Page 574 - WSAVA2018
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 25-28 September, 2018 | Singapore
increased sample to adult levels prior to implantation, penile spikes and masculine behavior were not present at study onset and never appeared until puberty which occurred in the 3 toms at an age of 19-22 months1. Although detailed information on onset of susceptibility to exogenous GnRH around the time of puberty is not available for dogs and cats, use of GnRH agonists can probably be regarded as a reasonably safe method to postpone puberty in cats; more data are necessary in tomcats to draw the same conclusion (although a similar effect is likely to occur).
Suppressing cyclicity in adult queens
In adult queens administration of a 4.7 mg deslorelin implant initially stimulates follicular growth and oestradiol secretion, after which no further evidence of estrus is observed for periods of 4-14 months 6 or up to 16-37 months7,8. The initial stimulation of follicular growth may lead to a true heat in a small percentage of implanted queens. Small estrogen increases have been observed in 50% of treated queens 5-14 months after treatment6,8. Deslorelin-treated queens may ovulate if bred early
in the follicular phase 8; progesterone increased significantly in all queens treated in the follicular phase until day 14 after treatment, then slowly decreased reaching basal level on day 56 post-treatment: duration of this luteal phase could be regarded as comparable to the normal, non-pregnant feline luteal phase8. Incidence of spontaneous ovulation at the induced heat and incidence of premature luteal failure at the induced pregnancy are unknown. More studies are needed on post-treatment luteal function in queens administered a deslorelin implant. General health and social behaviour have never shown any deviation from normality, and introduction of a male is not capable of reversing the deslorelin-induced cycle suppression6.
The 9.4 deslorelin implant is characterized by a longer action in queens. We looked at duration of effect of the 9.4 deslorelin implant in 15 adult (6 months- 5yrs of age) queens. Based on vaginal cytology and serum P4 data induction of heat was observed in 40% of queens during the first month post-implantation. Subsequently, the first post-tretment heat was observed in 15% of queens after day 600, and by post-treatment day 720, 800 and 1090 percentages of queens in heat were 50%, 70% and 100%, respectively (unpublished data).
Inducing oestrus in adult queens
Because of the high fertility of cats, estrus induction in queens is an unusual request to veterinarians except for wild felids in captivity which may be object of germ cell conservation programs. Historically, estrus induction in cats has been performed for decades using variable protocols with Pregnant Mare Serum Gonadotropins which is however characterized by excessive ovarian stimulation and sometimes equivocal results. The
occurrence of signs of heat has been repeatedly observed when treating adult queens with 4.7 or 9.4 mg deslorelin implants, albeit not in all queens and not with the same intensity. We observed signs of heat (vaginal epithelial keratinization, and in some females also vocalization or crouching) in 19/20 treated queens 3-4 days after treatment with the 4.7 mg deslorelin implant (queens were implanted irrespective of oestrous cycle stage)7. In another study oestrus induction was observed in 2/20 queens when a 4.7 mg deslorlein implant was administered during the follicular phase or immediately post-estrus8. Recently, Zambelli et al. 11 treated 13 adult queens with a 4.7 mg deslorelin implant: all queens showed vaginal epithelial keratinization, and 7/13 queens showed behavioural signs of heat11; three of these 7 queens were artificially inseminated and gave birth to normal litters9. In our 9.4 mg deslorelin study 40% of queens showed vaginal epithelial or behavioural signs of heat during the first month post-treatment (unpublished data). Deslorelin may be used to induce oestrus in adult queens. The induced oestrus is normal and fertile. As the cat is a seasonal breeder, time of the year may play a role in oestrus induction response to deslorelin.
Controlling fertility and reproductive behaviour in males
In adult tomcats, a 4.7 mg deslorelin implant is able to suppress the HPG axis leading to disappearance of serum testosterone and male urine odour. Following treatment, serum testosterone drops significantly to undetectable levels already during the second week post-treatment and does not start rising again often for one year or longer; penile spikes start disappearing at 60 days and are absent by 90 days; testicular volume decreases reaching <2/3 of normal volume by 7-8 months; also, food intake and body weight tend to increase in implanted cats, who often gain 10-20% of their initial body weight in about 6 months10. From a reproductive behaviour standpoint, roaming and mating behaviour decrease within 2 months and there is an improvement in friendliness towards humans in a high percentage of treated cats. Similarly to queens, the 9.4 deslorelin implant has a longer action in tomcats. When16 adult tomcats were implanted with the 9.4 formulation the average interval to resumption was 805 (range 750 to 850) days12.
Deslorelin can be considered as a safe alternative to surgical castration in tomcats as it prevents them from displaying all unwanted effects of gonadal steroid secretion. However it should be underlined that – unlike in dogs – not all cats respond to deslorelin. Out of approximately 45 tomcats implanted with either the 4.7 mg or 9.4 mg deslorelin we have observed 4 cases of tomcats becoming friendlier and more affectionate with humans and other cats as well but continuing
to impregnate queens for the entire duration of the

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