3. Mechanism

Mortality
Pain
Health status
Deprivation
Climatic stress
Fear
Further reading
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Mortality

Usually, mortality is indicated as DOAs (dead on arrival). This figure comprises both mortality during the journey and mortality in the lairage, as these are hard to distinguish. Mortality often is higher if transport distances are longer (Warriss et al., 1992a; Vecerek et al., 2006; Voslarova et al., 2007; Weeks et al., 2012a). Mortality will also be determined by the fitness of the flock and the temperature during transport.

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Pain

As end-of-lay hens usually have very brittle bones, the catching and crating can easily cause fractures. Also dislocations, bruises and wounds are often recorded. All of these cause pain to the birds. Apart from that old hens often have unhealed old breakages, which are likely to be painful during handling.

A survey by Sandilands et al. (2005) found that 26-55% of laying hens had sustained fractures during production and 4-25% had obtained fractures during depopulation depending on the housing system. These figures indicate that a large proportion of the birds are at risk of experiencing pain during depopulation and transport.

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Health status

European legislation dictates that birds that are not fit for travel, should only be transported if this would not cause an increase in suffering. As this cannot be realised for sick and injured birds, they should therefore be selected prior to transport. The catching crew should be instructed how to deal with unfit birds.

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Deprivation

Prior to transport birds are usually deprived of food. Water is always provided.

In general it is advised to start fasting laying hens in the morning of the day of depopulation. In practice there is a lot of variation in the timing of empty feeders, and thus the actual duration of food deprivation. In a Dutch study birds were deprived for an average of 18 hours before transport started (Van Niekerk et al., 2014). Including transport this was on average 28 hours, with extremes up to 43.5 hours. No clear legal limits are set, although several Codes of Practice do give directions as to what limits should be respected (see more details here).

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Climatic stress

Heat stress is thought to be the major contributor to both deaths (attributed to 40% of DOAs by Bayliss and Hinton, 1990) and overall transit stress in broilers. For laying hens the risks for heat stress is lower due to a usually bad feather cover. The degree of thermal stress experienced by birds in transit depends on the duration and intensity of both heat and cold stressors. In the UK risk for DOAs was increased by longer travelling distances and lower external air temperature (Weeks et al., 2012). Vecerek et al., (2006) indicted that hot summer weather or cold winter weather were associated with higher losses. Chauvin et al. (2011) pointed to rain and wind causing an increased risk of broiler DOA. Side curtains are used to reduce weather and climatological influences, but even in winter, these often restrict ventilation too much and excessive heat and moisture levels build up around the birds (Mitchell et al., 1992; Webster et al., 1992; Kettlewell et al., 1993; Burlinguette et al., 2012), leading to critical and lethal thermal conditions (Filho et al, 2008).

The birds experience climatological extremes during cold winter or hot summer climate, but also during the stationary parts of the transportation process (i.e. loading, unloading and waiting at the factory (Ritz et al., 2005).

Several studies indicated that there is a large variation in climate depending on the position on the truck (Webster et al., 1992; Kettlewell et al., 1993; Weeks et al., 1997; Richards et al., 2012). Especially naturally ventilated trucks mostly show this large variation. Studies of the aerodynamics of full-size and scale models of one design of vehicle, including a trailer, have shown that, when moving, air predominantly enters at the lower rear of the vehicle and moves forward to exit at the front (Baker et al., 1996, Hoxey et al., 1996). In certain positions there is virtually no air movement to dissipate the body heat produced by the birds. Weeks et al (1997) calculated that average air speeds immediately surrounding the birds in moving vehicles varied between 0.9 and 2.4 m per s with maxima of 6.0 ms-1. Based on data from loggers in eight positions within loads of end of lay hens transported in modules, Richards et al., (2012) confirmed that both when travelling and in lairage some parts of the load tracked outside air temperatures whereas others were dominated by bird heat. Conditions also varied within modules, with upper and central drawers unsurprisingly being warmer. Thermal ‘hot’ or ‘cold’ spots within loads may lead to deaths due to climatic conditions and excessive or inadequate ventilation (Hunter et al., 1997).

There are also large differences between conditions on moving and on stationary vehicles, again primarily due to ventilation and speed of air movement. Controlled and uniform ventilation in trucks therefore is essential. Vehicles fitted with both side curtains and roof-mounted inlet fans were generally able to maintain climate in the comfortable range (Weeks et al., 1997). These authors suggested air speeds within bird crates or modules should be maintained between 0.3 and 1.0 ms-1 except in extremely hot weather. Ventilation requirement is between 100 and 600 cubic metres per hour for typical commercial loads. Kettlewell et al. (2000) proposed that 2.2 m3.h-1 per kg of chickens was sufficient for uniformly ventilated loads in temperate conditions (up to 20 oC).
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Fear

Transportation is an extremely stressful process for commercial poultry. From a relatively calm and stable environment the birds are suddenly taken to an unknown situation, with various stressful stimuli such as noise, vibrations, deprivation of food and water, extreme climatological circumstances and high stocking densities. The greater the duration of exposure to stressors, the greater the integrated stress for the bird. The resistance of birds to handling (Zulkifli et al., 2000) and transportation stressors (Kolb and Seehawer, 2001) may be enhanced by adding ascorbic acid (vitamin C) to the drinking water.

Fear or stress reactions can be modified by changes in handling procedures. Jones (1992) found that the TI (tonic immobility) response (indicating fear) of both broilers and hens was reduced by gentle handling.

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Further reading (by language)

English

Mortality

Pain

  • Sandilands, V., Sparks, N., Wilson, S. and Nevison, I. (2005) Laying hens at depopulation: the impact of the production system on bird welfare. British Poultry Abstracts, 1, 23-24.

Climatic stress

  • Hunter, R.R., Mitchell, M.A. and Matheu, C. (1997) Distribution of ‘dead on arrivals’ within the bio-load on commercial broiler transporters: correlation with climatic conditions and ventilation regimen. British Poultry Science 38, S7-S9.
  • Kettlewell, P., Mitchell, M. and Meehan, A. (1993) The distribution of thermal loads within poultry transport vehicles. Agricultural Engineer 48, 26-30.
  • Richards, G.J., Wilkins, L.J., Weeks, C.A., Knowles, T.G. and Brown, S.N. (2012) Evaluation of the microclimate in poultry transport module drawers during the marketing process of end of lay hens from farm to slaughter. Veterinary Record, in press

Fear

  • Kolb, E. and Seehawer, J. (2001) Significance and application of ascorbic acid in poultry. Archiv fur Gerflugelkunde, 65, 106-113.

Czech

Mortality

  • Voslarova, E., Janackova, B., Vecerek, V. and Malena, M. (2007) Počty uhynulých slepic a kohoutů při přepravě na porážku v letech 1997 až 2006 (Numbers of hens and roosters that died during transport to slaughter from 1997 to 2006). In Ochrana zvířat a welfare Conference Proceedings. Brno: VFU Brno, pp. 186-188.
  • Voslarova, E. and Vecerek, V. (2015) Vliv vzdálenosti a ročního období na úhyn brojlerů a nosnic při přepravě na porážku. (Impact of transport distance and season on mortality of broiler chickens and laying hens transported for slaughter). In Drůbež 2015 Conference Proceedings, Brno: VFU Brno, pp. 11. (abstract)

Nederlands

Deprivatie

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