4 Pre-slaughter Phase
4.1 Farm-to-Abattoir Phase
100,000 animals per year, and the average throughput of these plants is nearly 200,000 per year. There are therefore fewer local abattoirs and the remaining larger plants operate at higher line speeds. Faster processing requires moving animals more quickly and this is likely to be more stressful.
Effects on welfare and quality
A number of quality problems attributable to pre-slaughter handling can be recognized and these generally also reflect poor welfare. Animals may die, they may suffer trauma such as bruises or broken bones, long periods without food may reduce carcass yield, deprivation of water may cause dehydration, and stress may produce poor quality of the lean meat. In particular, short-term (acute) stress may stimulate glycolysis immediately post-mortem and produce PSE (pale, soft, exudative) meat, and long-term (chronic) stress may deplete muscle glycogen levels and produce DFD (dark, firm, dry) meat. The transport of animals can spread disease, which has implications for both welfare and quality, and may compromise traceability if systems for animal identification are less than perfect.
Effective traceability, so that the exact origin and provenance of each piece of meat sold at retail are known, is central to the quality control of hygiene and safety.
Legislative control of transport and animal handling procedures
In the UK the handling of animals during the period from farm to slaughter is currently controlled by four main pieces of legislation.
Transport is governed by The Welfare of Animals (Transport) Order 1997, handling in markets by The Welfare of Animals at Markets Order 1990, and handling at the abattoir by The Welfare of Animals (Slaughter or Killing) Regulations 1995 and The Fresh Meat (Hygiene and Inspection) Regulations 1995. UK legislation reflects EU Directives, so in general terms European legislation is harmonized. The general provisions of The Welfare of Animals (Transport) Order 1997 make it an offence to cause injury or unnecessary suffering or to transport unfit animals.
Transporters must be authorized by the appropriate Government Minister, animal handlers must be competent (as demonstrated by training or experience) and all journeys must have appropriate documentation. The Order prescribes amongst other things, maximum journey times, space requirements and feeding and watering intervals.
Although legislation is always subject to change the general principles embodied in it are unlikely to. In general, if there is change, it tends to be in the direction of stronger protection for the welfare of animals. For example, there is currently much pressure to reduce maximum permitted journey times.
Fitness to travel
Animals that are ill, infirm or fatigued (unless only slightly affected and where the intended journey is unlikely to cause them unnecessary suffering) are unfit to be transported. Transport is prohibited in pregnant animals (likely to give birth, or within 48 h of birth) or new-born animals in which the navel has not completely healed. Animals must be able to be loaded without using force and be able to bear weight on all four legs.
Examples of unfit animals include animals suffering pain (which is likely to be made worse by transport), animals with fractures or severe wounds, animals with prolapses and lame animals.
The Welfare of Animals (Transport) Order 1997 (Section 6) allows an unfit animal to be transported to the nearest available place of slaughter if the animal is not likely to be subject to unnecessary suffering by reason of its unfitness. The Fresh Meat (Hygiene and Inspection) Regulations 1995 (Part V, 17(2)(a)–(b)) require that the animal be accompanied by a written declaration by the animal’s owner, or person in charge of it, which is handed to the Inspector or OVS (Official Veterinary Surgeon) on arrival at the slaughterhouse, and which contains the information prescribed in Schedule 18 of the Regulations.
This is often referred to as the ‘Schedule 18 declaration’ and includes declarations regarding the animal’s identity, medicinal treatment it has received and signs of disease or injury exhibited. The decision of whether an animal is fit to travel is that of the owner. The Declaration does not have to be signed by a veterinarian. If a person certifies that an animal is fit to travel, but the Inspector or OVS at the abattoir thinks it was not, the person is open to prosecution because the animal is likely to have been caused unnecessary suffering.
Stocking densities in transit
There are commercial pressures to increase stocking densities. The more animals that can be carried on a transport vehicle, the less the average cost of transport per animal. The legislation prescribes appropriate space allowances. In general, animals should have enough space to lie down. For example, the loading density for pigs weighing around 100 kg should not exceed 235 kg/m2, equivalent to 0.425 m2/100 kg live weight. This is about the space needed by a pig to lie down in sternal recumbency. The legislation points out that in hot weather the space allowance may need to be increased by up to 20%. The reason for this is that pigs are very sensitive to overheating in hot weather and at high stocking densities they may be unable to cool themselves effectively. In the worst case they will die.
Transporting cattle at high stocking densities has also been shown to increase levels of bruising.
Mortality in transit
Death of an animal is the ultimate compromise of its welfare and results in total loss of value. The problem affects mainly pigs and poultry;
ruminants are generally more resilient. This is largely because of their different heat loss strategies. Pigs can only lose heat effectively by wallowing. In the UK pig deaths in transit (DOAs – dead on arrival) are particularly a problem above average daily temperatures of about 18°C.
This means that the number of deaths in transit is higher in the summer months. Mortality is also higher on longer journeys and in genotypes of pig that show greater stress susceptibility. Stress susceptibility in pigs is associated with the so-called Halothane gene (Hal+). The gene is present at relatively high frequencies in some breeds, notably the Belgian Pietrain, some strains of Landrace and meat-type hybrids, and is closely linked to genes that promote leanness and muscularity, so carcasses from these breeds have little fat and show desirable high conformation.
Overall, the average mortalities in transit in the UK are about 0.1% for pigs and 0.02% for sheep. These contrast with the much higher level (0.2%) found in broiler chickens.
Methods used to handle animals
Animals need to be moved from and into pens, along races and passageways and on to vehicles. Vehicles must have their own unloading system. Usually this is formed from the tailboard, which acts as an external ramp, and internal ramps to access the higher decks in multi-tiered transporters. Animals find negotiating steep (>20° to the horizontal) ramps difficult. In particular, pigs do not climb or descend ramps very easily or willingly. Some transporters are therefore fitted with hydraulic platform lifts instead of ramps. The legislation prescribes maximum angles for vehicle ramps: 29° for external and 33° for internal ramps. These are, however, far steeper than is realistic.
There are recommended ways of handling animals, in particular making use of their natural behaviour patterns. For example, sheep have a well-developed, strong following behaviour. The legislation prescribes that no excessive force may be used to move animals and there must be no lifting or dragging by the horns, legs, tail or fleece. Animals must not be hit with sticks. The use of electric goads is strictly limited: they may be used only on the hindquarters of cattle over 6 months old, or on adult pigs which are refusing to move forward when there is space for them to do so.
The shocks must be for no longer than 2 seconds and successive shocks must be adequately spaced out.
Poor handling can lead to animals slipping and falling and bumping into obstacles. This results in bruising or internal haemorrhages. By analogy with human experience, bruising is painful and therefore has
welfare implications. It also damages the appearance of a carcass and may therefore lead to downgrading. Extensive bruising may require trimming, leading to weight loss and therefore direct economic loss. Bruising is always higher in the carcasses from animals sold via live auction markets than in those sent directly from the farm to slaughter, partly because the handling they receive is often poorer and partly because they must be handled more.
Segregation of animals in transit
Some animals are naturally incompatible: if mixed they fight, leading to injury. A particular and common problem is fighting caused by the mixing of pigs that have been reared in separate pens. This is stressful to them and leads to unsightly lacerations on the carcass and poorer lean meat quality. The problem is commoner in entire males (boars) compared with gilts or castrates. Mixed groups of young bulls will also fight, leading to bruising and reduced meat quality. The Legislation specifies various animals that must be segregated during transport to prevent serious injury or suffering, including bulls over 10 months old unless reared in compatible groups or accustomed to one another.
Mixing of horned and unhorned cattle is generally proscribed and certainly not recommended.
Deprivation of food and water
Some period of food withdrawal before slaughter is desirable to reduce gut contents and therefore the chances of contamination of the carcass at evisceration if the distended gut is accidentally cut or broken. Pigs do not travel well on a full stomach, and mortality is higher in pigs fed too soon before loading. However, water should be available to animals at all practicable times. Long periods without food reduce live weights and carcass yields, a loss referred to as ‘shrinkage’ in North America. They also lead to hunger and hence poor welfare. A compromise therefore needs to be struck between the benefits and disadvantages of longer and shorter pre-slaughter fasting times.
PSE and DFD meat
PSE meat occurs in pigs. The meat is very pale, soft in texture (in the raw state) and exudative, meaning that it is wet in appearance and loses a lot of drip on cutting and during storage. The condition is caused by acute stress at slaughter, which speeds up the metabolism of the muscles, specifically glycolysis, immediately post-mortem. The resulting rapid acidification, at a time when the carcass is still hot, denatures some of the
muscle proteins so that they lose bound water, leading to the characteristic changes seen subsequently. A major cause of PSE is the stress associated with moving them through race-restrainer systems immediately before they are stunned if this is carried out thoughtlessly or with excessive coercion. However, even when handled carefully at slaughter, stress-susceptible pigs tend to produce a high frequency of carcasses that show PSE meat.
DFD meat can occur in all species. In cattle it is often referred to as Dark Cutting Beef (DCB). The meat is very dark in colour, firm in texture and dry or even sticky to the touch. DFD is caused by chronic stress pre-slaughter that depletes muscle glycogen levels. This limits the degree of glycolysis, and therefore acidification, post-mortem. DFD meat is therefore characterized by a high ultimate pH, so it tends to be prone to spoilage, partly because this high pH promotes bacterial growth, and partly because the deficiency of glycogen and other carbohydrates encourages the growth of bacteria that break down nitrogen-containing compounds such as proteins. This produces very unpleasant putrefactive smells. The high pH means that the proteins do not denature and retain their high water-holding capacity, so the meat surface is dry. Examples of stresses that cause DFD are prolonged food deprivation, transport fatigue and the fighting that often occurs between unfamiliar animals, especially pigs and young bulls.
Very occasionally, pig carcasses apparently show both PSE and normal, DFD and normal, or PSE and DFD characteristics in adjacent parts of the musculature. This is referred to as ‘two-toning’. It is difficult to explain in physiological terms but probably reflects differences in the inherent biochemistry of different muscles and how actively they have been used in the animal. So, red muscles, which have more oxidative fibres, tend to be prone to DFD and white muscles, which have a more glycolytic metabolism, are more susceptible to PSE.
Both PSE and DFD meat are discriminated against by consumers and have poor eating quality as well as appearance. They also both reflect poor animal welfare because they result from stress.
The spread of disease
The movement of animals from farm to slaughter has obvious implications for the spread of disease, particularly if they pass through one or more auction markets in the process. The stresses associated with handling and transport may additionally increase the animal’s susceptibility to infection by compromising the function of its immune system. When animals are held in lairage there is also the danger of rapid cross-infection of healthy individuals from infected ones by pathogens such as salmonellae. The spread of disease between animals may well compromise their welfare, and the spread of pathogens potentially compromises meat hygiene, and therefore quality.
Further Reading
Mcnally, P.W. and Warriss, P.D. (1996) Prevalence of carcass bruising and skin-marking between cattle bought from different live auction markets. Veterinary Record 140, 231–232.
Warriss, P.D. (1992) Animal Welfare – Handling Animals Before Slaughter and the Consequences for Welfare and Product Quality. Meat Focus International, July 1992, CAB International, Wallingford, UK, pp. 135–138.
Warriss, P.D. (1994a) Ante-mortem handling of pigs. In: Cole, D.J.A., Wiseman, J. and Varley, M.A. (eds) Principles of Pig Science. University of Nottingham Press, Nottingham, UK, pp. 425–432.
Warriss, P.D. (1994b) Ante-mortem factors influencing the yield and quality of meat from farm animals. In: Jones, S.D.M. (ed.) Quality and Grading of Carcass of Meat Animals. CRC Press Inc., Boca Raton, Florida, pp. 1–15.
Warriss, P.D. (1995) The welfare of animals during transport. In: Raw, M.-E. and Parkinson, T.J. (eds) The Veterinary Annual, vol. 36. Blackwell Scientific Publications, Oxford, UK, pp. 73–85.
Warriss, P.D. (1998a) Choosing appropriate space allowances for slaughter pigs transported by road: a review. Veterinary Record142, 449–454.
Warriss, P.D. (1998b) The welfare of slaughter pigs during transport. Animal Welfare 7, 365–381.
Warriss, P.D. (2000) Meat Science: an Introductory Text. CAB International, Wallingford, UK, 312 pp.
Warriss, P.D. (2003) Optimal lairage times for slaughter pigs. Veterinary Record153, 170–176.
Weeks, C.A., Mcnally, P.W. and Warriss, P.D. (2002) Influence of the design of facilities at auction markets and animal handling procedures on bruising in cattle. Veterinary Record 150, 743–748.