|Livestock Research for Rural Development 25 (8) 2013
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Citation of this paper
Sexual receptivity and fecundity were determined in rabbit does with different exposure to the male. Forty heterogeneous, mature and non-lactating does were assigned to four treatments including: VTC – Male exposure with visual and tactile contact; VIC - Male exposure with visual contact; NVC – Male exposure without visual contact and NOC - Complete isolation of does from bucks (control group). The does were maintained in this condition for 30 days after which they were hand mated, each to two bucks. Mating was assisted or forced where it didn’t occur spontaneously. At mating the sexual behaviour, readiness and libido of the does were recorded. At parturition, fertility and prolificacy were determined.
Sexual receptivity measured by behavioural attitude and rate of spontaneous mating were higher in the VTC and NVC exposed group. Mating time was also significantly reduced in these groups. Prolificacy and fertility index were both lowered in the NOC and VTC does compared to the NVC and VIC does. In conclusion results from this study indicated that the presence of the male improved the sexual receptivity of the doe. However prolonged visual and/or tactile contacts between the opposite sex appeared to be detrimental to the breeding efficiency and overall productivity of the doe.
Keywords: male presence, rabbit doe fertility
Rabbit farms in the developing countries still employ the natural mating system in their breeding operations and many maintain a buck population of 1:5-10. Thus the influence of the “buck presence” on the doe’s performance cannot be overlooked. The “buck presence” is intended here to represent the continuous exchange of anyone or combinations of visual, auditory, olfactory and tactile contacts between the male and female as different from the conventional “buck effect” which refers to the combination of visual, auditory, olfactory and tactile contact between female and male, after a period of separation. Berepudo et al (1993) were the first to report that the presence of rabbit bucks in the vicinity affect the fertility of the doe. The “buck effect” is known to be effective in stimulating and synchronizing oestrus in many farm animals (Rowlinson and Bryant 1974; Oldham et al 1978; Chemineau 1987). A number of reports have also indicated that the buck effect benefit fertility in nulliparous but not the lactating rabbit does (Lefèvre et al 1976; Kustos et al 2000; Eiben et al 2001; Bonanno et al 2003). Some authors suggest that rabbits exchange sex pheromones of either male or female origin to influence reproductive behavior in the opposite sex (Frank 1966; Vodermayer 1989; Hudson and Distel 1990; McNitt 1992). However the precise nature of the pheromones remains to be elucidated till date.
One of the main concern in rabbit reproduction today is the incidences of spontaneous ovulation in rabbit does that are neither mated nor hormonally stimulated to ovulate (Boiti et al 1996; Theau-Clément et al 2000), which normally result in pseudo-pregnancy and consequent reduction of fertility and productivity. The cause(s) of pseudopregnancy in rabbit still remain shroudy. In a recent study Ola and Oyegbade (2012) reported that does exposed to visual contact with the buck (in conjunction with olfactory and auditory contacts) showed reddish or pinkish vulva most of the time, an indication of high state of sexual receptivity. In addition corpora lutea were observed on the ovarian sections from such does which was absent in does with no visual exposure to the male. It was concluded that some male cues other than mating may also provoke ovulation in the female rabbit.
In the present study we determined the effect of the “buck presence” on mating receptivity and fecundity in non-lactating rabbit does. This study is of practical relevance to rabbit production in the developing countries in which males are permanently housed in the vicinity of the females.
Forty does and fifteen bucks of heterogenous breed housed in individual cages at the Obafemi Awolowo University Teaching and Research Farm (7° 28’N; 4° 33’E; 240 m above sea level) were used for this study. The does were not lactating but varied in parity from 1 - 4 and body weight from 1565 – 2210 g at the commencement of the experiment. The bucks weighing between 2200 – 2800 g were all intact and of proven fertility. The animals were exposed to the prevailing 12:12 light:dark hour cycle and offered 60 g/animal/day (about 3 % of body weight) of compounded diet containing 2400 kcal digestible energy/kg DM and 18 % of crude rotein as well as ad libitum mixture of Panicum maximum and Moringa oleifera foliages. Water was also supplied ad libitum.
The experiment was a completely randomized design. Four different exposure treatments were tested and the possible contact between the bucks and the does under each treatment are shown in Table 1 below.
The does were randomised on the basis of body
weight into the 4 treatments namely:
VTC – Male exposure with visual and tactile contact;
VIC - Male exposure with visual contact;
NVC – Male exposure without visual contact and;
NOC - Complete isolation of does from bucks (control group).
Animals in the VTC, VIC and NVC groups were housed with a buck in a separate cage in between two does. In the VTC group aproned buck was introduced into each doe for 5 minutes between the hours of 10:00 – 11:00 hr daily with close supervision. During this period the buck attempted to mate with the doe but was unsuccessful because of the apron in place. In the NVC group, visual contact between the male and female pair was blocked with a solid dark partition. Does in the NOC group were housed without male, in another building about 200 m away. Animals were maintained in this condition for 30 d and then randomly bred on the 31st and 32nd day.
All does were individually hand mated by transferring the females to the male cage and returned back to their treatment cages immediately after mating. Where spontaneous mating did not occur within 5 minutes of pairing, mating was assisted by tying the tail of the doe upward to expose the vulva and if necessary doe was force mated by holding the doe down for the buck to mount and mate. Each doe was mated to two different bucks to increase the chances for conception. Sexual receptivity of the doe was measured during the mating process by observing the behavior of the doe and its readiness to mate.
Behavioural attitude of the does monitored includes: aggressiveness toward the male; flattening to a corner of the cage; circling within the cage; allowing mounting but no lordosis posture; and allowing mounting with a lordosis posture. The time interval between the introduction of the female into the male cage and the actual mating (i.e. Libido) was noted with a stop clock. In determining this parameter the pair was first allowed full 5 minutes for spontaneous copulation in the absence of which mating was assisted or forced as described above within additional 5 minutes. Mating readiness or Acceptance rate was scored as a variable of Bernoulli: Refusal to mate and assisted or forced mating = 0; spontaneous mating with or without lordosis posture = 1.
The does were thereafter monitored throughout pregnancy. Abdominal palpation was done on the 15th day post mating but non pregnant does were not remated. At delivery litter size and weight were recorded. Fertility index was calculated as the product of litter size and kindling rate. Data recorded as percentage of occurrence were statistically compared by chi-square procedure, while the means of absolute data were compared by Analysis of Variance and Duncan test using GenStat 3 package.
The instantaneous behavior of the rabbit doe when presented to an intact buck could give a very good indication of her sexual receptivity. Aggressiveness, flattening and circling are behaviours indicative of a doe unwilling to mate. The first two behaviors were generally noticed in less than 20 % of the does in each exposure treatments, while 30 and 40 % of VIC and NOC does exhibited the circling behaviour. On the opposite, does that allow mounting by buck either with or without a lordosis posture are considered to be in oestrus condition and readily willing to mate. Mounting with lordosis was displayed by over 50 % of does with exposure to the buck (VTC, VIC and NVC does) compared to only 20 % of does excluded from buck influence (NOC). However additional 40 % of the does with no exposure to the buck accepted mounting without lordosis posture. Lordosis posture is well associated with spontaneous mating as reflected in Figure 2 although many of the non exposed does with lower occurrence of lordosis also mated spontaneously. However the exposed does mated in shorter time interval of introduction to the buck (Table 2).
|Figure 1: Behavioural attributes of rabbit does at different contact levels with the male
|VTC, visual and tactile contact; VIC, visual contact; NVC, no visual contact; NOC, no contact with male
abc – Bars in the same grouping with different letter differ significantly, P < 0.05
|Figure 2: Sexual receptivity performance of rabbit does at different contact levels with the male
VTC, visual and tactile contact; VIC, visual
contact; NVC, no visual contact; NOC, no contact with male
Sexual receptivity in rabbit does have generally been based on the colour and turgidity of the vulva (IRRG 2005; Theau-Clément 2007). We previously reported that does with prior contact with the buck displayed reddish (oestrus) vulva most the time (Ola and Oyegbade 2012) but the does were not actually tested for mating response. Here we have further evidence that exposure to the buck actually favour sexual receptivity in the doe. Lordosis posture usually facilitates spontaneous mating but does without lordosis posture also accepted mating usually after some persuasion from the buck. As would be expected the groups (VTC and NVC) with higher incidence of spontaneous mating also had shorter mating intervals. Forty percent of the does excluded from male or with only visual contact were assisted or forced to mate which led to longer copulation interval. Our result corroborated that of Berepudo et al (1993) who also reported higher frequency and intensity of oestrus in does exposed to male presence.
In our study, olfactory and auditory contact between the does and bucks in the three exposed groups were assumed to be present and thus emphasis was on the visual contact. The tactile contact in the VTC group is not a usual practice under farm production but was included as a factor to determine its possible effects. Many previous workers had favoured the existence of pheromonal (olfactory) exchange between rabbit sexes (Frank 1966; Vodermayer 1989; Hudson and Distel 1990; McNitt 1992), with no indication of any role for auditory and visual cues. Our results seem to be suggesting significant role for visual (probably in conjunction with olfactory and auditory) cue from the male in influencing oestrus in the rabbit does.
The results of the forty breedings as measured on the day of parturition are summarized in Table 3. Fertility rate was reduced in does that had daily tactile stimulation (including mounting and copulatory thrust but no coitus) from aproned bucks compared to other does. The lower fertility in the VTC group could be due to higher incidence of pseudopregnancy (although not confirmed) since these does had been mounted severally for 30 days. Both Hammond (1925) and Templeton (1940) reported that ovulation occurred in about 30 % of oestrus does after mere mounting by buck without coitus. Much later Staple (1967) also supported with claims that ovulation did occur among submissive oestrus does if they were repeatedly mounted by oestrus or anoestrus does while caged in pairs for periods ranging from 1 to 17 days.
Even though fertility rate in the male secluded does (NOC) was comparable to those with (VIC) or without (NVC) visual stimulation from buck, the prolificacy (mean litter size) was significantly lower in the NOC does. Prolificacy was likewise lower in the does that received daily male tactile stimulation. The reduced prolificacy in the male secluded group could be attributed to lower receptivity and higher incidence (40 %) of forced mating, which is in agreement with the well known connection between receptivity and fertility. Earlier reports affirmed that ovulation and fertility rates were reduced when non receptive does were force mated (Templeton 1940; Foote et al 1963; Theau and Roustan 1980; Battaglini et al 1986). The higher kit birth weight observed in the male secluded does could readily be linked to the lower litter number and the incidence of still birth in this group.
Taking the receptivity and kindling performance together, the results indicated that the fecundity of the does could be negatively affected after continuous exposure to male presence. Although previous authors on buck effect on rabbit fertility agreed that it benefited the primiparous but not lactating does (Kustos et al 2000; Eiben et al 2001; Bonanno et al 2003), a direct comparison with our study may not be suitable because of some important differences in the experimental set up. These differences include the length of male exposure, type of mating system and climatic conditions under which the animals were raised. In addition, we have tried to partition the different male cues (olfactory, auditory, visual and tactile) rather than taking all of them together.
The exact cause(s) of spontaneous ovulation in rabbit is still a puzzle. Spontaneous ovulation leads to pseudopregnancy which is inhibitory to fertility and could cause significant economic loss in rabbit operations. Male stimuli other than coitus have been implicated in pseudopregnancy incidences by some authors. Thus it is very important to thoroughly understand the role of the buck, especially under farm production system that employs natural mating for breeding and thus house significant number of bucks together with does.Our results here indicated that:
Contact with the male improved the sexual receptivity of the doe. However prolonged visual and/or tactile contacts appeared to be detrimental to the breeding efficiency and overall productivity of the doe.
Thus it could be recommended that bucks should be kept in a section of the house which readily permit olfactory and auditory contacts with the does but partially inhibit visual contact.
Our results could be taken as preparatory to bigger projects that will employ larger number of stock.
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Received 21 June 2013; Accepted 24 July 2013; Published 1 August 2013
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