1. Introduction

The most common cause of failure to conceive in the bitch is poor breeding management (lack of viable semen in the bitch's reproductive tract at a time that will support conception). Thus, identification of the fertile period will ensure that breedings occur at the proper time.¹

1.1. The Estrous Cycle

The bitch estrous cycle is divided into four phases: the first, called proestrus, is the part where the vulva swells and a bloody vaginal discharge occurs. It lasts approximately 7 to 12 days and the bitch is neither fertile nor will she accept the male during this time.

However, males, especially those without experience, are frequently attracted to the bitch at this time. The second part, called estrus, lasts 5 to 7 days. During this stage, there is usually a straw-colored discharge (sometimes with blood). Ovulation occurs at this time, the bitch is fertile and will usually accept the male for breeding. The third and fourth parts are called diestrus and anestrus respectively. During this time, the bitch is not fertile and is not interested in the male.²

1.2. Monitoring of the Estrous Cycle

The estrous cycle of a bitch should be monitored on the physical, clinical and behavioral.

1.2.1. Physical Examination

Physical examination is to assess the vulva and vagina bitch set and things like swelling and secretion (color, thickness, smell) should be considered. Regarding the vulva in proestrus and estrus phase and this is swollen, and the stage of diestrus and anestrus swelling subsides.

The vagina examination may be performed by vaginoscopy where staining is observed and swelling of the wall. The vaginal mucosa, as a target organ for reproductive hormones, reflects changes in their levels as the estrous cycle progresses. The observation of these changes via vaginoscopy can be a quick, useful tool to use in ovulation timing³ but requires practice by the operator for correct interpretation of findings. As with vaginal cytology, the anterior vagina should be examined to provide reliable information. In proestrus, the vaginal mucosa becomes markedly edematous as estrogen levels increase. As estrus approaches, declining estrogen and rising progesterone levels cause the edema to subside. The vaginal tissue, however, is stretched and cannot rebound quickly enough to accommodate the loss of fluid. As a result, vaginal folds collapse, and subtle surface wrinkling/crenulation becomes apparent on the vaginal mucosa at the time of the LH surge. By diestrus, the mucosa is flat and variegated. Since the protective layers of epithelium have diminished, the mucosa is friable, and so patches of superficial hemorrhages are often seen.¹

1.2.2. Clinical Examination

Clinical tests to monitor the estrous cycle of the bitch are based on vaginal cytology and hormonal dosages.

1.2.2.1. Vaginal cytology³

In proestrus the vaginal epithelium proliferates which leads to a change of epithelial cells from round faintly staining epithelial cells to intermediate and parabasal cells which stain more intensely and are more angular on the edges. Typically, red blood cells are present in large numbers and few neutrophils should be seen. Large numbers of extracellular bacteria are also often present.

In the estrous the vaginal cytology is predominated by cornified epithelial cells, large darkly staining angular epithelial cells without an identifiable nucleus. Some bitches will undergo full cornification, which is 100% of the cells present are of this type. However, some bitches will not exceed 70% and some will continue to show red blood cells on the cytology throughout estrus. This is one reason vaginal cytology is not specific enough to be used exclusively for challenging cases. The other reason vaginal cytology alone is insufficient for timing breedings is that the cytology will remain cornified for up to 7 days, but the bitch's peak fertility lasts only 2 to 3 days, and fragile semen is viable for 12 to 24 hours.

The onset of diestrus is marked by a rapid decline in the number of superficial angular cells and reappearance of rounder nucleated intermediate and parabasal cells. White blood cells may appear in large numbers but do not look active. There are usually no red blood cells present. Most commonly, the cellular profile changes within a single day from essentially 100% superficial cells to less than 20% superficial cells. Anestrus non-cornified cells are the predominant cell type present.

1.2.2.2. Hormonal dosages⁴

Progesterone is the hormone assay most commonly used for assessment of ovulation date in bitches. Because bitches undergo preovulatory luteinization, rise in serum progesterone concentrations can be used to infer date of the LH peak and prospectively predict ovulation day. In general, progesterone concentration on the day of the LH peak will be about 2.0 ng/ml and on ovulation day from 4 to 10 ng/ml. Progesterone can be measured using in-house assays or commercial assays. Commercial laboratories usually use either radioimmunoassay (RIA) or chemiluminescence assay (CA). These assays are quantitative. One study comparing RIA to CA demonstrated good correlation between the two when used to assay aliquots from the same sample. In-house assays are enzyme-linked immunosorbent assays (ELISAs); those available in the United States are semiquantitative, with various shades of color corresponding to ranges of serum progesterone concentration. Semiquantitative ELISA is less accurate than either RIA or CA. The primary advantage of ELISA assay is quick turn-around time as it can be run in-house.

Direct measurement of LH is the most definitive diagnostic test available. Unfortunately, commercial LH assays are not readily available for the bitch and turn- around time makes their use impractical for clinical cases.

1.2.3. Behavioral Change⁵

The frequency of urination of the bitch increases as she progresses through proestrus and at this stage even promoting attraction of males by releasing the Pheromones, the female does not accept mating.

The period of behavioral estrus is variable. Female dogs may passively accept the attentions of the male and she will probably flag (hold her tail to one side, if she has one) and stand solidly when pressure is applied over her rump.

2. Conclusions

The importance of methods in association bitches heat monitoring is based on the improvement of fertility of animals with high genetic and financial value. So it is important to remember the associations that may be used and especially when requesting each evaluation

References

1.  Goodman M. Ovulation timing concepts and controversies. Vet Clin Small Anim. 2001;31(2):219–235.

2.  Greer ML. Preparing to breed. In: Canine Reproduction and Neonatology: a practical guide for veterinarians, veterinary staff, and breeders.Teton NewMedia; 2014:38–51.

3.  Jeffcoate LA, Lindsay FEF. Ovulation detection and timing of insemination based on hormone concentrations, vaginal cytology and the endoscopic appearance of the vagina in domestic bitches. J Reprod Fertil. 1989;39(suppl):277–287.

4.  Kustritz MVR. Managing the reproductive cycle in the bitch. Vet Clin Small Anim. 2012;42:423–437.

5.  Kustritz MVR. Reproductive behavior of small animals. Theriogenology. 2005;64(3):734–746.