Diagnosis of the estrous cycle in female dogs is important in veterinary medicine. The estrous cycle is divided into the following stages: proestrus, estrus, diestrus, metestrus, and anestrus, which due to the action of hormones, replace one after another. This feature of the estrous cycle leads to some difficulties with reproduction. It is hard to obtain newborns because of prolonged anestrus. Vaginal cytology is a simple and available diagnostic method of the estrous cycle. It is based on the analysis of vaginal mucosa epithelial cells changes. This method is used to determine the time of mating and diagnose pathological conditions in the reproductive system of female dogs. There are various drugs in veterinary medicine for the correction of the estrous cycle in female dogs. We used implant Suprelorin® to estrus induction. There were described methods of estrus stimulation using a subcutaneous implant Suprelorin (4.7 mg, deslorelin) and changes in vaginal epithelial cells using the vaginal cytology method. The study was performed on twelve (n = 12) adult female dogs in the anestrus stage. Implants were injected subcutaneously in the groin area and removed at the beginning of the estrus.

The sexual cycle and ovulation in bitches occur much less often than in other domestic animals, as they are monoestrous. In addition, dogs have spontaneous ovulation and, consequently, a spontaneous luteal phase. This physiology of the sexual cycle in bitches leads to specific difficulties with reproduction. Owners often cannot connect a bitch with a dog in time and, accordingly, get offspring due to the absence of heat or prolonged anestrus. Therefore, the stimulation of the sexual cycle in bitches is gaining more and more interest among animal owners. Understanding the physiology of the sexual cycle and its stages makes it possible to manipulate it safely and without negative consequences for the bitch's body. We recommend using the Suprelorin implant in late anestrus to induce estrus and obtain ovulation in bitches. Implant Suprelorin®, primarily registered for the pharmacological sterilization of dogs and cats, causes estrus at the beginning of its action. This mechanism of action of Deslorelin implants is known as the flare effect due to its stimulating effect on the secretion of gonadotropin (GnRH), which triggers the synthesis of follicle-stimulating and luteinizing hormones from the pituitary gland. Our results showed that the use of the Suprelorin® implant (4.7 mg Deslorelin) is safe for the induction of oestrus in bitches and does not cause side effects. The proposed induction scheme makes it possible to achieve the highest level of initiation of the sexual cycle (hypothalamus-pituitary-gonads), which is as close as possible to the natural sexual cycle regarding the mechanism of action and is safe for the bitch's body. Ultrasound diagnostics occupy an essential place in studying animals with gynecological problems. There are not many studies in bitches that would show the dynamics of ovarian follicles after using the Deslorelin implant. In our studies, ultrasonographic examination of ovarian structures revealed a faster appearance of follicles in the group of bitches treated with the Deslorelin implant (4.7 mg) compared to the control group; at the same time, their size was significantly more extensive, and the ovulated faster. The appearance of anechoic structures on the ovaries with a size of more than 3 mm (mean 3.2 ± 0.1) was detected already on the third day after the introduction of the implant in 3/6 bitches in the experimental group, while in the control group, only on the fifth day (4/6) and on the seventh (2/6) day. Follicle sizes differed statistically between groups from the 9th to the 12th day. In the experimental group, the appearance of follicles was noted earlier than in the control group (starting from the third day); they were significantly more extensive and ovulated on the 14th day, while in the control group, only on the 16th day.

Since bitches are monoestrous animals, their sexual cycle occurs much less often than other domestic animals, and their reproductive capacity is potentially less. That is why manipulations with the sexual cycle of bitches and their correction are gaining more and more interest. Estrus induction is essential to commercial breeding owners for several reasons. Understanding the processes that occur during each stage of the sexual cycle, it can be safely manipulated. There are many methods for stimulating estrus, but not all of them have found their practical application. The implant Suprelorin (4.7 mg Deslorelin), which is primarily registered for the pharmacological castration of dogs and cats, has also found its use for the induction of estrus in bitches, since at the beginning of its activities, it stimulates the secretion of gonadotropin (GnRH), which triggers the synthesis of follicle-stimulating and luteinizing pituitary hormones. This initial mechanism of action of Deslorelin implants is known as the flash effect and causes heat in almost 100 % of bitches. Despite numerous publications on the use of the implant, its impact is still being investigated. The article presents changes in progesterone and estradiol after using the Suprelorin implant for estrus induction and compares the course of an induced sexual cycle with a spontaneous one. The study was conducted on 13 sexually mature bitches, 7 of them received the Suprelorin implant no earlier than 150 days after the last estrus, and 6 of them were bitches with spontaneous estrus, which were included in the control group. The implant was removed at the beginning of estrus when the progesterone level increased above 3 ng/ml. In 6/7 females, this day fell on the 10th day after the implant was inserted, and in 1/7 – on the 9th. Ovulation occurred two days after the LH peak in all bitches from the experimental group, which corresponded to the 12th day in 6/7 bitches and the 11th day in 1/7 bitches from the introduction of the implant. The estradiol peak in the control group was observed faster than in the experimental group. It occurred on average on the 8th day (mediam 8 (7–9)) from the beginning of estrus, in one bitch on the 7th day, in three - on the 8th, and in two – on the 9th day, respectively. In the experimental group, the estradiol peak occurred on the 9th day after the implant (mediam 9 (8–9), in two bitches on the 8th, and five – on the 9th. But the obtained results indicate that in most bitches of the research group, the estradiol peak occurred one day before the LH peak (5/7) and only in 2/7 two days before the LH peak, which is typical for spontaneous estrus, so despite, that,, the peak of estradiol in the experimental group was observed later than in the control group, and ovulation itself occurred faster. Quantitatively, the level of sex hormones was higher in the experimental group, and the sexual cycle was more predictable.