter 3).
Lubricate the end of the speculum with sterile lubricant. With the tube speculums, lubricant should not get into the lumen of the speculum so as to avoid obscuring visualization of the reproductive tract.Figure 10.1 Use of a glass vaginal speculum.Figure 10.2 Inserting a tri‐valve Polansky (Caslick) speculum.Figure 10.3 Turning the wing nut to open the tri‐valve Polansky (Caslick) speculum.
Wearing exam gloves, separate the lips of the vulva and insert the speculum in an upward manner to pass over the ventral pelvic brim.
Once over the brim, bring the speculum to a horizontal orientation. Caution is advised when elevating the speculum to a horizontal plane as some mares will react when pressure is placed onto the perineal body.
The tri‐valve Polansky (Caslick) speculum is initially turned sideways to allow entry into the vulva (Figure