Abstracts of the 45th Symposium on Cuniculture, ASESCU

The 45th Congress of the Spanish Association of Cuniculture (ASESCU), co-organised by the Spanish Association of Cuniculture (ASESCU) and Grupo Editorial Agrícola-Henar Comunicación Agroalimentaria, was online held on 6th and 7th October, 2021. The four main talks were mainly focussed on “In-farm composting. Enhancing the value of rabbit manure” by Raúl Moral (University Miguel Hernández, Spain), “Recent advances in artificial insemination” by Pilar Viudes (Instituto Valenciano de Investigaciones Agrarias, Spain), “The necessary transition of rabbit farming in Europe. The French Example” by Davi Savietto (INRAE, France), and “Social networks in rabbit farming. A practical view” by Jesús López (Grupo Editorial Agrícola-Henar Comunicación Agroalimentaria, Spain). A commercial speech on “Building immunity for a healthier world” was also presented by Sandra Gascón (Hipra). Two round tables were also held: the first on “News in veterinary prescription” with the participation of María Hernández (Spanish Ministry of Agriculture) and Mario Malo (Spanish Association of Veterinarians specialised in Rabbit Farming), and the second on “Rabbit meat processing and new products” with the participation of Raúl Grau (Universitat Politècnica de València, Spain) and María Luz de Santos (Spanish interprofessional organization to promote the rabbit sector, INTERCUN). Moreover, a total of 14 oral communications were presented by research teams from Spain, Algeria, Venezuela, Portugal and Italy. The congress was attended by around 130 participants from several European, American and African countries. Abstracts of the contributions presented are reported below.

Levels of testosterone, progesterone and oestradiol in pregnant-lactating does in relation to aggression during group housing

The neuroendocrine regulation of rabbit maternal behaviour has been explored in detail. However, little is yet known about the hormonal regulation of aggression in concurrently pregnant-lactating does, a reproductive condition that prevails during group housing of rabbits on farms. Therefore, in this study we determined the relation between a) the levels of progesterone, testosterone, and oestradiol during lactation; b) the anogenital distance at artificial insemination; and c) the timing of grouping with the intensity of agonistic behaviour, published previously. We performed four consecutive trials, where three groups of eight does each were artificially inseminated on day 10 postpartum (pp) and grouped on either day 12, 18 or 22 pp. Using Dipetalogaster maxima, a reduviid blood-sucking bug, we collected blood samples during the pregnant-lactating phase (days 13, 15, 17, 19, 21, 23 pp) on one or two randomly chosen does per treatment group. Testosterone levels varied little across the pregnant-lactating phase, agreeing with results from pregnant-only rabbits, while progesterone levels increased from day 3 (=13 dpp) to day 7 (=17 dpp) and remained unchanged until day 13 (=23 dpp) of pregnancy. All oestradiol concentrations fell below the limit of detection. Overall, all concentrations were slightly lower in comparison to rabbit studies with pregnantonly does. The agonistic behaviour was not related to the respective hormonal concentrations at grouping. In conclusion, the time point of grouping does after artificial insemination (AI) in the semi-group housing system only had a weak influence on aggression and the hormonal profile did not indicate an optimum time for grouping.

Genetic factors of functional traits

Selection of functional traits is a challenge for researchers, but an increasingly necessary objective due to the growing concern regarding animal welfare and overcoming the problems of reducing antibiotic use in rabbit production without undermining the animals’ productivity. The aim of this review is to discuss the genetic control of resistance to diseases, longevity and variability of birth weight within a litter, or litter size variability at birth within doe, describing the selection programmes and the first results from a multi-omics analysis of resistance/susceptibility to diseases. The heritability is around 0.13 for longevity, 0.01 for uniformity in birth weight, 0.09 for litter size variability and around 0.11 for disease resistance. Genetic correlations between functional traits and production traits are mostly no different from zero, or are moderately favourable in some cases. Six selection programmes developed in three countries are reviewed. Line foundation with high pressure for selection or divergent selection experiments are different methodologies used, and favourable responses to selection have been achieved. Genomics studies have revealed associations in regions related to immune system functionality and stress in lines selected for litter size variability. Knowledge of the role of gut microbiota in the rabbit’s immune response is very limited. A multi-omics approach can help determine the microbial mechanisms in regulation immunity genes of the host.

Neuroendocrinology applied to rabbit breeding

Successful rabbit production relies heavily on the use of adequate practices that enhance specific aspects of reproduction, such as mating, ovulation and lactation. Regardless of the type of production unit or strain of rabbits used, these processes rely on a complex chain of neuroendocrine steps that include particular hormones, peripheral stimuli and activation of discrete brain regions. Such is the case, for instance, of reflex ovulation, which occurs in response to copulation but is inhibited throughout lactation. Little is known about the mechanisms mediating lactational anoestrus and the restoration of oestrus following the cancellation of a single suckling episode (biostimulation). Nevertheless, the latter procedure (adopted worldwide to accelerate reproduction) has unwanted consequences for the doe and her litter. After successive episodes of biostimulation, the former shows a loss of fertility and body mass. In the kits, alterations are observed in their neuroendocrine response to mildly aversive stimulation in adulthood, as well as reductions in sexual behaviour. In addition to milk intake, a good nest is essential for normal litter growth and development. If this is not available, or if it deteriorates, rabbit caretakers can easily (re) build one from hair sheared off other rabbits or using synthetic material. Lactating does will nurse equally well their own or ‘alien’ young, placed inside the nest. It is crucial to have a minimum of six suckling kits in the nest, as the doe relies on this stimulation to maintain a normal nursing behaviour, i.e., only once a day throughout lactation. Recent work is revealing the similarities and differences in the responsiveness to mating among oestrous, lactating and biostimulated does. The relevance of these findings for the likelihood of reflex ovulation and the additional contribution of factors contained in the semen warrant more in-depth research. New insights on these issues, essential to reproductive neuroendocrinology, can emerge by fostering a richer interaction between academic laboratories and rabbit production settings worldwide.

Physiology and modulation factors of ovulation in rabbit reproduction management

Rabbit is an induced ovulatory species, so ovulation takes place after mating. Traditionally, exogenous and synthetic hormonal factors (administered by intramuscular and intravaginal route) such as GnRH and analogues, or different physical procedures (i.e. stimulation by intravaginal cannula) have been used to induce ovulation in females when artificial insemination is applied in rabbit farms. Restriction and public rejection of the use of hormones is leading to the study of the seminal plasma components with potential action on ovulation induction. The aim of the present review is to collect and summarise the strategies used in recent years to trigger ovulation and improve rabbit fertility management with respect to more animal-friendly manipulation methods. Furthermore, special attention has been paid to the use of a semen component (as endogen molecule) such as beta nerve growth factor (β-NGF) in male and female rabbit reproductive physiology. This neurotrophin and its receptors (TrKA and p75NTR) are abundantly distributed in both male and female rabbit reproductive tracts, and it seems to have an important physiological role in sperm maturation and behaviour (velocity, apoptosis and capacitation), as well as a modulatory factor of ovulation. Endogen β-NGF is diluted in the seminal doses with the extenders; hence it could be considered an innovative and alternative strategy to avoid the current exogenous (by intramuscular route) and stressful hormonal treatments used in ovulation induction. Their addition in seminal dose could be more physiological and improve animal welfare in rabbit farms.

Relationship between rectal temperature measured with a conventional thermometer and the temperature of several body regions measured by infrared thermography in fattening rabbits. Influence of different environmental factors

In clinical examination of rabbits, the temperature is usually recorded with a digital thermometer introduced rectally, an invasive procedure that could cause handling stress. The aim of this study was to assess body temperature using infrared thermography (IRT) in four areas of the rabbit’s anatomy: eye (ETT), outer ear (OETT), inner ear (IETT) and nose (NTT), and then validate it as an alternative measure to rectal temperature (RT) assessed with a conventional thermometer. Temperature samples were taken twice a week from 48 weaned rabbits of Spanish Common Rabbit breed during a 38-d fattening period. The factors considered were: doe from which the rabbits came (8 does), weeks of fattening period (4 to 5 wk), batch (3 periods of the year: April-May, June-July and January-February) and group size (cages with 1 to 7 rabbits). On average, the results were an RT of 38.48±0.02 °C; ETT of 37.31±0.05 °C; OETT of 29.09±0.26°C; IETT of 30.53±0.251 °C, and NTT of 33.29±0.11 °C (mean±se). Moderate, statistically significant positive correlations (PP

Rabbit meat: valuable nutrition or too-cute-to-eat?

Rabbit meat is a component of traditional diets, often incorporated into iconic dishes of regional cuisine. Its consumption can be traced back to the ancient civilisations of the Mediterranean and beyond, well into the Palaeolithic era. Even though it has been representing considerable nutritional and cultural value for millennia, a decline in consumption is now noticeable. Specific categorial dynamics are at play, related to the various superimposed roles of rabbits as livestock, game, pests, laboratory animals and pets. Their perceived cuteness in particular can lead to emotional responses that are hard to reconcile with the sensitivities of the post-domestic paradigm. Such effects compromise the acceptability of rabbit meat in contemporary Western societies that are typified by problematic human-animal interactions and a disconnect from the food chain. Young and urban populations in particular now seem to have difficulties facing the notion that food production requires the killing of animals. As a result, a traditional food source risks becoming irrelevant despite its high nutritional value and potential for sustainable meat production, due to reasons that are emotive rather than rational.

Effect of housing enrichment and type of flooring on the performance and behaviour of female rabbits

This study investigated the effect of housing enrichments (scratching card, gnawing material and a platform), of a change in height and in the type of flooring on the live weight, reproductive performance and behaviour of female rabbits, as well as on the feed intake and spatial distribution of females and their kits. A total of 40 multiparous female rabbits were monitored in three consecutive reproductive cycles (48-d intervals). Four days before parturition in each reproductive cycle, the females were randomly assigned to one of the five types of housing: Control (CNT: 102×47×30 cm, L×W× H); Scratching card (SCT: containing a scratching card); Gnawing materials (GNW: CNT dimensions plus a compressed lucerne hay block and a wooden stick); Platform (PLT: 102×47×60 cm, including a platform with a plastic floor) and Combination (CBN: PLT dimensions with the scratching card, the gnawing materials and a platform). Data were only recorded during the first and third reproductive cycles. The living conditions did not significantly alter the females’ live weight (4889 g at housing; 4890 g at mid-lactation; 4867 g at weaning), reproductive performance (9.0 kits born alive), survival of the kits (90%), nor the feed intake of females and their litters (542 g/day). Providing animals with a gnawing block stimulated Gnawing behaviour (median frequency per group: CTL=0.00, SCT=0.00, GNW=4.69, PLT=0.00, and CBN=2.34; PRearing up behaviour (median frequencies per group: CTL=0.00, SCT=0.00, GNW=0.00, PLT=2.08, and CBN=3.12; P=0.06), and when a platform was present, the rabbits used it (mean values per group: CTL=0.00, SCT=0.00, GNW=0.00, PLT=1.79, and CBN=4.91; P=0.003). Regarding the type of floor, females appeared to prefer the plastic mesh flooring (31.2%) to the wire mesh flooring (18.8%). To sum up, providing female rabbits with simple enrichments appears to stimulate specific behaviours like Gnawing and Rearing up and may contribute to their wellbeing.

Hierarchical clustering as a tool to develop a classification scheme for rabbit meat quality

<p>This study aimed to characterise the quality of meat from commercially-raised rabbits. Animals came from five different producers and were laughtered in three different plants under provincial or federal inspection jurisdiction. Animal behaviour evaluated by scan sampling prior to feed withdrawal (FW) and transport, as well as blood lactate concentration at exsanguination, did not raise concerns with respect to stress. Stomach pH was higher (<em>P</em>=0.047) when the FW time was short (≤13.5 h), at a mean value of 2.23. All pH values measured 1 h post-mortem from the Biceps femoris (BF) and almost all (97.6%) from the Longissimus lumborum (LL) were higher than 6. Values for ultimate pH measured 24 h postmortem(pH_u) ranged from 5.80 to 6.83 and from 5.70 to 6.70 for BF and LL muscles, respectively. The maximum meat drip loss recorded was 2.6%, while cooking loss reached 30%. Meat lightness (L*) and colour intensity (C*) for the long FW times (≥23 h) were no different from those with short and intermediate (15.5 to 17.3 h) FW times. However, these colour parameters were higher for the short FW time class compared to the intermediate FW time class (<em>P</em>&lt;0.02). A hierarchical cluster analysis based on pH_u, cooking loss and lightness (L*) from 200 rabbit loins was performed. Of the four clusters created, clusters 1 and 2 had the best and second-best meat quality, respectively. Clusters 3 and 4 had the lowest meat quality and presented DFD-like (dark, firm and dry) characteristics. Meat did not exhibit PSE-like (pale, soft, exudative) characteristics, even for the slaughter lot with the minimum mean pH_u. Of the eight slaughter lots evaluated, more than 50% of the meat from three of them fell into clusters 3 and 4; all three were in the intermediate FW time class. Overall, the quality of rabbit meat analysed was acceptable for commercial use, but rather variable. This suggests that there are factors within the value chain that are not yet fully controlled and require further investigation.</p>

Pituitary and ovarian hormones: is their plasma concentration affected by litter size in primiparous lactating rabbit does?

Genetic selection in commercial rabbit lines based on litter size has positively improved the number of kits suckling, presumably to weaning. Although it has been proven that the energetic balance of primiparous does is due to the need to satisfy pregnancy, lactation and growth requirements, litter size adjustment from 7 to 12 kits is applied as a routine in commercial rabbit farms. The suckling stimulus provokes a prolactin (PRL) secretion, which in turn can modulate the preovulatory release of luteinising hormone (LH) and, consequently, the ovulatory and productive responses of the does. This study aimed to determine if litter size of prolific primiparous rabbit does during lactation [Group HL, with high litter density (10-12 kits; n=21) and Group LL, with low litter density (7-9 kits; n=29)] influences plasma concentration of PRL. Blood samples from lactating does were taken weekly throughout lactation starting on day 4 post-partum, until day 32 post-partum, before and immediately after suckling. In addition, the does were re-inseminated after weaning (day 32 post-partum), and sampled at 0 and 60 min after induction of ovulation to determine whether litter size affected the peak of LH, progesterone (P4) concentrations and the main productive parameters of their second pregnancy. All hormones were determined by enzyme immunoassay. Statistical analysis of the results revealed that the PRL concentrations of hyperprolific rabbit does before and immediately after a suckling stimulus from 7-9 or 10-12 kits were significanltly different, as we only detected basal levels, with a rise after weaning in both groups. More studies are necessary, delaying blood sampling to later periods of time after the suckling stimulus, in order to conclude whether the peak release of this hormone is altered or not. There were also no differences in plasma LH and progesterone levels after artificial insemination, or in productive performance of these females after their second pregnancy. In conclusion, the litter size adjustment of prolific primiparous rabbits with 7 to 12 kits determines adequate pituitary, ovarian and reproductive responses at second parturition if the does are inseminated after weaning.