Rigorous review of the available scientific basis on canine and feline chronobiology, physiological impact of transport, and plausibility of a post-flight circadian desynchronization syndrome in these species, distinguishing direct evidence from well-founded biological inferences.
Jet lag in human medicine is a well-defined chronobiological syndrome, produced by rapid displacement across multiple time zones and characterised by misalignment between the individual's internal clock and local environmental time. Its manifestations include insomnia or hypersomnia, fatigue, cognitive impairment, gastrointestinal alterations and irritability. The central pathophysiology involves the suprachiasmatic nucleus (SCN) of the hypothalamus, which acts as the central pacemaker of the circadian system and resynchronises more slowly than environmental stimuli after an abrupt time-zone change.
The use of the term «jet lag» in the veterinary context is functionally descriptive but scientifically imprecise. For the human syndrome to be directly extrapolable to a dog or cat, at least two conditions would need to be met: that the animal has an equivalent functional SCN with similar resynchronisation properties, and that the animal subjectively experiences temporal misalignment. The first condition is reasonably supported by anatomical and physiological evidence; the second cannot be verified with current tools.
This article therefore adopts a conservative and verifiable position: to speak of circadian desynchronization and transport stress as documented or plausible mechanisms, using «jet lag» exclusively as an operational term for outreach.
It is conceptually important to distinguish the two mechanisms that converge in the animal that has just completed a long-haul transmeridian flight:
| Circadian desynchronization | Acute transport stress | |
|---|---|---|
| Mechanism | Mismatch between the internal clock and the zeitgebers of the new environment (light, feeding schedules, activity routine). | Activation of the SAM and HPA axes by the physical and environmental stressors of travel: confinement, noise, motion, temperature, pressurisation, water and food deprivation. |
| Temporal scale | Days to weeks (gradual resynchronisation process). | Hours to 2-3 days (recovery from acute stress response, according to Leadbeater et al., 2021). |
| Evidence in dogs/cats | Indirect (social jetlag in dogs, Wenchner 2024). Biological inference for transmeridian flights. | Direct and documented (Leadbeater 2021; Wormald 2017; Beerda 1998). |
| Manifestations | Sleep alterations, behavioural changes, temporal disorientation. | Elevated cortisol, tachycardia, panting, inappetence, GI changes, lethargy. |
In pet relocation practice, both mechanisms coexist and reinforce each other. An animal that arrives stressed in the new environment has compromised capacity to resynchronise quickly because stress itself alters circadian rhythms. This overlap is why the post-flight adaptation period cannot be simplified to a single linear process.
The mammalian circadian system is organised hierarchically. The SCN of the anterior hypothalamus acts as the master pacemaker: it integrates light information received via the retinohypothalamic tract and coordinates peripheral clocks present in virtually all tissues of the organism (liver, intestine, muscle, skin). This architecture is evolutionarily conserved in all mammals, including dogs and cats, making it biologically plausible —though not specifically proven for transoceanic flights— that perturbations in SCN input stimuli produce desynchronization in these species.
Peripheral clocks can desynchronise from each other and from the SCN when the zeitgebers that govern them do not change simultaneously. This is precisely what happens in a transmeridian flight: light in the new environment can change abruptly, but feeding schedules, ambient temperature and owner activity patterns adapt at different rhythms. The result is internal discoordination that, in humans, produces measurable symptoms.
The term zeitgeber (from German: «time giver») designates the environmental stimuli that synchronise the internal clock with the 24-hour environmental cycle. In mammals, the main zeitgebers are:
The relevance of listing zeitgebers in the context of air transport is that all of them are perturbed simultaneously during a long-haul flight: light exposure changes (dimmed cabin or artificial light), the animal may not receive food for 8-12+ hours, cargo hold temperature varies, and social interaction with the owner is nil or minimal. The flight is, in this sense, a simultaneous multizeitgeber perturbation.
Dogs: Zanghi (2016) demonstrated through 24-hour activity monitoring that the domestic dog has a diurnal-crepuscular rhythm pattern but one highly mouldable by the owner's schedule. This adaptability, which favours cohabitation, also implies that the dog is especially vulnerable to desynchronization when the owner's schedules change abruptly —exactly what happens in a time-zone change.
Social jetlag in dogs (Wenchner et al., 2024): This study published in Scientific Reports is the most relevant and recent finding for this article. The authors documented that dogs whose owners change their schedules between weekdays and weekends (the so-called human «social jetlag») show measurable alterations in sleep quality and activity patterns. This is the first study to demonstrate directly that dogs suffer circadian desynchronization in response to changes in human cohabitation schedules — a mechanism directly analogous, though not identical, to that triggered by a transmeridian flight.
Cats: Piccione et al. (2013) documented the circadian body temperature rhythm in domestic cats, confirming a crepuscular pattern with activity peaks at dawn and dusk. Randall et al. (1985) demonstrated that the light/dark cycle is the dominant regulator of feline activity, with greater adaptive rigidity than in the dog. This lower plasticity makes the cat potentially more vulnerable to abrupt light perturbations such as those produced by a night flight across multiple time zones.
Unlike circadian desynchronization per se, the physiological impact of air transport stress in dogs is documented with direct evidence of acceptable quality.
Leadbeater et al. (2021, Veterinary Record): This is the most comprehensive study available on canine welfare during transport. The authors documented salivary cortisol peaks during and after air transport, with values that in some individuals took up to 48 hours to return to baseline. This finding has direct practical implications for the post-arrival observation period.
Wormald et al. (2017, Applied Animal Behaviour Science): Quantified tachycardia and panting as markers of SAM (Sympathetic-Adreno-Medullary) axis activation in dogs during transport. These parameters are indicators of acute sympathetic activation, consistent with the initial phase of the stress response: release of adrenaline and noradrenaline by the adrenal medulla.
Beerda et al. (1998, Physiology & Behavior): Established the reference parameters for urinary and plasma cortisol response in dogs under environmental stressors, including confinement and novelty. It is the methodological reference that allows interpretation of cortisol values in more recent studies.
Extrapolation note: the mechanism described in this section is mainly documented in humans and rodents. Its application to dogs and cats is stated as a biological inference based on evolutionarily conserved mechanisms.
The relationship between the stress axes and the circadian system is bidirectional and of particular relevance for understanding why the post-flight adaptation period is more complex than simply resetting a clock:
Pastore et al. (2011, Animal Welfare): This study confirmed that the dog has a circadian cortisol rhythm similar to the human, with a morning peak. This basis is essential to be able to speak of «HPA axis desynchronization» as a plausible phenomenon when the dog arrives in a time zone where the «morning peak» should occur at a time that its internal clock still registers as another time of day.
Transport stress can explain, through well-documented mechanisms, three of the most frequently reported manifestations in the post-flight period:
This section describes the behavioural and physiological alterations frequently reported by owners and veterinarians in the immediate post-flight period (first 24-72 hours) and in the intermediate adaptation period (approximately days 3-14). The language used is deliberately conservative: manifestations are described as «frequently reported» or «compatible with» the mechanisms described, not as causally established consequences.
These are the manifestations most directly related to circadian desynchronization and the most frequently reported in dogs that have completed transmeridian flights of more than 6 time zones:
Inappetence in the first 12-24 hours post-travel is a frequently reported manifestation and biologically coherent with residual sympathetic activation and prolonged fasting during the flight. In most cases, appetite normalises within 24-48 hours. Changes in the timing of food demand (the animal asks for food at times that do not correspond to its new environment) are compatible with persistence of the gastrointestinal peripheral clock circadian rhythm. Since feeding schedules are a zeitgeber, irregularity in meals in the post-travel period may prolong desynchronization.
Soft or variable-consistency faeces, isolated vomiting episodes and flatulence are frequently reported in the post-travel period. Interpretation of these signs must be made in the context of the complete journey: pre-travel fasting (many airlines and protocols recommend food restriction 4-8 hours before the flight; prolonged fasting followed by refeeding can produce transient changes in motility and microbiota); travel stress (HPA axis activation alters GI motility and may temporarily compromise intestinal epithelial barrier function); water change (water at the new destination may have different mineral composition). The presence of persistent GI signs (beyond 48-72 hours), haematemesis, melaena or systemic signs requires veterinary evaluation.
Hypervigilance and excessive exploration: compatible with residual sympathetic activation and the biological need to map a new environment. Lethargy: frequent in animals whose travel stress was more intense or prolonged; compatible with the exhaustion phase that follows sustained HPA axis activation. Nocturnal vocalisation: especially in dogs with predisposition to separation anxiety; compatible with the combination of temporal disorientation and residual activation. Inattention or apparent disorientation: compatible, according to Kis et al. (2014), with REM sleep alteration and its role in spatial and contextual memory consolidation.
| Parameter | Dogs | Cats |
|---|---|---|
| Activity pattern | Diurnal/crepuscular, highly adaptable to human schedule (Zanghi, 2016) | Fundamentally crepuscular, with greater adaptive rigidity (Randall, 1985) |
| Circadian plasticity | High: canine rhythm can be modulated by owner social jetlag (Wenchner, 2024) | Lower: light/dark cycle is the dominant regulator |
| Response to transport stress | Documented: cortisol and cardiorespiratory parameters (Leadbeater 2021, Wormald 2017) | Less studied; rupture of the bond with the known environment elevates stress response (Vitale, 2019)* |
| Tolerance to confinement | Variable; correlates with temperament and prior conditioning | Generally lower; the territory-dependent cat is more vulnerable |
| Expected resynchronisation speed | Inferred: hypothesis of 2-5 days for 6-12 time-zone changes (extrapolation from human model) | Inferred: possibly slower due to lower circadian plasticity; not quantified |
* Vitale et al. (2019, Current Biology): study on the attachment bond between cats and humans. Used here as a conceptual framework to argue that rupture of the known environment activates the stress response in cats. Not an air transport study; stated as framework reference, not direct evidence.
Puppies (< 6 months): the circadian system is not fully mature; the stress response may be more intense; prolonged fasting has more severe metabolic consequences in young small-sized animals. Geriatric animals (> 8-10 years): Bognár et al. (2021) documented that sleep fragmentation increases with age in dogs; geriatrics may have a slower resynchronisation window. Chronic disease: pathologies affecting the HPA axis, CNS, GI tract or renal function may decompensate due to transport stress. Brachycephalic breeds: upper airway compromise amplifies transport stress under elevated temperature or confinement conditions.
Methodological note: the relationship between number of time zones and magnitude of desynchronization is well documented in humans. Its application to dogs and cats is presented as a working hypothesis applied to routine desynchronization, not as a proven fact in these species.
In human medicine, jet lag severity correlates with: (a) the number of time zones crossed, (b) direction of travel (eastbound flights generate greater desynchronization than westbound), and (c) individual traveller characteristics. Applying this framework as a working hypothesis to companion animals:
| Category | Time-zone change | Expected implication for routines |
|---|---|---|
| Low | 1-3 time zones | Mild mismatch in feeding and walking schedules. Resynchronisation expected in 1-3 days with maintenance of routines. |
| Moderate | 4-7 time zones | Significant mismatch of the light/dark cycle. Sleep and appetite alterations likely for 3-7 days. Requires active zeitgeber management. |
| High | 8-12+ time zones | Maximum mismatch, including potential partial cycle inversion. The adaptation period may extend to 7-14 days. Vulnerability amplified in geriatrics and puppies. |
Re-entrainment is the process by which the circadian system resynchronises with the zeitgebers of the new environment. In humans, the rule of thumb is approximately one day of adaptation per time zone crossed. In dogs and cats, this parameter has not been specifically measured.
Light/dark cycle: exposure to natural light in the new environment at the correct times of day (morning at destination) accelerates SCN resynchronisation. Feeding schedules: maintaining regular schedules adapted to the new time zone from day one activates one of the most relevant zeitgebers for peripheral clocks. Activity and socialisation routines: maintaining regular walking, play and interaction routines at the new destination's times provides social and activity zeitgeber signals. Expected time frame (working hypothesis): in the absence of specific data for dogs and cats, it is reasonable to estimate that healthy adult animals achieve functional resynchronisation in a period of 3 to 10 days for 6-12 time-zone changes, with significant individual variability.
Dunlap et al. (2015, AJVR): documented that endogenous melatonin plasma levels in dogs are significantly lower than in humans. This quantitative difference questions the direct extrapolation of human dosing protocols to the dog. There is no controlled clinical trial that has evaluated exogenous melatonin for post-flight resynchronisation in dogs or cats. Melatonin is not prescribed or recommended in this article. It is stated as an area with insufficient evidence for the specific use of air jet lag in pets.
| Controllable variable | Chronobiological and stress relevance |
|---|---|
| Time of arrival at destination | Arriving in the morning or early afternoon at destination facilitates correct light exposure from day one. |
| Duration of layovers and waits | Prolonged airport waits amplify sustained HPA axis stress. Direct routes or short layovers reduce total duration of stress activation. |
| Prior familiarisation with the crate | An animal that perceives the crate as a safe space has a significantly lower stress response during the flight. |
| Transport environment temperature | Comfort temperatures (18-24°C) reduce the total physiological load of the journey. |
| Pre-flight hydration | Water fasting should be minimised. Dehydration amplifies the stress response. |
| Keeping the owner's scent | An item with the owner's scent in the crate acts as a social safety signal and reduces SAM axis activation. |
Lighting: practically nil or very low; the animal is in darkness for most of the flight. Noise: the level in cargo holds is high (70-85 dB or more in cruise); it is a significant and sustained stressor. Temperature: regulated in animal-eligible cargo holds according to IATA standards, but with variability during tarmac embarkation/disembarkation. Pressurisation: equivalent to approximately 1,500-2,400 m altitude; there is no evidence that relative hypoxia at this altitude has relevant clinical impact in healthy animals.
Prioritise access to clean water at destination immediately upon arrival. Do not force feeding if the animal shows inappetence in the first 4-6 hours. Expose the animal to natural light in the new environment during daytime hours at destination. Maintain destination routines (meal times, walks) from day one, not adapted to origin time. Reduce additional stressors: visits, environment changes, introductions to other animals. If GI signs, inappetence or behavioural alterations persist beyond 48-72 hours, consult a veterinarian at destination.
| Claim / Mechanism | Type of evidence | Main source |
|---|---|---|
| Air transport elevates cortisol in dogs for up to 48h | Direct evidence — study in dogs | Leadbeater et al. (2021) |
| Transport induces tachycardia and panting in dogs | Direct evidence — study in dogs | Wormald et al. (2017) |
| Dogs have circadian cortisol rhythm with morning peak | Direct evidence — study in dogs | Pastore et al. (2011) |
| The dog has measurable chronotype; sleep fragments with stress | Direct evidence — study in dogs (actigraphy) | Bognár et al. (2021) |
| Human social jetlag desynchronises dog sleep | Direct evidence — study in dogs | Wenchner et al. (2024) |
| The cat is crepuscular with circadian body temperature rhythm | Direct evidence — study in cats | Piccione et al. (2013) |
| Light/dark cycle regulates cat activity | Direct evidence — study in cats | Randall et al. (1985) |
| Cortisol desynchronises peripheral clocks | Human/rodent evidence — STATED EXTRAPOLATION | General chronobiology literature |
| A transmeridian flight produces jet lag in dogs/cats | NO direct evidence — biological inference | Theoretical model built in this article |
| Post-flight resynchronisation time in dogs/cats | NO direct evidence — working hypothesis | Extrapolation from human model |
The five most relevant evidence gaps: (1) Real jet lag in cats: there are no studies of physiological desynchronization by time-zone change in domestic cats. (2) Melatonin and air jet lag: there is no controlled clinical trial that has evaluated exogenous melatonin for post-flight resynchronisation in dogs or cats. (3) Intestinal microbiota and time-zone change: there is no equivalent evidence in dogs or cats. (4) Resynchronisation kinetics: the exact biological resynchronisation time post-transmeridian flight in dogs and cats is unknown. (5) Physiology during flight: there are no actigraphy or continuous cortisol, heart rate or temperature monitoring studies conducted during flight in the cargo hold.
Longitudinal actigraphy studies pre/during/post-flight; non-invasive biomarkers (salivary and faecal cortisol with serial sampling); heart rate variability (HRV) as an indicator of autonomic activation; comparative dog vs. cat studies under controlled time-zone change conditions; non-pharmacological zeitgeber interventions evaluated with biomarkers.