Effect of simulated long transport on behavioural characteristics in two strains of laying hen chicks

Abstract

Newly hatched chicks are routinely subjected to varying durations of transport shortly after hatching. Because little is known about the effects of this putative stressor on behavioural development, the present experiment tested for the effects of a simulated long transport-like treatment during the first day of life in two strains of laying hen chicks on growth, the development of perching behaviour, fear of humans (measured as the duration of tonic immobility induced by manual restraint) and the willingness to compete for access to feed. Fourty newly hatched Hy-Line W-36 (W-36) and 40 Hy-Line Brown (HB) chicks distributed over two blocks were subjected either to a short duration of handling and transport prior to delivery at the laboratory (SHORT treatment; duration of 4 h) or to the same treatment plus an additional period of intermittent movement used to simulate longer transport (LONG treatment; duration of 14 h).

LONG birds started perching at a significantly earlier age than SHORT birds (P < 0.01), but strain effects on the duration or frequency of perching were non-existent or sporadic. W-36 birds had a longer duration of tonic immobility than HB birds (P < 0.001) but there was no effect of the treatment (P > 0.10). The treatment reduced the birds’ willingness to compete for feed (P < 0.02), but this was mainly due to an effect on W-36 birds, as indicated by an interaction between treatment and bird strain (P < 0.02). The results thus indicate that the LONG treatment reduced the age at which birds first used perches and reduced the willingness to compete for feed. However, as these results were rather sporadic we could not show that the long transport-like treatment of day old chicks has wide-reaching effects on behavioural development. Further studies are needed to assess the long-term effect of transport duration on chicks and laying hens.

Introduction

A large body of research in chickens indicates that the early environment is crucial for the development of later behaviour. Different studies document effects of exposure to novelty (Jones, 1997), human contact or handling (Grigor et al., 1995, Fluck et al., 1997), environmental enrichment (Jones, 1982), cold stress (Davis and Fischer, 1978), mechanical restraint (Marin et al., 2001) and access to perches (Gunnarsson et al., 2000). However, there is no information about how exposure to long durations of transport in day old chicks might affect their subsequent behaviour. This is important because conventional layer and broiler chicks are handled in connection with sorting, sexing, immunization and packaging, and then transported over rather long distances for delivery to the farm. According to current EU legislation pullets can be transported for a maximum of 24 h and chicks may be held without access to feed or water for up to 72 h post-hatch. Although this legislation is based on the fact that chicks can survive on metabolic reserves stored in their yolk sack for up to 3 days, it is possible that exposure to long durations of transport without access to feed or water may cause some stress in chicks and adversely affect their development.

Different laying hen strains may differ in their behaviour and the ability to cope with stressors (Klein et al., 2000, Hocking et al., 2004). For example, Webster (1995) found that Hy-Line W77 hens were more adversely affected by a short period of fasting than Hy-Line brown hens, suggesting that these white birds may have a higher sensitivity to metabolic perturbations than the brown birds. Anecdotally, producers often report differences between different lines. They suggest that Hy-Line white hens are more flighty than Hy-Line brown hens and that ISA brown hens have a higher tendency to feather peck than ISA white hens. Brown Hy-Line hens have also been said to be less prone to use perches that white Hy-Line birds. The effects of stress may therefore be expected to depend on the strain's genetic constitution.

The aim of this experiment was therefore to study the effect of the stress caused by a prolonged transport-like treatment on the behaviour of two strains of commercial laying hen chicks. The treatment was meant to provide a standardized application of some of the conditions causing stress during transportation, including prolonged feed and water restriction, novelty, confinement and intermittent movement. The strains were selected from the same breeding company but represent slightly differing breeding goals. The Hy-Line W-36 (W-36) is mainly used for production using cage housing, whereas the Hy-Line Brown (HB) is used for production using both cage and floor systems (http://www.hyline.com/). The W-36 also has a slightly higher feed conversion ratio than the HB (ibid), a factor that has previously been shown to influence the ability to cope with stressors (Braastad and Katle, 1989, Beilharz et al., 1993, Beilharz and Mitpaiboon, 1994).

Our arguments for choosing to test for effects of a long duration of simulated transport on growth, fear of humans induced by manual restraint (tonic immobility), the ability to compete for access to feed in hungry chicks and the development of perching behaviour are given in the following. In general we predicted that if the treatment was detrimental to chick development it should decrease growth rates, increase fearfulness, reduce the ability of chicks to compete and reduce the development of perching behaviour. Growth was chosen as a response variable because stress may inhibit insulin-like growth factor-I secretion and negatively affect growth (Vance et al., 1992, Kakizawa et al., 1995, Bruggeman et al., 1997). We measured the duration of tonic immobility in response to manual restraint because of evidence that the duration of tonic immobility increases in chickens exposed to stress (Jones, 1986), possibly because of exposure to elevated levels of endogenous corticotrophin releasing factor (Adamec et al., 1991). Competitive responses were measured because stress may inhibit the production of gonadal steroids such as testosterone (Rivier and Rivest, 1991) and because low levels of testosterone may attenuate aggressive and competitive responses. Perching is important for the welfare of birds (Gunnarsson et al., 1999, Gunnarsson et al., 2000) and depends on coordinated cognitive and motor development (Gunnarsson et al., 2000). Furthermore, previous experiments show that stress may impair cognitive processes (De Kloet et al., 2005, Hage et al., 2006) and could therefore impair the development of normal perching behaviour in chicks.