Evaluation of the clinical efficacy of Gonazon implants in the treatment of reproductive pathologies, behavioral problems, and suppression of reproductive function in the male dog

INSL3 Variation in Dogs Following Suppression and Recovery of the HPG Axis

Insulin-like peptide 3 (INSL3) is a constitutive product of mature, adult-type Leydig cells of the testes and consequently in most mammals is an ideal biomarker with which to monitor pubertal development. A new heterologous time-resolved fluorescence immunoassay was developed and validated to measure circulating INSL3 in the blood of adult male dogs. Compared to other species, INSL3 concentration is low with marked variation between individuals, which appears to be independent of breed, age, or weight. A model system was then used in which a cohort of beagle dogs was subject to a GnRH-agonist implant to suppress the HPG axis and spermatogenesis, followed by implant removal and recovery. Unlike testosterone, INSL3 levels were not fully suppressed in all animals by the GnRH agonist, nor was the recovery of Leydig cell function following implant removal uniform or complete, even after several weeks. In dogs, and dissimilar from other species (including humans), Leydig-cell INSL3 appears to be quite variable between individual dogs and only weakly connected to the physiology of the HPG axis after its suppression by a GnRH-agonist implant and recovery. Consequently, INSL3 may be less useful in this species for the assessment of testis function.

Suppression of hypothalamic-pituitary-gonadal function by linzagolix in benign prostatic hyperplasia and polycystic ovary syndrome animal models

The hypothalamic-pituitary-gonadal (HPG) axis is an important regulatory mechanism involved primarily in the development and regulation of the reproductive systems. The suppression of the HPG axis by gonadotropin-releasing hormone (GnRH) analogues is expected to be effective for the treatment of sex hormone-dependent diseases, such as endometriosis, uterine fibroid, prostate cancer, benign prostatic hyperplasia (BPH) and polycystic ovary syndrome (PCOS). Despite the established involvement of GnRH signalling in these disorders, the therapeutic efficacy of small molecular GnRH antagonists for BPH and PCOS has not been adequately evaluated in non-clinical studies. Therefore, the purpose of the present study was to evaluate the potential of linzagolix, a small molecular GnRH antagonist, as a potential new treatment option for BPH and PCOS. Dogs and rats exhibiting normal prostates and dogs diagnosed with prostatic hyperplasia were used to evaluate the effects of linzagolix in BPH. The effects of linzagolix were also examined in a rat model of PCOS induced by repeated administration of letrozole, an aromatase inhibitor. Linzagolix reduced serum luteinizing hormone and testosterone levels in male rats and normal or BPH model dogs and suppressed prostate weight without testosterone depletion, suggesting the existence of an optimal therapeutic testosterone level for BPH treatment. In a PCOS rat model, linzagolix improved both insulin resistance and ovarian dysfunction. Treatment with linzagolix decreased follicle-stimulating hormone levels, but did not alter serum luteinizing hormone and testosterone levels. These results indicate that linzagolix may provide a new treatment option for GnRH-related disorders, such as BPH and PCOS.

The use of a 4.7 mg deslorelin slow release implant in male dogs in the field

OBJECTIVE

Slow-release GnRH agonist implants (SRI) are used for reversible medical downregulation of testicular function in male dogs as an alternative to surgery. The 4.7 mg deslorelin SRI should reduce testosterone after 6-8 weeks and induce castration-like effects for 6 months (mon). However, some individual variation is described in the field in regard to onset and duration of effect. For this reason, we aimed to study the effects of the 4.7 mg deslorelin SRI in a larger cohort.

MATERIAL AND METHODS

In total 50 intact, healthy male dogs (12-48 months, mon; 9-40 kg) were treated with a 4.7 mg deslorelin SRI into the umbilical area (TG, n=45) or served as untreated controls (CG, n=5). CG dogs were surgically castrated after measurement of testicular dimensions and blood sampling for testosterone. In TG, SRIs remained for 5 mon in place and subsequently 3-7 male dogs were surgically castrated at removal (week, W 0) or 1, 2, 3, 4, 5, 6, 7, 8 or 10 weeks later. Examination parameters were testicular dimensions (before treatment, at 4, 8, 12 W, 5 mon, weekly until castration), testosterone (before treatment, at 8 W, 5 mon, castration) and testicular histology (castration).

RESULTS

Whereas examination parameters did not differ between CG and TG before treatment, testicular volume and testosterone was significantly reduced at all time points during treatment. In all but 3 (8 W) and 2 male dogs (5 mon) testosterone was basal during treatment before removal, whereas the parameters were significantly reduced compared to pre-treatment in the respective dogs. After implant removal, testosterone and testicular volumes increased. However, different to earlier studies, the "restart" was more variable with individual basal testosterone until W7, but also physiological testosterone concentrations in W2. Similarly, histological testicular findings at castration were quite variable: besides an arrest on spermatogonia and spermatocytes, elongated spermatids with normal spermatogenesis were found in individual dogs.

CONCLUSION

Our study confirms the efficacy of the deslorelin SRI, but also individual variation especially regarding reversibility of effects on endocrine and germinative testicular function.

CLINICAL RELEVANCE

Deslorelin SRIs offer a suitable alternative to surgical castration with individual variation to be considered when used in clinical practice.

The function of the pituitary-testicular axis in dogs prior to and following surgical or chemical castration with the GnRH-agonist deslorelin

Chemical castration, that is the reduction of circulating testosterone concentrations to castrate levels by administration of a GnRH-agonist implant, is a popular alternative to surgical castration in male dogs. Detailed information concerning the pituitary-testicular axis following administration of a GnRH-agonist implant is still scarce. Therefore, GnRH-stimulation tests were performed in male dogs, prior to and after surgical and chemical castration. This approach also allowed us to determine plasma concentrations of testosterone and oestradiol in intact male dogs for future reference and to directly compare the effects of surgical and chemical castration on the pituitary-testicular axis. In intact male dogs (n = 42) of different breeds GnRH administration induced increased plasma LH, FSH, oestradiol and testosterone concentrations. After surgical castration basal and GnRH-induced plasma FSH and LH concentrations increased pronouncedly. Additionally, basal and GnRH-induced plasma oestradiol and testosterone concentrations decreased after surgical castration. After chemical castration, with a slow-release implant containing the GnRH-agonist deslorelin, plasma LH and FSH concentrations were lower than prior to castration and lower compared with the same interval after surgical castration. Consequently, plasma oestradiol and testosterone concentrations were lowered to values similar to those after surgical castration. GnRH administration to the chemically castrated male dogs induced a significant increase in the plasma concentrations of LH, but not of FSH. In conclusion, after administration of the deslorelin implant, the plasma concentrations of oestradiol and testosterone did not differ significantly from the surgically castrated animals. After GnRH-stimulation, none of the dogs went to pre-treatment testosterone levels. However, at the moment of assessment at 4,4 months (mean 133 days ± SEM 4 days), the pituitary gonadotrophs were responsive to GnRH in implanted dogs. The increase of LH, but not of FSH, following GnRH administration indicates a differential regulation of the release of these gonadotrophins, which needs to be considered when GnRH-stimulation tests are performed in implanted dogs.

What Happens in Male Dogs after Treatment with a 4.7 mg Deslorelin Implant? I. Flare up and Downregulation

Simple Summary

Until now, information about the “flare up” and the time to downregulation in male dogs after treatment with a 4.7 mg deslorelin implant is strongly limited, regarding testosterone concentrations, testicular and prostatic volume and semen quality. The aim of this study was to provide detailed insights into these open questions. GnRH and hCG stimulation tests were performed to gain further insights into testicular endocrine function. Seven male beagle dogs were treated with a 4.7 mg deslorelin implant, and three animals were treated with saline, representing the controls. In deslorelin-treated dogs, first basal testosterone concentrations were observed earliest on D7 and latest on D28 after treatment. Infertility—based on the lack of semen or spermatozoa— was diagnosed earliest on D35 and latest on D77. After five months, the treatment was still effective in six dogs but was reversed in one deslorelin-treated dog.

Abstract

Although registered since 2007, knowledge about changes in testosterone concentrations (T), testicular and prostatic volumes (TV, PV) and semen quality, as well as the time point of infertility following treatment with a 4.7 mg deslorelin (DES) slow-release implant, is limited. Therefore, seven sexually mature male dogs were treated with DES (TG); three male dogs treated with saline served as controls (CG). The study assessed local tolerance, TV, PV, semen parameters and T subsequent to GnRH/hCG stimulation in regular intervals. Local tolerance was good. In TG, T was increased right after treatment, but decreased four hours afterwards. Subsequently, TV, PV, semen quality and T decreased over time in TG, but not CG. T was basal (≤0.1 ng/mL) from D28 onwards. Response to GnRH/hCG stimulation was variable, with two TG dogs having increased T post-stimulation on all study days independent of pre-treatment concentrations. A(zoo)spermia in TG was observed from D35–D77 in all seven dogs. Whereas treatment was still effective in six TG dogs five months after implant insertion, it was fully reversed in one dog in terms of T and spermatozoa on the last examination. These results indicate high variation in individual dogs, necessary to consider when advising dog owners.

Prepubertal Use of Long-Term GnRH Agonists in Dogs: Current Knowledge and Recommendations

The search for an alternative approach of estrus control (induction or suppression) in dogs is an important issue and the use of slow GnRH agonist-releasing implants has been the subject of frequent research in recent years. Studies to date demonstrate that the short- and long-term effects of deslorelin implants applicated at different time points of the prepubertal period are similar to those of adult dogs; however, there are important differences. The age of the prepubertal bitch and the dosage appear to be the main determinants of the response to deslorelin, as well as the individual metabolism of the bitch. Recent studies reported that the deslorelin-mediated long-term delay of puberty does not have negative carry-over effects on subsequent ovarian functionality, serum steroid hormone concentrations, uterine health, and fertility; however, more molecular studies are needed to determine the effects of application time of GnRH agonists on hormone concentrations and peripheral receptor expression. Furthermore, the long-term effects of delay of puberty with deslorelin on joint health, tumor development, the immune system, and social behavior deserve further investigations.

A Comparative Study of the Effects of Osaterone Acetate and Deslorelin Acetate on Sperm Kinematics and Morpho-Functional Parameters in Dogs

Simple Summary

Benign prostatic hyperplasia affects over 80% of old, non-castrated male dogs. In many cases, the severity of the symptoms means that treatment is required. The treatment of choice is surgical castration, which is unacceptable for the owners of stud dogs who are interested in therapy that does not exclude their animals from breeding. In those cases, treatment with deslorelin acetate or osaterone acetate offers an alternative to surgery. The aim of our study was to compare the changes in semen parameters over time. The deslorelin acetate implant gradually, during the course of its action, led to a full prevention the stud dogs from mating. However, in the first week following implant placement, in some individuals we observed an increase in sperm concentration (flare up effect), offering the possibility to obtain sperm in valuable dogs before the action of deslorelin acetate is completely established, precluding semen collection. On the other hand, osaterone acetate allowed for the continuous reproductive use of a stud dog, as it only affected some semen parameters, and mainly caused a temporary reduction in semen volume with the subsequent increase in semen concentration without altering the libido.

Abstract

Benign prostatic hyperplasia (BPH) is one of the most common problems in older male dogs that often has a huge impact on their health and welfare. This article presents a comparison between osaterone acetate (Ypozane^®; Virbac^®)(OA) and deslorelin acetate (Suprelorin^®; Virbac^®)(DA), medications that are the main therapeutic alternative to castration in dogs with BPH. Forty dogs were divided into four groups: I—negative control (five dogs without BPH); II—positive control (10 individuals diagnosed with BPH); III—15 dogs treated with DA, and IV—10 individuals treated with OA. Semen fractions were collected on days 0 (day of treatment), 7, 14, and 21, and weeks 8, 12, 16, and 20. Macroscopic, microscopic and CASA analyses were performed. Both DA and OA significantly affected the properties of the canine ejaculate. The DA lead to the lack of libido and had lesser effects to the sperm function before it caused azoospermia, whereas OA had no effect on libido and only temporary reduction in seminal plasma volume was observed, which resulted in temporary deterioration in the percentage of motile and progressive spermatozoa.

Effect of drugs on fertility in male dogs: A review

The aim of this literature review is to present and discuss the available data on the effects of drugs on male dog fertility. Apart from hormones and antihormonal agents, there is still only little information available regarding the effect of other drugs on sexual function and fertility in male dogs. A negative impact on fertility in male dogs has been reported for vincristine, cyclophosphamide, tetracycline and ketoconazole. However, preclinical safety studies of drugs for human use indicated that spermatogenesis in dogs may be sensitive to a wide variety of drugs. Thus, in cases of reduced fertility or infertility in male dogs, medical treatment should always be considered. In most cases, the effects of drugs on sexual function and spermatogenesis are reversible after the discontinuation of the drug. Further studies on the effects of drugs on male dog fertility are needed.

Post-castration prostatic involution: A morphometric and endocrine study of healthy canines and those with benign prostatic hyperplasia

The objective of this study was to evaluate the effect of castration on dimensions of the prostate by B-mode ultrasound for 90 days, as well as to evaluate changes in serum concentrations of testosterone and oestradiol in clinically healthy canines and those with benign prostatic hyperplasia (BPH). Three groups of animals were used: healthy canines castrated on day 0 (HCC, n = 8), canines with a diagnosis of benign prostatic hyperplasia (BPHC, n = 9) castrated on day 0 and healthy uncastrated canines (IHCC, n = 10). Prostate size was obtained by B-mode ultrasound, while blood samples were collected (days 0, 7, 14, 28, 60 and 90 post-castration) to determine the serum testosterone and oestradiol concentration. Castration did not affect serum oestradiol concentrations. Castration led to a decrease in serum testosterone (reaching values <20 ng/dl in the first week, p < .05), causing a gradual decrease in dimensions of prostate parameters relative to body weight (p < .05). Canines with BPHC had similar prostate dimensions as the IHCC group 2 weeks post-castration. In relation to the prostate's relative parameters, the decrease with time was greater in canines with BPHC than those in the HCC group. When evaluating parameters as a percentage of relative change, the decrease with time was similar in both castrated groups, except for relative length percentage, which presented a more pronounced decline in BPHC canines than HCC canines. In conclusion, castration is an effective, fast and long-lasting treatment for canine patients with BPH, as it causes a rapid decrease in blood testosterone concentrations and a decrease in glandular volume, but does not affect serum oestradiol concentrations. This study did not determine the mechanisms of action, but allowed us to observe (based on morphometric variables) that characteristics of prostate involution after castration differed between canines with BPH and healthy canines.

Anti-Müllerian hormone, testosterone, and insulin-like peptide 3 as biomarkers of Sertoli and Leydig cell function during deslorelin-induced testicular downregulation in the dog

The role of anti-Müllerian hormone (AMH) and insulin-like peptide 3 (INSL3) in male infertility is not fully understood. We used the downregulated testis as a model of gonadotropin-dependent infertility. Serum testosterone and AMH concentrations were studied in five adult male Beagles implanted (day 0) with 4.7 mg deslorelin (Suprelorin®, Virbac) (DES group). Testicular expression of LH receptor (LHR) and androgen receptor (AR), AMH, type 2 AMH receptor (AMHR2), INSL3 and its receptor (RXFP2) was evaluated 112 days (16 weeks) after deslorelin treatment by qPCR and immunohistochemistry, and compared to untreated adult (CON, n = 6) and prepubertal (PRE, n = 8) dogs. Serum testosterone concentration decreased significantly by the onset of aspermia on study day 14 (four dogs) or day 21 (one dog), and was baseline on day 105 (week 15). In contrast, serum AMH started to increase only after the onset of aspermia and reached the maximum detectable concentration of the assay by day 49-105 in individual dogs. Testicular LHR gene expression in DES was lower than in CON and PRE (P < 0.0001), while AR gene expression in DES was similar to CON and significantly higher than PRE (P < 0.0001). Testicular AMH expression in DES was intermediate compared to the lowest mRNA levels found in CON and the highest in PRE (P ≤ 0.006). AMHR2 gene expression was similar between groups. AMH protein was detected in Sertoli cells only, while AMHR2 immunoreactivity was principally detected in Leydig cells which appeared to be increased in DES. INSL3 and RXFP2 gene expression was significantly downregulated in the DES testis along with noticeably weak Leydig cell immunosignals compared to CON. In conclusion, deslorelin treatment caused testicular LH insensitivity without affecting androgen sensitivity, and de-differentiation of Sertoli and Leydig cells. In DES, upregulation of the AMH-AMHR2 feed-back loop and downregulation of the INSL3-RXFP2 feed-forward loop are paracrine-autocrine mechanisms that may additionally regulate testosterone production independent of gonadotropins. Our results support AMH and INSL3 as unique biomarkers and paracrine-autocrine regulators of testis function involved in the intimate interplay between Sertoli and Leydig cells.

Short-term effect of ovariohysterectomy on urine serotonin, cortisol, testosterone and progesterone in bitches

Objective

This study aimed to investigate the short-term effect of ovariohysterectomy on urine levels of serotonin and its relation to levels of cortisol, testosterone and progesterone in female dogs. Seven bitches were studied before surgical ovariohysterectomy and then once a week during 4 weeks. Spontaneously voided urine samples were collected and concentration ratios of hormone/creatinine in urine were analysed.

Results

The bitches had significantly lower levels of cortisol, testosterone, and progesterone 1 week after ovariohysterectomy compared with before and the levels stayed low throughout the study (P ≤ 0.05). Interestingly, serotonin levels tended to increase 4 weeks after surgery (P = 0.08). A positive correlation between cortisol and progesterone was found before and after surgery. After surgery, serotonin was positively correlated with cortisol and progesterone (P ≤ 0.05).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05680-y.

B-Mode and Doppler Ultrasonographic Findings of Prostate Gland and Testes in Dogs Receiving Deslorelin Acetate or Osaterone Acetate

Simple Summary

This article presents the use of ultrasonography (basic and advanced techniques) in dogs suffering from benign prostate hyperplasia (BPH) for the assessment of the effects of two different medications: osaterone acetate (Ypozane^TM), a registered drug for BPH in dogs, and deslorelin acetate (Suprelorin^TM), registered for pharmacological castration in dogs. Based on the obtained results it can be stated that both B-mode and color Doppler Ultrasound imaging techniques are suitable for diagnosis and progress assessment of dogs suffering from BPH. Both investigated medications (osaterone acetate and deslorelin acetate) led to a significant sonographic improvement. Deslorelin acetate reduced prostate volume more slowly, but its effect lasted longer than for osaterone acetate.

Abstract

This article presents B-mode and color Doppler imaging of the prostate and testes in dogs suffering from benign prostate hyperplasia (BPH), and receiving deslorelin acetate (Suprelorin^TM) or osaterone acetate (Ypozane^TM). The study was planned as a controlled clinical trial, dogs were divided into negative control (healthy dogs, n = 10), positive control (dogs with BPH, n = 10), and study groups, III (n = 15), receiving deslorelin acetate (DA), and IV (n = 10), receiving osaterone acetate (OA). The B-mode appearance of the prostate parenchyma improved in all investigated dogs from the DA group, and in 60% of OA dogs. Prostate volume was reduced more quickly with OA (from D14), but lasting for a shorter time (on average up to week 20), compared to DA that reduced the prostate volume more slowly (>8 weeks), but the reduction remained longer (>24 weeks). The systolic peak velocity (SPV) and mean velocity (Vmean) were higher in all dogs diagnosed with BPH, compared to Control Group I. The indices did not change in both Control Groups I and II, whereas in study Groups III and IV they decreased throughout the study period compared to day 0 and Control Group II. In Group III the highest reduction was noted from day 21 to week 8, whereas in Group IV the lowest Vmean was recorded before day 21. Testicular parenchyma and volume changed significantly in Group III receiving DA, and the velocity of blood flow in the testicular artery correlated positively with testicular volume only in this group (III). The present study proved the usefulness of B-mode and color Doppler US imaging techniques for diagnosis and progress assessment of dogs suffering from BPH. The blood flow kinetics (mainly SPV) demonstrated a time association between the blood flow changes registered in the prostatic artery, and the subsequent volumetric and sonographic improvement of the prostate parenchyma. The reduction in flow indices was noted prior to the reduction in prostate volume, suggesting that the sonographic recovery of the prostate tissue, occurs secondarily to the regression of the prostate vascular system. Both investigated medications (osaterone acetate and deslorelin acetate) led to a significant sonographic improvement. Deslorelin acetate reduced prostate volume more slowly, but its effect lasted longer than for osaterone acetate.

[GnRH agonist implants in small animal practice - what do we know 13 years following EU registration?]

The availability of GnRH agonist implants offers the possibility of a reversible, temporary downregulation of endocrine and germinative testicular function in male dogs and hobs. This review provides an overview of the registered indication, the induction of temporary infertility in healthy, intact, sexually mature male dogs (4.7 and 9.4 mg deslorelin) and hobs (9.4 mg deslorelin) as well as various off-label indications. Off-label use requires strict indications, informed consent from the owner and a lack of licensed medication (safe and optimum effect). Off-label indications in the male dog include sexual-hormone dependant (disturbing) behavior, benign prostatic hyperplasia, small adenomas of the hepatoid glands and alopecia X. Successful use of deslorelin implants for estrus suppression in jils, but also for the treatment of hyperadrenocorticism in ferrets in general have been described. Similarly, hormonal castration can be induced in tomcats and queens. The variable time to onset of effect and its duration (extremely variable in some animals) represent a challenge for breeders. No (sufficient) contraceptive activity was identified in male rabbits and male guinea pigs; however, treatment did successfully suppress the estrus cycle in female individuals of these species, as well as reproductive activity in male and female rats. Regarding the use in birds and reptiles, significant species-specific differences exist with regard to efficacy, time until onset of effect and duration of downregulation. In birds, the implant is efficient to fully suppress egg laying in chicken, Japanese quail and psittacids. In doves, egg laying is only significantly reduced. Successful treatment of reproduction-associated (unwanted) behaviour patterns (feather picking, aggression) has also been described. In some male birds, namely zebrafinch and Japanese quail, the deslorelin implant is suitable to reduce testosterone levels. Successful treatment of hormone-dependent tumours (Sertoli-cell tumorus) in budgerigars has been described as well as the modulation of specific behavior in turkeys and an efficacy in facilitating their keeping (i. e. reduction of aggression). In reptiles, only the successful use of deslorelin in iguana has been demonstrated to date.

[Development of a large intraprostatic cyst following the use of a GnRH agonist-implant in a male dog with benign prostatic hyperplasia]

A male dog with benign prostatic hyperplasia and several small intraprostatic cysts was treated with a GnRH-agonist implant containing 4,7 mg deslorelin (Suprelorin^®). Within 2 weeks after the implantation, the prior urethral bleeding worsened. A large intraprostatic cyst was detected sonographically. The patient was subsequently treated with osaterone acetate (0.4 mg/kg p. o. once a day for 7 days) and enrofloxacin (5 mg/kg p. o. once a day for 21 days). The clinical symptoms receded within 10 days. Within one month, the cyst regressed completely. The mechanisms of cyst enlargement are discussed.

Comparison of Clinical Effectiveness of Deslorelin Acetate and Osaterone Acetate in Dogs with Benign Prostatic Hyperplasia

Simple Summary

The article compares the treatment efficacy and adverse effects of two drugs used for benign prostate hyperplasia (BPH) therapy in dogs: Ypozane^TM (osaterone acetate) and Suprelorin^TM (deslorelin acetate). Ypozane^TM is a registered medication for this condition in dogs, whereas Suprelorin^TM is registered for pharmacological castration in dogs. The clinical trial proved both drugs to be safe and effective in reducing BPH-related symptoms in dogs, and the noted adverse effects were only mild—mostly weight gain. With osaterone acetate the clinical improvement was noted sooner (from day 7 onwards) than with Suprelorin^TM (from day 21 onwards), but it lasted shorter up to 24 weeks, while in the Suprelorin^TM group, clinical effect remained stable until the end of the study (36 weeks). Both medications can be recommended for treatment of symptoms related to BPH in dogs, as none of the drugs had serious influence on the general health status and both provided substantial clinical improvement.

Abstract

This article presents the results of a randomized clinical trial, designed to compare the efficacy and therapeutic profiles of Ypozane^TM (osaterone acetate—OA) or Suprelorin^TM (deslorelin acetate—DA) in male dogs with clinical signs of benign prostate hyperplasia (BPH). Forty-five intact male dogs were used in the study. The Group I (negative control) included 10 healthy dogs, the Group II (positive control) included 10 dogs with confirmed BPH and no treatment, whereas Group III and IV consisted of dogs with BPH and treated either with DA (15 dogs) or OA (10 dogs). The clinical response, testosterone and estradiol levels, hematology, biochemistry, and adverse effects incidence were evaluated. Both OA and DA proved to be effective for BPH treatment in dogs, as they allowed for the clinical remission in all treated dogs. The complete alleviation of BPH symptoms was noticed sooner with the use of OA (in 80% of dogs from day 7) compared to DA (in 40% of dogs within the first 21 days). The recurrence of clinical signs related to BPH was observed from week 24 in dogs treated with OA, whereas no relapse was noticed in dogs treated with DA at the end of the 36 weeks of the observation period. In 5 dogs (33%) treated with DA, a flare-up effect (increase in the clinical signs associated with BPH) was noticed on day 7. Despite individual differences in the clinical action, both medications were effective and safe options for the treatment of symptoms related to BPH in dogs.

Gonadotropin-Releasing Hormone (GnRH) Agonist Implants for Male Dog Fertility Suppression: A Review of Mode of Action, Efficacy, Safety, and Uses

At present, only surgical sterilization is available for veterinarians and pet owners seeking suppression of fertility in male dogs, in most countries. An alternative contraceptive alternative approach is GnRH releasing implants that desensitize the pituitary to the stimulatory effects of GnRH and thereby block testicular function (testosterone and sperm production). Two GnRH agonists (deslorelin and azagly-nafarelin) have been researched in controlled release formulations for this purpose. A deslorelin-releasing biodegradable implant, marketed under the name Suprelorin®, has been available in Australia and New Zealand since 2007, the European Union (EU) since 2008, and received regulatory approval in China and Mexico in late 2019. Two versions of the implant are available, one labeled for a minimum of 6 months of fertility suppression in male dogs, and the other for a minimum of 12 months in male dogs. Another GnRH agonist (azagly-nafarelin) was also included in a solid implant (Gonazon®). Research results showed it delivered 6-months to 1 year of suppressed fertility; however, it is not commercialized. This review paper summarizes research on the mechanism of action for these technologies and compiles and interprets the research on efficacy and safety. New findings on usage of the deslorelin releasing implant in countries where veterinarians and pet owners have this option is shared. Research on off-label use of the product in male dogs is also reviewed. This review aims to aid in the evaluation of the deslorelin releasing implant as an adjunct or alternative for surgical sterilization of male dogs.

The Effectiveness of Dog Population Management: A Systematic Review

The worldwide population of domestic dogs is estimated at approximately 700 million, with around 75% classified as "free-roaming". Where free-roaming dogs exist in high densities, there are significant implications for public health, animal welfare, and wildlife. Approaches to manage dog populations include culling, fertility control, and sheltering. Understanding the effectiveness of each of these interventions is important in guiding future dog population management. We present the results of a systematic review of published studies investigating dog population management, to assess: (1) where and when studies were carried out; (2) what population management methods were used; and (3) what was the effect of the method. We evaluated the reporting quality of the published studies for strength of evidence assessment. The systematic review resulted in a corpus of 39 papers from 15 countries, reporting a wide disparity of approaches and measures of effect. We synthesised the management methods and reported effects. Fertility control was most investigated and had the greatest reported effect on dog population size. Reporting quality was low for power calculations (11%), sample size calculations (11%), and the use of control populations (17%). We provide recommendations for future studies to use common metrics and improve reporting quality, study design, and modelling approaches in order to allow better assessment of the true impact of dog population management.

Validation of a noninvasive diagnostic tool to verify neuter status in dogs: The urinary FSH to creatinine ratio

Determining the presence of functional gonadal tissue in dogs can be challenging, especially in bitches during anestrus or not known to have been ovariectomized, or in male dogs with nonscrotal testes. Furthermore, in male dogs treated with deslorelin, a slow-release GnRH agonist implant for reversible chemical castration, the verification of complete downregulation of the hypothalamic-pituitary-gonadal (HPG) axis can be difficult, especially if pretreatment parameters such as the size of the testes or prostate gland are not available. The aims of this study were to validate an immunoradiometric assay for measurement of FSH in canine urine, to determine if the urinary FSH to creatinine ratio can be used to verify the neuter status in bitches and male dogs, as an alternative to the plasma FSH concentration, and to determine if downregulation of the HPG axis is achieved in male dogs during deslorelin treatment. Recovery of added canine FSH and serial dilutions of urine reported that the immunoradiometric assay measures urinary FSH concentration accurately and with high precision. Plasma FSH concentrations (the mean of two samples, taken 40 minutes apart) and the urinary FSH to creatinine ratio were determined before gonadectomy and 140 days (median, range 121-225 days) and 206 days (median, range 158-294 days) after gonadectomy of 13 bitches and five male dogs, respectively, and in 13 male dogs before and 132 days (median, range 117-174 days) after administration of a deslorelin implant. In both bitches and male dogs, the plasma FSH concentration and the urinary FSH to creatinine ratio were significantly higher after gonadectomy, with no overlapping of their ranges. Receiver operating characteristic analysis of the urinary FSH to creatinine ratio revealed a cut-off value of 2.9 in bitches and 6.5 in males to verify the presence or absence of functional gonadal tissue. In male dogs treated with deslorelin, the plasma FSH concentrations and urinary FSH to creatinine ratios were significantly lower after administration of the implant, but their ranges overlapped. We conclude that the urinary FSH to creatinine ratio can be used to verify the neuter status of bitches and male dogs. However, it cannot be used for the assessment of complete downregulation of the HPG axis after administration of a deslorelin implant. The urinary FSH to creatinine ratio is preferable over the plasma FSH concentration because it involves only one sample that can be collected relatively easy and noninvasively.

Status of the down-regulated canine testis using two different GNRH agonist implants in comparison with the juvenile testis

Testicular function in the dog was down-regulated using two different GNRH agonist implants, with adult and juvenile testes serving as controls. Treatment resulted in an increased percentage of the interstitial area and decreased area of Leydig cell nuclei. Expression of StAR and the steroidogenic enzymes cytochrome P450 side-chain cleavage enzyme (P450scc, CYP11A1) and cytochrome P450 17α-hydroxylase-17,20-lyase (P450c17, CYP17A1) in Leydig cells was blocked at the mRNA and protein level, showing no differences between the two agonists. Staining for androgen receptor (AR) by immunohistochemistry was positive in Sertoli, Leydig and peritubular cells and some spermatogonia, with in situ hybridization confirming expression in Sertoli cells. At the mRNA level, expression of AR was not affected; however, translation was blocked (reduced percentage of AR-positive Sertoli cells), with the number of nuclei in basal position being decreased. In the juvenile testes, mRNA expression of StAR, CYP11A1 and CYP17A1 was higher compared with the other groups but distinctly lower for the AR. At the protein level, the expression was at the limit of detection for StAR; AR-positive Sertoli cells were not detected. Our observations show that the down-regulated testis is different from the juvenile one rather resembling the testicular status in seasonal breeders out of season.

Nonsurgical fertility control for managing free-roaming dog populations: a review of products and criteria for field applications

About 75% of dogs worldwide are free to roam and reproduce, thus creating locally overabundant populations. Problems caused by roaming dogs include diseases transmitted to livestock and humans, predation on livestock, attacks on humans, road traffic accidents, and nuisance behavior. Nonsurgical fertility control is increasingly advocated as more cost-effective than surgical sterilization to manage dog populations and their impact. The aims of this review were to 1) analyze trends in numbers of scientific publications on nonsurgical fertility control for dogs; 2) illustrate the spectrum of fertility inhibitors available for dogs; 3) examine how differences between confined and free-roaming dogs might affect the choice of fertility inhibitors to be used in dog population management; and 4) provide a framework of criteria to guide decisions regarding the use of nonsurgical fertility control for dog population management. The results showed that the 117 articles published between 1982 and 2011 focussed on long-term hormonal contraceptives, such as gonadotropin-releasing hormone agonists, immunocontraceptives, and male chemical sterilants. The number of articles published biennially increased from one to five papers produced in the early 1980s to 10 to 20 in the past decade. Differences between confined dogs and free-roaming dogs include reproduction and survival as well as social expectations regarding the duration of infertility, the costs of sterilization, and the responsibilities for meeting these costs. These differences are likely to dictate which fertility inhibitors will be used for confined or free-roaming dogs. The criteria regarding the use of fertility control for dog population management, presented as a decision tree, covered social acceptance, animal welfare, effectiveness, legal compliance, feasibility, and sustainability. The review concluded that the main challenges for the future are evaluating the feasibility, effectiveness, sustainability, and effects of mass nonsurgical sterilization campaigns on dog population size and impact as well as integrating nonsurgical fertility control with disease vaccination and public education programs.

Current and future tools for global canine rabies elimination

Even though rabies is almost uniformly fatal, it is readily preventable with currently available tools. Vaccination is highly efficacious for the pre-exposure prophylaxis (PrEP) of rabies in humans and animals, and prompt postexposure prophylaxis (PEP) with vaccine and rabies immune globulin (RIG) can reliably prevent disease in humans. However, access to these tools and knowledge of their proper use are often limited, especially in impoverished, rabies-enzootic countries with the highest disease burden. In the absence of reliable diagnostic capacity and risk assessments, vaccines and RIG are often administered inappropriately, leading to chronic supply shortages and otherwise preventable deaths. Rather than focusing solely on human prophylaxis, it is more cost-effective over the long term to eliminate canine rabies in its natural terrestrial reservoirs. Because more than 99% of human rabies deaths result from dog bites, prevention efforts should focus on dogs. A versatile "One Health" strategy for canine rabies elimination should aim to create sustainable herd immunity in dogs, using proven vaccination strategies at the local level, coupled with community education and humane population management. Such strategies have succeeded in both developed and developing countries, and can be adapted to any locality. Numerous examples in Africa, Asia, and Latin America have shown that community-based, locally guided vaccination and education programs, based on a shared vision and long-term commitment, can eliminate canine rabies. Such programs should have specific goals and measurable outcomes, and should be conducted under the guidance of supportive governments, in collaboration with international partners and nongovernmental organizations. In addition to currently available tools, rabies prevention can be augmented by new dose-sparing human vaccine schedules, alternative routes of vaccine administration, monoclonal antibodies as an alternative to RIG, sensitive and specific point-of-care diagnostics and the development of canine immunocontraceptive methods. Accurate risk assessments of potential human exposures and support for decentralized laboratory capacity will be essential to ensure the most effective utilization of vaccines and RIG until canine rabies has been eliminated.

Restart of steroidogenesis in dogs during recrudescence of testicular function following downregulation with a GnRH-agonist implant

To date, no details are available concerning the restart of steroidogenesis following the downregulation of testicular endocrine and germinative function by gonadotrophin-releasing hormone (GnRH)-agonist implants. This restart was assessed by determining the expression of steroidogenic acute regulatory (StAR) protein, cytochrome P450 side-chain cleavage enzyme (P450scc) and cytochrome P450 17α-hydroxylase,17,20-lyase (P450c17). The re-establishment of steroidogenesis was initiated by the removal of the GnRH-agonist implant (18.5 mg azagly nafarelin, Gonazon) at 5 months after treatment. Testes were removed at 3-week intervals (weeks 0-24) and four groups were formed according to the stage of spermatogenesis as revealed by the most developed germ cells observed (developmental group [DG] spermatocytes to DG elongated spermatids). Five dogs served as untreated controls. Positive immunostaining for StAR, P450scc and P450c17 was restricted to Leydig cells. Western blot indicated the specifity of the respective antibodies with hints of a expression of canine-specific P450scc and P450c17 proteins. A significant effect of group was observed for a percentage of the immunopositive area (PIA) as an indicator of active Leydig cells for StAR (P<0.05), P450scc (P<0.001) and P450c17 (P<0.001), with PIA being lowest for the DG spermatocytes. With regard to the strength of the immunopositive signal, a significant effect of group was found for P450scc (P<0.01) and P450c17 (P<0.05), with the lowest intensity being observed in DG spermatocytes. At the mRNA level, the upregulation from DG spermatocytes to DG round spermatids was clearly evident but was only significant for P450scc (P<0.05). Thus, downregulation affects the whole cascade of steroidogenesis, whereas withdrawal of inhibition results in a rapid restart, in part indicating a rebound phenomenon.

Development of semen quality following reversible downregulation of testicular function in male dogs with a GnRH agonist implant

Slow-release GnRH agonist implants have shown to be an effective and reversible alternative to surgical castration. Testicular function is downregulated with an arrest of spermatogenesis on the level of spermatogonia/primary spermatocytes but is fully restored after abolition of downregulation. Aim of this study was to assess the quality of ejaculates after active abolishment of downregulation by implant removal and to follow recrudescence of spermatogenesis. Five dogs - which served as their own controls - were treated with a slow-release implant containing the GnRH agonist azagly-nafarelin. Implants were removed during full downregulation (testosterone <0.1 ng/ml), and attempts to collect ejaculates started from week 4 onwards to week 29. First ejaculates could be obtained between weeks 8 and 12 with the first fully elongated spermatozoa observed in week 10. Volume, %motility and total sperm count increased and %pathomorphology decreased during the course of the study with all ejaculates being in the normal range by week 29. Our data indicate that onset of recrudescence of spermatogenesis coincides with the first testosterone increase after active abolishment of downregulation. Semen quality was fully regained with a significant improvement of %pathomorphology (p < 0.05) and a tendency of improved %motility. However, these observations on an improved semen quality need further validation and no final conclusions can be drawn yet.

Hormonal and antimicrobial therapy in theriogenology practice: currently approved drugs in the USA and possible future directions

Hormonal and antimicrobial therapies are essential to regulate and maintain healthy reproduction in domestic animals. The appropriate and legal use of these compounds is ultimately the responsibility of the veterinarian and other users, with a primary mission to directly protect and promote the health of animals, and indirectly the health of people. The appropriate use of these products is defined by the Federal Food, Drug, and Cosmetic Act, 21 United States of America § 301 et seq and implementing regulations in the Code of Federal Regulations. In the past, use of a drug in an animal for an unapproved use violated this Act. However, passage of the Animal Medicinal Drug Use Clarification Act 1994 legalized the extra-label use of certain animal and human drugs in veterinary practice for treating diseases. This manuscript reviews currently approved hormonal and antimicrobial drugs for use in theriogenology. Considering the ever increasing knowledge in the area of veterinary reproduction, particularly in the treatment and control of reproduction using antimicrobials and hormones, it would be beneficial to widen the therapeutic options in these categories. The potential for widening the therapeutic options is also discussed in this review, by providing a non-exhaustive but essential list of potential new drugs for use in clinical animal reproduction (theriogenology).