Sex separation unveils the functional plasticity of the vomeronasal organ in rabbits.

Chemosensory cues are vital for social and sexual behaviours and are primarily detected and processed by the vomeronasal system (VNS), whose plastic capacity has been investigated in mice. However, studying chemosensory plasticity outside of laboratory conditions may give a more realistic picture of how the VNS adapts to a changing environment. Rabbits are a well-described model of chemocommunication since the discovery of the rabbit mammary pheromone and their vomeronasal organ (VNO) transcriptome was recently characterised, a first step to further study plasticity-mediated transcriptional changes. In this study, we assessed the plastic capacity of the rabbit male and female VNO under sex-separation vs. sex-combined scenarios, including adults and juveniles, to determine whether the rabbit VNO is plastic and, if so, whether such plasticity is already established at early stages of life. First, we characterised the number of differentially expressed genes (DEGs) between the VNO of rabbit male and female under sex-separation and compared it to sex-combined individuals, both in adults and juveniles, finding that differences between male and female were larger in a sex-separated scenario. Secondly, we analysed the number of DEGs between sex-separated and sex-combined scenarios, both in males and females. In adults, both sexes showed a high number of DEGs while in juveniles only females showed differences. Additionally, the vomeronasal receptor genes were strikingly downregulated in sex-separated adult females, whereas in juveniles upregulation was shown for the same condition, suggesting a role of VRs in puberty onset. Finally, we described the environment-modulated plastic capacity of genes involved in reproduction, immunity and VNO functional activity, including G-protein coupled receptors. Our results show that sex-separation induces sex- and stage-specific gene expression differences in the VNO of male and female rabbit, both in adults and juveniles. These results bring out for the first time the plastic capacity of the rabbit VNO, supporting its functional adaptation to specifically respond to a continuous changing environment. Finally, species-specific differences and individual variability should always be considered in VNO studies and overall chemocommunication research.

Assessment of Biostimulation Methods Based on Chemical Communication in Female Doe Reproduction.

Biostimulation is an animal management practice that helps improve reproductive parameters by modulating animal sensory systems. Chemical signals, mostly known as pheromones, have a great potential in this regard. This study was conducted to determine the influence of short-term female rabbit exposure to different conditions, mainly pheromone-mediated, on reproductive parameters of inseminated does. Groups of 60 females/each were exposed to (1) female urine, (2) male urine, (3) seminal plasma and (4) female-female (F-F) separated, just before artificial insemination, and compared to a 'golden method' female-female interaction. The following reproductive parameters were analyzed for each group: receptivity (vulvar color), fertility (kindling rate), prolificacy and number of born alive and dead kits/litter. Our results showed that the biostimulation methods employed in this experiment did not significantly improve any of the analyzed parameters. However, female doe exposure to urine, especially to male urine, showed no significant higher fertility values (95.4%) when compared to the rest of the experimental conditions (on average 92.4%). Female-female interaction before artificial insemination, which is a common practice in rabbit farms, showed similar results as not establishing social interaction (F-F separated), which suggests that F-F interaction could be replaced by F-F separated, therefore avoiding unnecessary animal management and time cost. On the other hand, fertility ranges were lower for animals with a pale vulvar color whereas no differences were noticed among the other three colors which measure receptivity (pink, red, purple), thus suggesting that these three colors could be grouped together. Future studies should aim at determining potential chemical cues/pheromones released through bodily secretions that influence reproduction in rabbits, therefore contributing to animal welfare and to a natural image of animal production.

Molecular detection of myxoma virus in the environment of vaccinated rabbitries.

Myxoma virus (MYXV) is the aetiological agent of myxomatosis, a systemic, mostly lethal disease that affects European rabbits. Vaccination against it, although widespread, has not been completely effective and disease outbreaks still take place on farms which carry out vaccination programmes. Since some of these cases have been attributed to airborne transmission or the spread of the virus via inanimate vectors, the aims of this study were to determine MYXV contamination levels and distribution in the environment of vaccinated farms and to ascertain whether the detected virus corresponded to field strains. For that, environmental samples from several areas, tools and employees from four (three infected and one uninfected) rabbitries were taken and analysed by qPCR. MYXV was detected in the environment of all the infected farms, whereas all the samples from the non-infected farm were negative. Furthermore, all the positive samples contained viral DNA compatible with field strains of the virus. These results lead us to believe that the administration of currently available commercial vaccines does not prevent infected animals from shedding the field virus. Moreover, viral DNA was also found in items that are not in direct contact with the animals, which could play a role in the transmission of the infection throughout the farm and to other farms. Therefore, this study proves that current vaccination schemes on their own are not sufficient to prevent this disease and should be accompanied by adequate biosecurity measures.

Ovulation induction in rabbit does submitted to artificial insemination by adding buserelin to the seminal dose.

This study was aimed at determining if a GnRH analogue, buserelin, could be used for ovulation induction in rabbit does submitted to artificial insemination (AI) by intravaginal administration, by adding the hormone to the seminal dose. In a first experiment, 39 secondiparous experimental does (Hyplus strain PS19, Grimaud Frères, France, of about 30 weeks of age) were divided into 3 groups of 13 does each, which at the moment of AI received the following treatments, respectively: (1) control: an intramuscular injection of buserelin (0.8 microg/doe), (2) 8 microg/doe of buserelin added to the insemination dose, and (3) 16 microg/doe of buserelin added to the insemination dose. The experiment was done using 3 consecutive cycles at 42 day-intervals (n = 39). Four does from each of the 3 groups had blood taken at the fourth cycle for LH determination at 0, 60, 90, 120 and 150 min relative to AI. Kindling rates were 82% (28/34), 56% (29/36) and 85% (33/39), respectively for treatments 1, 2 and 3. In the does of groups 2 and 3, LH peaks were detected 60 min after AI, whereas in the does from group 1, the LH peak was detected 90 min after AI. Prolificacy was not different for the 3 treatments (average litter sizes ranged from 10.4 to 10.8). In a second experiment, 3 buserelin concentrations (8, 12 and 16 microg/doe) were used intravaginally and compared with the control treatment (0.8 microg/doe, via intramuscular). This experiment was done using 100 nulliparous rabbit does (Hyplus strain PS19, Grimaud Frères, France, of about 19 weeks of age) (4 groups of 25 does each) located on a commercial farm, to test if the previous results would be confirmed under field conditions. Kindling rates were no different (P < 0.05) for the 4 treatment groups [91.7% (22/24), 79.2% (19/24), 87.0% (20/23) and 87.5% (21/24) respectively for the control, 8, 12 and 16 microg of intravaginal buserelin], however, prolificacy was higher when using the maximal dose of intravaginal buserelin (11.7 vs. 9.4 for the control group). It was concluded that buserelin can be used for ovulation induction in rabbit does when included in the seminal dose, with similar AI results as those obtained when the hormone is administered intramuscularly.