Delay of Puberty and Reproductive Performance in Male Dogs Following the Implantation of 4.7 and 9.4 mg GnRH-Agonist Deslorelin at an Early Pre-pubertal Age

Authors

  • S Sirivaidyapong,

    Corresponding author
    1. Innovation Center for Obstetrics, Fertility and Reproductive Disorders, Faculty of Veterinary Science, Small Animal Teaching Hospital, Chulalongkorn University, Bangkok, Thailand
    • Department of Obstetrics, Gynaecology and Reproduction, Faculty of Veterinary Science, Small Animal Teaching Hospital, Chulalongkorn University, Bangkok, Thailand
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  • NS Mehl,

    1. Department of Obstetrics, Gynaecology and Reproduction, Faculty of Veterinary Science, Small Animal Teaching Hospital, Chulalongkorn University, Bangkok, Thailand
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  • TE Trigg

    1. PT Consulting Pty Limited, Balmain, NSW, Australia
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Author's address (for correspondence): Sudson Sirivaidyapong, Department of Obstetrics, Gynaecology and Reproduction, Faculty of Veterinary Science, Small Animal Teaching Hospital, Chulalongkorn University, Bangkok 10330, Thailand. E-mail: s_sudson@yahoo.co.uk; sudson.s@chula.ac.th

Abstract

Contents

Stray dogs are a significant problem in large cities. Contraception is an important and useful solution to control the growing population of these dogs. Early-age neutering is an effective technique for canine population control; however, surgical neutering may not be possible in various situations. GnRH-agonist implantation has been successful for long-term reversible contraception in dogs. The efficacy of GnRH-agonist implantation on long-term suppression of reproductive performance was observed in male dogs. Eleven 4-month-old dogs were implanted with 4.7, 9.4 mg deslorelin or placebo. Sexual behaviour and testicular size were monitored every 2 months. Ejaculates were collected and evaluated at 8, 12, 15, 18, 24, 30, 32, 34 and 36 months of age. Dogs implanted with placebo were found to be healthy and in normal reproductive status. Most dogs (3/4) implanted with 4.7 mg deslorelin showed male sexual behaviour at age of 34 months old. From this group, two dogs had normal semen quality, while semen could not be collected from the other dog, and after castration, no sperm were obtained following epididymal flushing. One dog implanted 4.7 mg deslorelin and four dogs implanted with 9.4 mg deslorelin remained in the non-pubertal reproductive status at 30–34 months. The delay to puberty was longer in dogs implanted with higher dose of GnRH agonist. Implantation of pre-pubertal dogs with high doses of GnRH agonist will delay the onset of puberty and may be an effective strategy to reduce the number of unwanted breedings.

Introduction

Overpopulation of dogs is a major problem worldwide and leads to euthanasia of many unwanted dogs and cats. Pet overpopulation problems are frequently the result of animals not being entered into neutering programs (Stubbs et al. 1995). Contraception is the efficient method of controlling the growing population of unwanted domestic animals. Traditional contraception of females by ovariohysterectomy and progestin administration is widely used despite the risks of adverse effects. Dogs and cats bred at their first oestrus may become pregnant and deliver offspring, while they may be not mature enough physically and behaviourally nurture them (Joyce and Yates 2011). Early-age neutering is considered to be an effective technique in controlling pet overpopulation (Olson et al. 2001). However, many problems have been associated with early-age neutering of animals, including musculoskeletal, urinary tract and other systemic problems. Surgical neutering has been associated with anaesthetic concerns as pre-pubertal animals have higher sensitivity to many drugs, a limitation of hepatic function which may lead to a prolong effect of drugs and a lower capacity of compensation by the cardiovascular system (Joyce and Yates 2011). However, in a study by Howe et al. (2001), no difference in physical or behavioural problems was found between early-age and traditional gonadectomy. A new contraceptive method using a GnRH-agonist implantation (Suprelorin®; Peptech Animal Health, NSW, Australia) has been proven for use in dogs for long-term reversible contraception without negative effects to the dogs (Trigg et al. 2006). The objective of this study was to test the efficacy of GnRH-agonist implantation in early pre-pubertal male dogs on long-term suppression of their reproductive performance.

Materials and Methods

Eleven dogs (six male beagles from two litters and a litter of five mongrels) at the age of 4 months were allocated into two treatment groups and one control group by simple randomization. Group 1 consisted of two male beagles and two mongrels that were subcutaneously implanted with a 4.7 mg deslorelin into the interscapular region. Group 2 consisted of two male beagles, and two mongrels that were treated with a 9.4 mg deslorelin implant. Group 3 (Controls) consisted of three dogs from each litter that were implanted with a placebo.

Each dog was housed with a family and was examined at 8, 12, 15, 18, 24, 30, 32, 34 and 36 months of age. Sexual behavioural changes were evaluated by observations of the owners (veterinary students) and were compared with previously published normal values (Hart and Eckstein 1997) and testicular size was monitored using vernier callipers to measure maximum diameter every 2 months after the treatment. At each time point, semen collection facilitated using a teaser bitch and semen evaluation was performed (Kutzler 2005). Semen quality was considered normal or abnormal by reference to previously published data (Sirivaidyapong et al. 2000).

The growth, size, height and figure of dogs were observed by the experienced owners using breed characteristic criteria obtained from general dog breed information. Non-sexual behaviour was also observed and recorded (Hart and Eckstein 1997).

Dogs were castrated when the testicular diameter was larger than 20 mm and sexual behaviour was observed.

Following castration, the cauda epididymis was dissected from each testis. Then a small needle was inserted and sperm diluent was back flushed through the vas deferens for collection of epididymal sperm (Sirivaidyapong 2002; Ponglowhapan et al. 2006).

Results

Control group

All dogs in the control group had normal development of the testes, male behaviour and sperm quality from 12 to 15 months old (Tables 1-3).

Table 1. The sexual behaviour in 11 dogs during 8–36 months old following GnRH-agonist deslorelin implantation at 4 months old
DogDeslorelin implantAge (month)
81215182430323436
Sexual behaviour observation
  1. +: penile erection, libido, mounting or mating behaviours; −: no sexual behaviour; +/−: only mounting behaviour; n/o: no observation, dog had been neutered.

Ba-14.7 mg+n/o
Bb-14.7 mg+n/o
M-14.7 mg+n/o
M-24.7 mg+/−
Ba-29.4 mg+/−+/−
Bb-29.4 mg+/−+/−
M-39.4 mg+/−+/−
M-49.4 mg+/−+/−
Ba-3Placebo++++++++n/o
Bb-3Placebo+++++n/on/on/o
M-5Placebo++++n/on/on/on/on/o
Table 2. The size of testicles (right; R and left; L) in 11 dogs during 8–36 months old following GnRH-agonist deslorelin implantation at 4 months old
DogDeslorelin implantAge (month)
81215182430323436
Testicle scale (approximate diameter)a
RLRLRLRLRLRLRLRLRL
  1. a

    1: 10–15 mm; 2: 16–20 mm; 3: 20–25 mm; 4 > 25 mm, –: no measurement.

Ba-14.7 mg1111111111112233
Bb-14.7 mg1111111111113333
M-14.7 mg1111111111113333
M-24.7 mg111111111111111111
Ba-29.4 mg111111111111111111
Bb-29.4 mg111111111111111111
M-39.4 mg111111111111111111
M-49.4 mg111111111111111111
Ba-3Placebo2222223344444444
Bb-3Placebo222233334444
M-5Placebo22223344
Table 3. Sperm collection and quality in 11 dogs during 8–36 months old following GnRH-agonist deslorelin implantation at 4 months old
DogDeslorelin implantAge (month)
81215182430323436
Sperm collection and quality
  1. N: collectable with normal sperm quality; –: fail to collect sperm; n/o: no observation, dog had been neutered.

Ba-14.7 mgn/o
Bb-14.7 mgNn/o
M-14.7 mgNn/o
M-24.7 mg
Ba-29.4 mg
Bb-29.4 mg
M-39.4 mg
M-49.4 mg
Ba-3PlaceboNNNNNNNNn/o
Bb-3PlaceboNNNNNn/on/on/o
M-5PlaceboNNNNn/on/on/on/on/o

Group 1

Three of the four dogs implanted with 4.7 mg deslorelin began to show male sexual behaviour and their testes became well developed and had a firm consistency at two and half years post-implantation (at ages of 34 months old) (Tables 1 and 2). Semen was collected in two dogs at this time, with normal sperm characteristics (Table 3). The remaining dog showed only slightly male behaviour, very small and soft testes, very low libido (Tables 1 and 2) and failed to ejaculate. After castration and flushing of the epididymis no sperm were recovered.

There were no subjective differences of growth, size, height, conformation or non-sexual behaviour between these dogs and controls.

Group 2

All four dogs implanted with 9.4 mg showed only slightly male behaviour, very small and soft testes, very low libido (Tables 1 and 2) and no collectable semen at ages of 30–36 months.

There were no subjective differences of growth, size, height, conformation or non-sexual behaviour between these dogs and controls.

Discussion

GnRH-agonist implantation in early pre-pubertal dogs has previously been shown to be effective as a safe contraception technique by the desensitization of the pituitary gonadal axis (Trigg et al. 2006) without an up-regulation or flare up effect.

In the present study, implantation with 4.7 mg deslorelin was effective in delaying the onset of puberty for <2 years (except one implanted mongrel dog), whereas implantation with the 9.4 mg deslorelin was effective for more than 2 years. Five dogs remain under observation and are still without signs of puberty at 38 months post-implantation. The difference of the duration of the GnRH-agonist effect might be due to the differences in the implant concentration, dosage or simply individual dog variation but is most likely to be related to the duration of release of deslorelin from the 9.4 mg implant. The duration of release has been measured in vitro to be at least twice that of the smaller dose implant (T.E. Trigg personal communication)

In conclusion, the study demonstrated the long-term delay of puberty and reproductive performance in male dogs following the GnRH-agonist deslorelin implantation at 4 months old. The higher dosage showed a longer duration of pubertal postponement and administration of the implant to pre-pubertal dogs could form the basis of a strategic plan for controlling unwanted births in poorly controlled dog populations.

Acknowledgements

Innovation Center for Obstetrics, Fertility and Reproductive Disorders, Small Animal Teaching Hospital, Faculty of Veterinary Science, Chulalongkorn University. Veterinary Students who took care of all beagles, owners of other dogs and Peptech Animal Health, Australia.

Conflicts of interest

None of the authors have any conflicts of interest to declare.

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