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2010, Vol. 5 No. 1, Article 56

 

Induction of Fertile Oestrus in Dogs Using Cabergoline

G. Ajitkumar*1 and R. Praseeda2

 

1Post-doctoral Fellow, 2PhD Scholar

Department of Production Animal Health
Faculty of Veterinary Medicine
University of Calgary, Calgary, Canada

 

*Corresponding Author; e-mail address: ajitvet@yahoo.co.in

 


ABSTRACT

The effect of oral administration of cabergoline, an anti-prolactin drug on induction of fertile oestrus in bitches belonging to different breeds and age groups is placed on record. Anoestrus bitches (n=20) were treated with cabergoline @ 5g/kg. body weight orally for 20 consecutive days, 80% (n=16) responded to the treatment by evincing proestrual bleeding and the mean time taken from treatment onset to proestrus was found to be 13.44 3.12 days. The duration of proestrus and oestrus was found to be 10.11 0.68 (range, 8 to 12) and 8 0.29 (range, 6 to 9) days respectively. The conception rate in relation to the number of bitches responding to the oestrus induction treatment was 87.50% (14 out of 16) and the overall conception rate in relation to the number of animals subjected to oestrus induction trial was 70% (14 out of 20).

KEY WORDS

Oestrus, conception, bitch, cabergoline.

INTRODUCTION

The reproductive physiology of domestic bitches is unique that they exhibit cyclicity only once or twice in a year (Verstegen et al., 1999). The length of oestrous cycle in the bitch is considerably longer than that of most other domestic species and there is an obligatory anoestrus following the termination of the luteal phase (Verstegen et al., 1999). The anoestrus could be primary (the bitch that never had an ovarian cycle) or secondary (the bitch that had one or more ovarian cycles but subsequently failed to cycle) (Feldman and Nelson, 1996). Even though dogs are reared primarily as companion, pet and guard, currently many have identified the potential of dog breeding units as a remunerative vocation. Since timely reproduction has got paramount importance in optimizing the return from dog breeding units, owners of elite bitches with long inter-oestrus interval often approach veterinarians with the request to shorten it in order to increase the number of litters born per year. Perusal of literature revealed the use of a variety of exogenous hormones and their combinations viz., GnRH, FSH/LH, eCG/hCG and oestrogens for induction of oestrus in bitches with varying results (Vanderlip et al., 1987, Shille et al., 1984, Concannon, 1992 and Bouchard et al., 1993). Administration protocols of most of these drugs involved daily to weekly injections and the results were not encouraging. Here comes the importance of newer drugs with better oestrus induction and conception rates.
Prolactin appears to play a role in canine interoestrus interval, possibly by affecting gonadotrophin secretion and/or ovarian responsiveness to gonadotrophins. Suppression of prolactin secretion by administration of dopamine agonists shortened the duration of anoestrus (Van Haaften et al., 1989) or induced oestrus in cases of prolonged anoestrus (Jochle et al., 1987; Arbeiter et al., 1988 and Kutzler, 2007). Harvey et al. (1999) reported remission of signs of pseudopregnancy in bitches by the administration of cabergoline, a dopamine agonist. It was reported to be effective in shortening the length of anoestrus period of Beagle bitches also (Phillips et al., 2003).
Onclin and Verstegen (1997) demonstrated that the effects of cabergoline on termination of anoestrus were mediated through prolactin and not directly through corpus luteum thus confirming the indirect mode of action of dopamine agonists on corpus luteum. According to Spattini et al. (2007), the increase in mean plasma concentration of LH noticed without an effect on plasma prolactin level on administration of cabergoline at the rate of 5μg/kg body weight in anoestrous bitches supported the observation of Olson et al. (1982), Kooistra et al. (1999) and Okkens and Kooistra (2006) that in the bitch the induction of follicular development was not initiated by the suppression of prolactin secretion but by other direct or indirect dopaminergic effects on the hypothalamo-hypophyseal-ovarian axis. Harvey et al. (1997) opined that cabergoline had a more specific action on D2 dopamine receptors of the anterior pituitary gland and therefore had a greater activity and long lasting effect than bromocriptine. Kutzler (2005) reported that cabergoline was found to be a more specific dopamine agonist than bromocriptine and had a longer duration of action and produced fewer side effects than bromocriptine. Under these circumstances, a study was undertaken to assess the efficacy of oral administration of prolactin antagonist, cabergoline in inducing fertile oestrus in anoestrous bitches.

MATERIALS AND METHODS

Healthy bitches presented at University Veterinary Hospital, Kokkalai, Thrissur, Kerala with the complaint of anoestrus formed the material for the present trial. In order to confirm anoestrus, they were subjected to exfoliative vaginal cytology (Feldman and Nelson, 1996) and estimation of serum progesterone level. From among them healthy bitches (n=20) belonging to different breeds and age ranging from 2 to 5 years, with serum progesterone level less than 1 ng/ml were selected and subjected to oestrus induction trials using cabergoline @ 5 mg/kg body weight once daily orally for 20 consecutive days. The bitches (n=16) which responded to the treatment by evincing proestrual bleeding were subjected to exfoliative vaginal cytology to identify the best time for breeding based on anuclear cell index (Feldman and Nelson, 1996). They were bred with apparently healthy, fertile male dogs first when the anuclear cell index was >80% and subsequently at 72 h interval till the end of oestrus. They were further subjected to ultrasound scanning and abdominal palpation for pregnancy diagnosis between day 20 & 25 and 30 & 35 post-breeding respectively and those found pregnant were followed up till whelping and the gestational length and litter size recorded.

RESULTS AND DISCUSSION

Out of the 20 anoestrus bitches treated with cabergoline for induction of oestrus, 16 (80%) responded to the treatment by evincing proestrual bleeding. The proestrus response obtained in the present study was found to be lower than that of an earlier trial in which Verstegen et al. (1999) could obtain a proestrus response of 93.33 per cent in bitches treated with cabergoline. This might be due to the fact that the bitches involved in this trial were belonging to different breeds and age groups. Among the animals responding to the treatment, the mean time taken from treatment onset to proestrus was found to be 13.44 3.12 days. Van Haaften et al. (1989) reported a mean treatment onset to proestrus of 28 days in bitches treated with bromocriptine. It was reported to be 29.75 5 days (Jeukenne and Verstegen, 1997), 16 days (Gobello et al., 2002) and 23.63 14.33 days (Cirit et al., 2007) on inducing oestrus with cabergoline. Hence, the mean time taken from treatment onset to proestrus in the present study was found to be less than that in the earlier reports. The average duration of proestrus and oestrus was found to be 10.11 0.68 and 8 0.29 days respectively. The duration of proestrus and oestrus obtained in the present study is in agreement with that of the earlier reports based on cytology (Jeukenne and Verstegen, 1997; Verstegen et al., 1999; Gobello et al., 2004).
The conception rate obtained in the present study in relation to the number of bitches responding to the oestrus induction treatment was 77.78 per cent (14 out of 16) and the overall conception rate in relation to the number of animals subjected to oestrus induction trial was 70 per cent (14 out of 20). Rota et al. (2003) and Gobello et al. (2004) reported a conception rate of 83 and 82.60 per cent on inducing oestrus in bitches using cabergoline. The mean gestation length calculated from the last breeding date and the litter size were 62.23 2.33 days and 6.25 1.89 respectively. The findings of the present trial revealed that the anti-prolactin drug, cabergoline @ 5 g/kg. body weight once daily orally for a period of two weeks could be used for the successful induction of oestrus with satisfactory conception rate in anoestrus bitches of different breeds and age groups.

ACKNOWLEDGEMENT

Thanks are due to the Professor and Head, University Veterinary Hospital, Kokkalai, Thrissur for the facilities provided and the Dean, College of Veterinary and Animal Sciences, Mannuthy, Thrissur for granting permission to publish this paper.

REFERENCES

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