Factors associated with the pre-transport process

Transport-related activities begin with the grouping of animals; in some countries, the grouping can begin 48 hours before loading, since livestock is dispersed over large territorial extensions. The number and duration of various handling practices before loading; such as mixing of animals, food and water deprivation; represent a challenge that predisposes animals to dehydration and energy expenditure³¹.

Animals in detrimental conditions lack the same capacity to withstand long-distance transport. There are guidelines, similar to those used in Europe, to determine if an animal is fit for transport. An animal can travel if: it walks normally, carrying its weight evenly in its four legs; it is healthy, without visible disease or injury that could harm it during transport; it can stay with the group during loading and unloading; it has at least one functional eye, and it is not on late pregnancy¹⁵. Loading is more stressful for animals than the unloading process; however, the physical integrity risks of the animal are similar in both cases³². Animal loading, as well as the early stages of transport, cause high levels of stress; after this period, animals can adapt to transport conditions; however, after 12 hours, animals get tired and compromise their health, which is why transport should be interrupted^33,34. Stressors will initiate a series of reactions in the organism, with the activation of the sympathetic-adrenomedullary system and the hypothalamic-pituitary-adrenal axis, causing an increase in the levels of catecholamines and glucocorticoids³⁵, in addition to marked effects on the immune system, clearly visible in animals transported for repopulation purposes. Other repercussions can manifest several weeks after travel, such as lack of growth, low weight gain, and mortality, especially in young or recently weaned animals³⁶.

Most research on the effects of transport and its regulations has focused on transport duration; for example, in Canada, the maximum transport time is 52 hours before arriving at destination; in the USA transport should not take longer than 28 hours, and in the European Union the maximum transport time is 30 hours. However, few studies have focused on the total time in which animals are confined in vehicles, waiting before departure, transport time, type of road, number and duration of stops, waiting for unloading, among others^37,38. Factors such as the cost of transportation; truck specifications and design; loading density, vibrations, and movement; microclimate conditions; climatic and geographic conditions; route planning; factors associated with the driver and risk of accidents must be considered as a whole within transport logistics⁸.

Transport design

Livestock transport vehicles must be designed, built, and maintained in order to protect the animals from inclement weather, extreme temperatures, adverse changes in climatic conditions, and injury. Overall, there are four types of specialized vehicles: small trucks (≤3 t), individual units (>13 m long), semitrailers, and double semitrailers³. For a vehicle to guarantee greater animal comfort during transport, it is recommended to include drinking and ventilation systems, species-customized ramps, roof, non-slip flooring, lateral walls that prevent any part of the animal from leaving the truck, removable partitions to separate smaller and easier to handle groups, lateral inspection doors, and temperature control³⁹. However, the design of the truck and its impact on welfare has been poorly studied⁴⁰. In Central and South America, trucks can be articulated or not, generally without a roof, with metal or wooden structures¹³. In Latin American countries, there are laws that try to protect animals by avoiding animal cruelty and unnecessary suffering. There is also legislation on the transport of animals for consumption in most countries. However, it deals mainly with sanitary and public health requirements (vehicle cleaning, antemortem animal health inspection, and postmortem meat inspection), instead of animal welfare, such as the case of Paraguay, Peru, Colombia, Ecuador, Argentina, Venezuela, and Uruguay¹³. In Brazil, there is no specific legislation regulating the transport of farm animals, although most of the government agencies and large slaughterhouse companies are aware of the OIE recommendations. In Mexico, the Official Mexican Standard “NOM-051-ZOO-1995 for Humane practices in animal transport” covers different animal species, but is not up-to-date and has weak and not very specific stipulations in terms of transport design. In North America, including Mexico, livestock is generally transported in pot-belly trailer trucks⁴¹; these vehicles have an aluminum cover and five compartments: compartment 1 (nose), compartment 2 (belly), compartment 3 (back), compartment 4 (deck), and compartment 5 (doghouse)⁴². In Europe, single or semitrailer trucks are the most common⁴³. The choice of vehicle will generally depend on the type and quantity of livestock, the specific demands of the market, the duration of transport, and the geographical region³.

Loading density

From an economic point of view, loading density can increase or decrease operating costs per unit⁴⁴. The space required per animal during transport can be represented in three ways: (m²/100 kg), (kg/m²), and by the amount of surface used by each one (m²/animal). Other studies⁴⁵ concluded that the Space Allowance (SA=m²/animal), and an allometric coefficient that includes live weight of the animal (k=ED/PV^0.6667), was a better indicator of available space for comparisons between studies in homogeneous weight batches. The area per animal is proportional to its surface area; a 400 kg cow should be transported in an area of 1.16 m²⁽⁴⁵.

Drivers or unit operators must be careful about the space availability in their trucks and know the characteristics of the species to be transported (horned or hornless; waste, fattening, dairy, recently weaned animals, among others); this, together with climate limitations, allows defining or altering the recommended loading density⁴⁶. When the loading density is of fewer animals per square meter, animals have more room to lie down, but if the way of driving or the road conditions are poor, it will be easier for the animals to lose their balance⁴⁷. A study reported that with a density of 170 kg/m² (below the 360 kg/m² recommended by the Farm Animal Welfare Council of the USDA), animals tend to lie down during transport⁴⁸. Eldridge and Winfield⁴⁹examined the effects of different densities on long-distance transport, and although there were no effects in the ultimate pH (pHu) in beef, the incidence of bruises was higher with the lower and higher densities.

Vibration, movement, and livestock exhaustion

During transport, animals are exposed to vertical, lateral, and horizontal vibrations. Unpaved roads or roads with strong wind currents transmit a more significant amount of vibrations, animal’s sensitivity increases after long standing periods⁵⁰, causing fatigue and displacement of their gravity center, which leads to falls and injuries⁵¹. Additionally, animals make a more considerable effort seeking for a place to lean on the truck during braking⁵². Long-distance transport is so physiologically demanding that it tends to affect the neutrophil/lymphocyte (N/L) ratio, which increases the probability of opportunistic infections⁵³. Gebresenbet et al⁵⁰placed vibration sensors in a truck with an air suspension system and observed that the highest vibration level on animals was 2.27 ± 0.33 m/s² when driving in gravel roads at 70 km/h. Horizontal and lateral vibrations were lower on animals located perpendicular to the road direction. Avoiding rough, gravel, or dirt roads can reduce the exposure to vibrations, as well as using a truck that is serviced and operated by trained drivers.

The pre-transport stages produce additional energy expenditure in order to meet transport demands; however, the long periods of fasting to which the animals are subjected will have negative effects on the muscle glycogen concentration, leading to a high pHu, which will result in Dark, Firm, and Dry (DFD) meat^34,54,55. Recent reports describe the Fatigue Cattle Syndrome (FCS), animals that develop mobility problems shortly after reaching a slaughterhouse, similar to that reported in pigs. Cattle present clinical signs of tachypnea and respiratory distress, animals may also present lameness, stiff gait, or supine position in the absence of evidence indicating injury or illness, in addition to elevated concentrations of lactate and creatine kinase (CK)⁵⁶.

Temperature, microclimate, and ventilation

Theoretical estimates indicate that in a typical trailer with a recommended density for 500 kg cattle, the heat produced inside would be 13,400 watts, which is why a ventilation system is required⁴. There are two ventilation systems: passive ventilation (openings) and active ventilation (fans). Passive ventilation is given by openings throughout the truck and depends on the movement and speed of the truck⁵⁷. Active ventilation is controlled by sensors and uses extractor fans in air inlets and outlets⁷.

The microclimate inside the truck (temperature, relative humidity, and temperature and humidity index) is affected by the macroclimate, loading density, and airflow, as well as by animal respiration, transpiration, and secretions. Microclimate has a broad and potential impact on animal welfare, especially in adverse environmental conditions. Long-distance transport increases the probability of exposing animals to different climatic regions⁵⁸. For example, during the transport between Canada and the USA, temperature ranges from -42 to 45 °C³⁷. In extreme climatic conditions, the temperature inside the truck varies greatly, so the driver must be careful to open or close the ventilation openings. In warm climates, ventilation is hampered by air density, and the use of temperature and humidity recording devices is recommended so that the driver can make decisions during transport³⁶. The driver must also avoid stopping the truck for long periods since the internal temperature increases rapidly due to the external temperature, lack of ventilation, and the temperature emitted by the cattle. Under these temperature conditions, in trips longer than a day, cattle suffer an important weight loss⁵⁹. In cold climates, the incidence of post-transport morbidity and in-transit injuries caused by the freezing of sensitive body parts may increase⁴⁶. In these climates, straw bedding is recommended to improve animal comfort and to maintain a warmer temperature. High humidity conditions should be avoided during cold or hot climates since it has detrimental effects on the thermoregulatory capacity of animals^60,61. Depending on the increase in body temperature, the upper critical point for sheep and cattle is around 24-26 °C. Most mammals die when body temperature reaches 42-45 °C, which is above the normal body temperature by about 3 to 6 °C⁶². The accumulation of ammonia represents a risk in high densities and poor ventilation conditions since it correlates with temperature and air humidity⁶².

Risk factors associated with the driver

The driver’s ability to control the truck affects the quality of driving. Acceleration, braking, cornering, and driving techniques affect the ability of animals to maintain a stable posture, increasing excitability, reactivity, and injury⁶³. Moreover, the leading causes of road accidents during livestock transport in Spain, the USA, and Mexico are related to fatigue and poor decision-making by the driver, which results from long working hours, poor route design, and changes in sleep cycles²⁵. An analysis of articulated truck failures and accidents identified that the most common form of driver-associated accidents is related to an error in decision-making while driving⁶⁴. For example, the number of accidents during livestock transport in Mexico is unknown; drivers in this country frequently travel at high speeds, which affects the ability of the driver to deal with truck control in curves and other obstacles that may arise on the road¹¹.

Other factors included the age of the driver, due to the combination of experience and good health, the ideal age to drive trucks is between 28 and 54 yr old, drivers under the age of 27 obtained higher accident/fatality ranges, which increases again in drivers older than 63 yr⁶⁵. Alcohol consumption, fatigue, and chronic health problems such as being overweight or obese, are other factors associated with the driver^66,67. In a study performed in Spain, most accidents involved pig (57 %), cattle (30 %), poultry (8 %), and sheep (5 %) transport²⁵; while in another study performed in the USA and Canada, Woods and Grandin⁶⁸ found that cattle (56 %) and pigs (27 %) were the most affected species. Of these accidents, 59 % occurred between 2400 and 0900 h, most of them were overturns, similar to what was observed in a study carried out in Mexico, where overturns were the most common type of accident (58.8 %) in long-distance transport of cattle⁶⁷; these were retrospective studies based on the analysis of newspaper reports, news, and driver surveys^67,68. In this type of accident, the surviving animals are usually stunned and disoriented; they can also suffer pain, states of fear and anxiety, which complicates their handling and increases the risk of secondary accidents³.

Therefore, driver training should be a priority in the logistics chain, covering aspects of animal behavior and welfare, as well as factors related to the mechanical operation of their trucks⁴⁶. The livestock industry must take action to reduce fatigue and, therefore, the risk of accidents, which results in the loss of human and animal lives, besides significant economic losses in the logistics chain of animal transport. The only effective strategy to prevent fatigue accumulation is an ergonomic interaction of the vehicle design, besides ensuring that drivers consistently get good quality and adequate sleep⁶⁶.

Routes and geography

Geographic conditions have a strong influence on livestock production systems and on the opportunities to commercialize it. In some cases, the geographic location of a country allows or hinders international exchanges and requires a variety of different types of transport⁶⁹. In countries like Chile, it is not possible to reduce livestock transport duration due to its unique geography and few adequate routes, with transport durations of up to 63 h³⁶. Brazil is another example, with long transport periods due to its territorial extension⁶ and the global trend of reduction and specialization of slaughterhouses¹². Brazil’s road network system is over 1.6 million km long, and transport conditions vary depending on geographic characteristics. Roads are usually unpaved and in poor condition, a situation that worsens especially in the rainy season, increasing transport duration, the number of broken trucks, broken bridges, and road accidents¹³.

Live weight loss, mobility, and mortality

Live weight loss in cattle is probably the most significant economic effect of transport. In a study with a group of heifers transported 518 km (8 h), with a maximum ambient temperature of 32.2 °C, live weight decreased by 6 % after transport⁴⁸. Weight loss is the most notorious effect at first, but a primary factor is the recovery time elapsed before starting to generate weight gain in animals transferred to fattening centers. Loerch and Fluharty⁷⁰ reported that a feed and water deprivation period above 72 h in addition to an eight-hour transport reduces the total ruminal protozoa. Moreover, animals subjected to long-distance transport can suffer dehydration, especially in warm-dry or very cold climates, when the airflow inside the truck is high. Providing small amounts of nutrients or electrolytes with correct tonicity immediately before and after transport, reduces tissue dehydration and the catabolism of muscle proteins, glycogen, and lipids, as well as reducing acid-base and electrolyte imbalances⁷¹.

Another concern is the risk of disease or death due to the variable climatic conditions and toxin exposure, among other factors⁵. During transport, animals can get sick or die; these effects can occur several weeks after arriving at the destination. One of the most important diseases in cattle from intensive systems is the bovine respiratory disease. This disease usually affects young cattle, although it also increases due to the transport process to fattening units. In the USA, the bovine respiratory disease affects 14.4 % of the cattle that enter the fattening units⁷². The immune response of transported cattle is usually suppressed by the high concentrations of cortisol associated with stress⁷³, so the disease usually manifests days or weeks after arrival.

The injuries suffered during transport must be specially cared for; it is crucial to attend open wounds and keep in observation the animals that present difficulties in moving. Injured animals should receive anti-inflammatory and pain-relieving treatments to facilitate their recovery. The Fatigue Cattle Syndrome should be considered in the case of animals with mobility problems immediately after transport⁵⁶; this syndrome is accentuated in Bos indicus cattle, which is more temperamental and tends to lie down and "surrender" in trucks with high populations¹, presenting greater difficulty in adapting to confinement conditions. However, there is little information about this syndrome, and studies do not show consistent information, further information is needed. Transport mortality is a reflection of a severe welfare problem; this includes animals dead on arrival (DOA) and animals without apparent injuries (Non-ambulatory, non injured - NANI) that die at a later time⁷⁴. Mortality records during transport in commercial and experimental conditions have shown that mortality increases with high or very low temperatures, long-distance transport, or in the transport of very young animals^75,76. Transport mortality is variable and depends on different factors. Animals that lose 10 % of their body weight during transport are more likely to die or become non-ambulatory animals. Mortality also increases with lower space availability in the transport vehicle^37,38.

Bruising

Injuries and damage to the carcass caused by improper transport practices, or long-distance transport will affect the severity of bruising and, therefore, the quality of the carcass and meat. Based on the current market requirements, animal transport must avoid this type of damage. A carcass with less damage suggests better welfare conditions and, therefore, a higher ethical quality of the product. In the canal, bruising can be associated with different factors. During an experiment, the amount of bruising was higher in females than in males; also, the most severe injuries were found in old cows and not in heifers, which could be because most of these cows have a lower body condition (less muscle and subcutaneous fat). In this study, transport-related bruises were observed in a “dark red” color and therefore considered to be less than or equal to 24 h in age, bruises were found on the sides, around the hip bones (ischial tuberosity), probably due to the contact that the cattle have with the sidewalls of the vehicle; bruising increased with higher animal densities³¹.

In males, the mating behavior and headbutts, which are common behaviors in beef cattle, are related to an increase in bruising, especially in holding pens⁷⁷; in this study, the appearance of this behavior could not be related to bruising.

Strategies to reduce stress on long-distance transport

The production and transport of live cattle will continue to be stimulated by the growing human population⁷⁸, but with the integration of activities within the logistics chain, it would be possible to obtain the following advantages: 1) distance and time reduction through route optimization; 2) improve animal welfare; 3) expand the market area for producers; 4) decrease operating costs and increase competitiveness; 5) reduce carbon dioxide (CO₂) emissions; 6) improve traceability for authorities and consumers; 7) narrow the participation between producers, distributors, merchants, and consumers; 8) promote the exchange of knowledge, experience, and information⁷⁹. Important members of the industry have begun to introduce their own policies to reduce stress and improve the welfare conditions of animals for slaughter.