Approximately 74 million rabbits were transported from farms to slaughterhouses in the European Union (EU) in 2024 (European Rabbit Association (ERA), personal communication). The transport of rabbits within the same Member State for slaughter accounts for the majority of journeys, and 99% of transport is carried out by road (1). Rabbits are usually fasted for 4–6 h prior to be transported (ERA, personal communication) and the journey time is usually under 4 h in all EU countries, with some exceptions (e.g., rerouting to another slaughterhouse due to flooding), where it can be up to 8 h (ERA, personal communication).

The legal framework for the protection of animals during transport is provided by the Council Regulation (EC) No 1/2005 of 22 December 2004 (2). However, there is a lack of specific requirements for rabbits in the current EU legislation. As a result, the stocking densities used in practice depend largely on the know-how of each integrator (3, 16).

In 2020, the “Farm to Fork” Strategy was launched with the aim of reviewing and updating EU legislation on animal welfare. Consequently, the European Commission requested the European Food Safety Authority (EFSA) to conduct a scientific review of current animal transport practices from an animal welfare perspective. As a result, in September 2022, EFSA published five scientific opinions, one of which focused on poultry and rabbits (1).

As a guideline, EFSA (1) suggested that the space allowance for fattening rabbits with a commercial body weight of 2.0–2.5 kg corresponds to the area occupied by a rabbit lying in a resting posture calculated using the allometric formula proposed by Petherick and Phillips (4). Therefore, this results in 200–215 cm²/kg (equivalent to a stocking density of 47–50 kg/m²). This is slightly higher than the area a rabbit occupies in lying position, which has been quantified at 176–194 cm²/kg or 52–57 kg/m² later by Giersberg et al. (5) through planimetric measurements. Additionally, EFSA (1) reported that the height of the containers should allow rabbits to sit in a natural upright posture without their ears touching the ceiling of the container which was suggested to be 35 cm for rabbits up to 3 kg. Otherwise, they may experience movement restriction and be unable to stretch their ears, which would impair their ability to dissipate heat under thermally challenging conditions. However, the EFSA report (1) also acknowledges significant knowledge gaps. In particular, it remains unclear whether rabbits would actually adopt this upright sitting posture on their hind legs during transport, even if sufficient height were available. More broadly, there is a lack of scientific data on how thermal conditions during transport affect rabbit posture and behaviour. Although rabbits are known to be highly sensitive to heat stress, no studies to date have systematically assessed how different temperature and humidity levels influence their behavioural responses, such as postural adjustments for thermoregulation, in the confined conditions of commercial transport crates. This lack of empirical evidence limits the ability to validate or refine current recommendations on space and container design for transported rabbits.

Following the EFSA report (1), in December 2023, the European Commission presented a proposal to revise Council Regulation (EC) No. 1/2005, with the aim of improving animal welfare during transport and aligning the legislation with best practices in animal welfare management. However, rabbits remain one of the least-studied species in this context, and scientific evidence on the necessary space and appropriate container height and the posture and behaviour in the transport crates in relation to ambient temperature and humidity during transport, remains limited.

Therefore, the objective of this study was to simulate in a climate chamber, the effect of different thermal conditions (combinations of temperature and humidity) during road transport (4 and 8 h to represent the most common and the maximum transport durations in the EU) in rabbits previously submitted to feed and water deprivation for 6 h (commercial fasting) on the posture and behaviour of fattening rabbits. These findings will support the evaluation of the minimum space allowance and height that enables rabbits to perform effective its full range of thermoregulatory behaviours in a transport container.

The animal care conditions and handling practices of the study were approved by the Ethics Committee for Animal and Human Experimentation (CEEAH) of the Universitat Autònoma de Barcelona (UAB) under protocol CEEAH 5682-CEEA-UAB on April 23, 2024.

The rabbits had a similar initial body weight after fasting across treatments (2.272 kg ± 0.124; p = 0.278). The measurements obtained from the temperature and relative humidity sensors in each of the cages placed in the climate chamber are summarised in Table 2. As shown, there were no statistically significant differences between cages, indicating that all rabbits were exposed to similar temperature and relative humidity conditions during the experimental treatment (p > 0.05).

Posture and behaviour results indicate that the combination of temperature and relative humidity were sufficient to simulate three different thermal conditions.

The objective of this study was to evaluate the posture and behaviour of rabbits of commercial body weight according to ambient temperature and humidity. This aimed to determine the minimum space allowance and height needed to allow rabbits to perform their behavioural needs, especially for thermoregulation purposes.

Regarding posture, under T3 conditions, the most frequent positions and behaviour were lateral and sternal sprawled. These can be interpreted as a heat adaptation mechanism to maximize surface contact with the floor and dissipate heat via conduction. Similar findings have been reported in other studies, indicating that a sprawled position in lateral or sternal recumbency is a reliable indicator of heat stress (9). This posture facilitates heat dissipation through the cage grid by conduction while reducing physical activity by resting, thus preventing increases in body temperature (10). Consequently, the recommended stocking density for rabbit transport should range between 36 and 60 kg/m² depending on thermal conditions, allowing rabbits to adopt their preferred resting postures under each thermal scenario (36 kg/m² to rest in a lateral sprawled position and 60 kg/m² to rest in a lying position).

It is worth noting that the area occupied by rabbits when lying down, as determined in this study, differs from estimates obtained using allometric equations developed by Baxter (11), cited by Petherick and Phillips (4) and referenced in EFSA (1). For instance, in our study, rabbits of 2.27 kg body weight occupied an average space of 382 cm² while lying down, compared to the 468 cm² estimated by the equation, which represents a deviation of 18%. Petherick and Phillips (4) acknowledge that their formula was originally designed for birds, pigs, and cattle, assuming extrapolation to other mammals, but no prior studies have empirically validated its applicability to rabbits.

On the other hand, Giersberg et al. (5) measured the space occupied by Grimoud Freres rabbits using the “KobaPlan” software (12), cited in Giersberg et al. (5). This software calculates the ground area from top-down images, using scale references and adjusting for posture and perspective. The area was computed by digital pixel counting and a linear prediction equation based on rabbit live weight was developed. In their study, the average surface for rabbits in the lying position (“sitting” as per their terminology) was 416 cm², 9% higher than our 382 cm². For sprawled sternal posture, they estimated 535 cm², 15% more than our 466 cm². However, for sprawled lateral posture, their equation estimated 565 cm², while our measurements averaged 630 cm², an 11.5% increase compared to their estimate.

Regarding rabbit behaviour, thermal treatment significantly affected the duration spent on self-grooming, exploration, inactivity, and tendencies to seek physical contact with conspecifics. As ambient temperature increased, time spent self-grooming and exploring decreased while inactivity increased, a pattern consistent with previous research (9). This aligns with findings that rabbits reduce physical activity under heat stress to avoid rises in body temperature (9). Since self-grooming and exploration require greater metabolic activity, these behaviours tend to be suppressed at higher temperatures to conserve energy and facilitate thermal regulation. Furthermore, reductions in these behaviours may reflect a negative impact on overall welfare, as they are associated with fulfilling animals’ natural needs (13).

Additionally, under T3 conditions, rabbits tended to avoid contact with their cage mates compared to T1 and T2, likely as an attempt to dissipate heat and avoid thermal load from close contact. This behaviour reflects a physiological response, as proximity increases body heat exchange between individuals. Previous studies have observed that many species, including rabbits, modify social interactions during thermal stress by seeking greater distances to reduce additional heat exposure from conspecifics (14).

In the context of rabbit transport in the EU, the most common stocking densities range between 60 and 90 kg/m², commonly around 70 kg/m² (European Rabbit Association, personal communication). Therefore, the maximum recommended density of 60 kg/m² under T1 conditions proposed here is slightly lower than that typically used commercially. It is important to highlight that as heat stress increased, rabbits tended to distance themselves from their conspecifics most of the time, suggesting that the minimum available space of 177–205 cm²/kg (i.e., stocking density of 56.5–48.8 kg/m²) may be insufficient. Greater space would not only allow rabbits to lie in preferred sprawled lateral or sternal positions but also ensure greater separation, which could help reduce heat stress and improve welfare.

Regarding height, rabbits in sternal or lateral sprawled positions, even under heat stress conditions (T2 or T3), did not raise their ears to dissipate heat, occupying a height equal to or less than 13 cm. However, in all thermal conditions tested, rabbits occasionally stood upright, reaching heights up to 32 cm. Therefore, a minimum cage height of 35 cm would allow rabbits to change posture and stand without their heads touching the cage grid.

It is important to emphasize that this study was conducted under experimental conditions using cages of 35 cm height as transport containers with an available space of 714 cm²/kg (i.e., stocking density of 14 kg/m²), housing two rabbits per cage. Thus, the effects of varying thermal conditions (temperature, relative humidity, wind speed), available space, and container height in commercial transport on behaviour, thermophysiological, and metabolic responses remain unknown. Consequently, this study serves only as a preliminary approach to defining space and container height treatments for evaluation in future studies.

As a next step, a follow-up study has already been carried out under controlled experimental conditions to specifically assess the combined effects of different space allowances and container heights under a range of thermal scenarios. The final validation of science-based recommendations for rabbit transport will rely on the integration of results from the present study, the follow-up experimental trial, and a third study currently underway under real commercial transport conditions. Together, these studies aim to provide robust empirical evidence to inform future regulatory decisions and support the development of species-specific requirements for rabbits in the revision of Council Regulation (EC) No 1/2005, in line with the objectives of the Farm to Fork Strategy.

A minimum available space of 168 cm²/kg, or the equivalent of a maximum stocking density of 60 kg/m² under thermal comfort conditions, is established to allow all animals to lie down simultaneously. For all rabbits to sprawl laterally or sternally to dissipate heat, under static conditions without ventilation, an available space of 205 cm²/kg is required for sternal sprawl (equivalent to a maximum stocking density of 36 kg/m²), and 277 cm²/kg (equivalent to a maximum stocking density of 49 kg/m²). Increasing the available space beyond these minimums may further facilitate heat loss and help prevent full-body contact between animals, thus improving thermal comfort. The minimum cage height that allows rabbits of commercial weight (2.0–2.5 kg live weight) to change posture and stand upright without their heads touching the cage grid is set at 35 cm.

Rabbit posture and behaviour did not differ significantly between the 4-h and 8-h time points. The most common behaviour observed was inactivity, followed by self-grooming, regardless thermal conditions. However, as thermal conditions became more challenging, self-grooming decreased while inactivity increased further. Rabbits remained in an upright position approximately 1% of the time, irrespective of the thermal conditions.

Given the methodological limitations, these recommendations should be explicitly framed as preliminary indications that require validation under commercial transport conditions.