Effect of exogenous melatonin on sexual behaviours in West African Dwarf goat

J O Daramola, A A Adeloye and A O Soladoye*

Department of Animal Production, University of Ilorin, Nigeria
*Department of Human Physiology, University of Ilorin, Nigeria
daramolajames2003@yahoo.com

Abstract

Two trials were conducted to investigate the effect of exogenous melatonin on sexual behaviours of West African Dwarf (WAD) goats. Thirty two WAD goats (20 does and 12 bucks) were used. Does were administered doses of melatonin at 0,3,6 and 9mg. In the second trial, bucks were administered doses of melatonin at 0,3,6 and 9mg. Melatonin was administered orally for ten consecutive days.

Oestrus response (P<0.05) was 40, 60, 100 and 80% for the 0, 3, 6, and 9mg melatonin respectively. Does induced with 6mg melatonin had shorter interval (22.0 ± 0.22 days) between treatment termination and onset of oestrus compared to 0 (24.5± 0.5 days), 3 (25.0±0.98 days), and 9mg melatonin (23.5 ± 0.74 days). Similarly, does induced with 6mg melatonin had longer duration of oestrus (58.6±1.49 hrs) compared to 0 (54.0 ± 1.19 hrs), 3 (55.0 ± 0.99 hrs) and 9mg melatonin (58.0 ±1.16hrs). In addition, does induced with 6mg melatonin had higher (P<0.05) serum oestrogen concentration (25.36± 11.46 pg/ml) compared to 6.98± 4.93 pg/ml, 23.77± 6.77 pg/ml and 16.94± 0.89 pg/ml for 0, 3 and 9mg melatonin respectively. Sexual behaviours of bucks showed increased (P<0.05) full erection with 6mg melatonin (2.0+0.4) compared to 0 (0.66+0.2), 3 (1.66+0.28) and 9mg melatonin (1.33+0.2).

The findings of this study indicate that treatment of WAD does with 6mg melatonin resulted in a two and half-fold increase in the does that came on heat. Similarly, treatment of bucks with 6mg melatonin improved sexual behaviour in WAD bucks.

Keywords: Exogenous melatonin, goat, sexual behaviours

Introduction

Considerable information is available on the reproductive functions and characteristics of West African Dwarf goats (Orji 1985, Okere 1983, Ugwu and Orji 1984). Study on reproductive management and simple technique of improving reproductive efficiency of this breed is however limited. One of the difficulties associated with operating an animal breeding enterprise is that almost everything relating to actual mating must be done when the female is ready, rather than at the farmer's discretion. Thus, there has been considerable interest to manipulate ovarian activity so that ovulation is regulated to allow mating at predetermined times. At present, no technique precisely regulates ovulation but reasonably effective pharmacological and physical methods are available to synchronize oestrus in mature cyclic females or to stimulate follicular phases in near puberty or a cyclic animal. (Faure et al 1983, Asher et al 1993, Baril et al 2000, Greyling and Van Der Nest 2000).

Melatonin is a hormone secreted by the pineal gland (Bittman et al 1983) and has been reported to stimulate the onset of reproductive activity by stimulating gonadotrophin release (Haresign et al 1990). This hormone has an effect on luteinizing hormone, testosterone, testis activity and puberty in small ruminants (Asher et al 1993). Sexual preparation prior to ejaculation has been reported to increase the sperm output (Hale and Almquist 1970). There is therefore cause to attempt to stimulate sperm production using less expensive preparations with the aim to ensuring high conception rates in both naturally mated and artificially inseminated does. The objective of this study was to determine the effect of exogenous melatonin on sexual behaviour in West African Dwarf goats.

Materials and methods

Two trials were conducted which involved thirty two West African Dwarf (WAD) goats (20 does and 12 bucks) at the University of Ilorin Teaching and Research Farm. The animals were fed concentrate (500g/animal) consisting of maize (30%), groundnut cake (10%), wheat offals (32%), palm kernel cake (25%), bone meal (2%), salt (0.5%), and vitamin/mineral premix (0.5%) and grasses consisting of Guinea grass (Panicum maximum) and Elephant grass (Pennisetum purpureum). They were dewormed and had access to fresh water ad libitum.

In the first trial, twenty non-pregnant and non lactating adult West African Dwarf does selected from a flock of twenty seven does, aged 2-3years, 1-2 parity and weighed 15.80 + 2.28, were housed as a group in a pen fenced with open space. The animals were randomly divided into 4 treatment groups. The treatment groups consisted of animals receiving 0mg melatonin (control), 3mg melatonin, 6mg melatonin, and 9mg melatonin. Each treatment group was given different oral dose of melatonin for 10 consecutive days. Following termination of treatment, the animals were observed for signs of oestrus. Two mature bucks were used twice daily (9am and 6pm) for oestrus detection. The bucks were quickly separated from the does as soon as sexual receptivities were exhibited to avoid mating. All does showing oestrus after treatment were noted for onset of oestrus (days) and duration of oestrus (hours).

In the second trial, twelve West African Dwarf bucks, 11.5+1.85months old with body weight of 12+1.75 kg were kept separate from the does. The bucks were randomly divided into 4 treatment groups. The treatment groups consisted of animals receiving 0mg melatonin (control), 3mg melatonin, 6mg melatonin, and 9mg melatonin administered for 10 days via oral route. The bucks were introduced into the pen containing 20 does (where 14 of the does had earlier been induced into oestrus) for 30 minutes to observe sexual behaviour. Manifestation of sexual behaviour was observed and recorded. Sexual behaviour observed as time expressed "interest" in doe. "Interest" was classified as full erection; attempt to mount without erection; and no interest. The buck was separated from the does as soon as sexual receptivity was observed to avoid mating. The procedure was repeated twice daily for 3 days of oestrus period.

Blood sampling

Upon detection of oestrus in does, blood samples were collected daily over a period of 3 days and in bucks weekly following termination of treatment through jugular vein. The blood samples were collected into plastic tubes and allowed to clot at room temperature. Serum was separated by centrifuging within 3 hours of collection and stored at -20^oC for hormonal assay. Progesterone was determined by Enzyme Immunoassay (EIA) method using Progesterone Enzyme Immunoassay test kit catalog number 2077Z from Diagnostic Automation Inc. 23961 Craftsman Road, Suite E/F Calabasas, CA91302. Oestrogen was determined by EIA method using Estradiol Enzyme Immunoassay test kit catalog number 2046Z. Testosterone was determined by EIA method using Testosterone Enzyme Immunoassay test kit, catalog number 20952 from the same source.

Statistical Analysis

Data were analyzed using two-way ANOVA in Completely Randomized Block Design and Duncan Multiple Range Test (Duncan 1955) was used to rank means of treatment in a COSTAT programme.

Results

The response of does to different levels of melatonin treatment is shown in Table 1.

Following the administration of melatonin, 2 of 5 (40%) does showed oestrus in the 0mg melatonin, 3 of 5 (60%) does showed oestrus in the 3mg melatonin group, all the 5 (100%) does responded in 6mg melatonin group and 4 of 5 (80%) does responded in 9mg melatonin group. There were significant differences (P<0.05) in oestrus responses between treatments. The study indicated that the dose of melatonin affected the exhibition of oestrus. The mean interval from termination of treatments to first signs of oestrus (onset of oestrus) was statistically significant between treatment groups. There was also statistical difference on the duration of the induced oestrus. The lower dose (3mg) of melatonin prolonged the onset of oestrus while 6mg prolonged the duration of oestrus.

The serum progesterone and oestrogen levels during the induced oestrus period are presented in Table 1. The results showed differences between oestrogen levels among the treatment groups (P<0.05). There were differences between the days of induced oestrus periods in the hormone levels (Figure1).

Following the onset of oestrus, mean serum oestrogen concentration rose from day1 of oestrus to a maximun of 34.0.43 +11.61pg/ml on day2 of the oestrus (P<0.05). Serum oestrogen concentration declined by day3 and reached a low level of 16+12 .7pg/ml.

The sexual behaviours observed during the three days when the bucks were introduced into oestrus induced does differed significantly between the levels of melatonin (Table1). The manifestation of sexual behaviours (Figure 2) as evidenced by interest in mating through mounting and erection was greater in bucks treated with various levels of melatonin compared with the control. Instances of full erection were higher in bucks treated with 6mg (P<0.05).

 Serum testosterone rose sharply following treatment with 6mg melatonin starting from the beginning of the experiment compared with other treatment groups (Figure 3).

Discussion

The observed effect of the different doses of melatonin on oestrus confirms the efficacy of melatonin to synchronize oestrus, a process Chemineau et al (1996) described as a prerequisite for Artificial Insemination. In the present study, appreciable numbers of does were in oestrus following a ten days melatonin treatment. This study however differs from the reports of Faure et al (1983), Walker et al (1989), Crosby et al (1991) and Greyling et al (1994, 1997) who did not find any difference in oestrus response for different types and doses of synchronizing agent such as progestagen. Perhaps, the drug, breed of animal, season of the year and agroclimatic region contributed to the variation in synchronization response reported in the various studies.

This study indicates that 6mg melatonin was more efficient in synchronizing oestrus in WAD does and the dose was needed for efficient feedback on the hypothalamus (Greyling et al 1997). The findings of this study support an earlier study of Fiske et al (1984) which showed that melatonin alone could stimulate steriodogenesis by direct action on the ovary. Greyling et al (1994) reported that doses of progesterone exerted no effect on the oestrus response time in ewes synchronized outside breeding season. However, Faure et al (1983) and Greyling et al (1997) obtained shorter time intervals between treatment-termination to onset of oestrus. The time period between the termination of melatonin treatment and onset of oestrus is far higher to an interval of 30.5h between cessation of progestagen treatment, and the onset of oestrus reported by Greyling et al (1997) and 32.2h reported by Motlomelo et al (2002). Though the difference may be explained by differences in breed, drug, nutrition and season which are known to influence this parameter (Ahmed et al 1998), the slow effect of melatonin could account for the longer interval of onset of oestrus as melatonin has been reported to induce a slower luteolysis (Noel et al 1999). This delay in the onset of oestrus behaviour has been reported to be associated with a delay in the LH preovulatory surge (Maurel et al 1992) and a delay in the time of ovulation (Leboeuf et al 1993). Moreover, the difference observed in the duration of oestrus between melatonin-induced oestrus does and the control agreed with these workers.

Variation between treatments regarding duration of oestrus might be due to the amount of oestrogen in the blood arising from induced luteolysis as oestrogen level in the blood is presumed to bring the animals in oestrus and a depressing effect on progesterone (Mirskaria et al 1941, Noel et al 1999). As such, it appeared that high levels of serum oestrogen concentrations might be responsible for the prolonged duration of oestrus observed in the melatonin-induced does. Oestrogen secretions were higher and could probably be due to follicular phase of the synchronized oestrus cycle in doses treated with melatonin (Fiske et al 1984), the physiological stage characterized by behavioural oestrus.

There were variations of sexual behaviours between the treatment groups. The manifestation of sexual behaviours as evidenced by interest in mating through mounting and erection was greater in buck treated with various levels of melatonin compared with the control. Previous studies have demonstrated that melatonin induced sexual activity in seasonally inactive male goats (Chemineau et al 1992). Sexual preparation prior to mating or ejaculation has been reported to increase the sperm output (Hale and Almquist 1970). The results showed that bucks treated with melatonin were more active in sexual behaviours and melatonin treatment could be an effective technique for enhancing sexual activity in WAD bucks and administration of 6mg melatonin daily in ten days was effective to improve sexual behaviour in WAD bucks. The observation that the sexual behaviour declined in the treatment group that received a higher dose of melatonin suggested that a high dose rate such as the 9mg melatonin per buck per day for 10 days given in this study could produce suppressive effect on the hypothalamus. A negative feedback may have been established that worked for further decrease in testosterone levels, which in turn reduced the sexual behaviour.

Conclusions

• This study has attempted to stimulate the onset of sexual activities using exogenous melatonin with the aim of ensuring high conception rates in both naturally mated and artificially inseminated WAD does.

• A dose of 6mg melatonin during ten days treatment was effective to enhance sexual behaviours in West African Dwarf does and bucks.

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Received 25 April 2006; Accepted 25 July 2006; Published 14 September 2006

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