Impact of transportation duration on stress responses in day-old chicks from young and old breeders

Transportation of livestock is regarded as a major source of stress and reduced welfare for the animals (Mitchell, 2009). Poultry, including day-old broiler chicks, are the only production animals that undergo transportation and associated stressors which may include handling, feed and water deprivation and thermal discomfort on the first day of their life (EFSA, 2011). In fact, piglets less than three-week old, lambs less than one-week old, and calves < 10-days old are considered unfit for transportation over a distance > 100 km (EU Council Regulation no 1/2005).

The early life environment and experiences during this transportation phase are crucial for the performance of chicks later in life (Decuypere et al., 2001, Jacobs et al., 2016, Mitchell, 2009, Valros et al., 2008). Therefore, recent studies and practices have started exploring the potential to transport incubated eggs instead of chicks to avoid fasting and other transportation-related stressors (Van Harn et al., 2013). Nevertheless, welfare or stress during post-hatch transportation and corresponding physiological responses have rarely been studied (Mitchell, 2009). Such information would facilitate the optimization of the transportation conditions and determine whether an alternative is warranted.

One method to determine the impact of transportation is to assess physiological stress responses. Plasma level of corticosterone (CORT) is a commonly-used indicator of stress in birds (e.g. Delezie et al., 2006, Kannan and Mench, 1996). CORT is the final effector of the hypothalamic–pituitary–adrenal (HPA) axis and participates in the control of the bird’s response to stress (Lin et al., 2004b). An increase of this hormone could therefore indicate that an animal is subjected to a stressor (Elrom, 2000). Furthermore, CORT has been linked to increased activity in feed-deprived, undernourished birds (6–8 week old chickens; Klandorf and Harvey, 1984), probably to promote foraging behaviour (adult passerine birds; Astheimer et al., 1992). Nevertheless, Wada et al. (2007) stated that young birds (in their case white-crowned sparrows) show resistance to stressors in order to minimize potential long-term negative effects of elevated glucocorticoids (e.g. depressed immune response).

A rise in plasma lactate or glucose can indicate physical exertion or stress (Delezie, 2006). In contrast, a decrease in lactate or glucose can be caused by feed deprivation (Buyse et al., 2002, Delezie, 2006, Wang et al., 2014). Lipid peroxidation could increase due to factors such as trauma, infection, and climatic stressors, resulting in oxidative stress and damage (Altan et al., 2003). A method to estimate oxidative stress is to determine plasma concentrations of thiobarbituric acid-reactive substances (TBARS), a by-product of lipid peroxidation.

Several studies indicate a difference in hormones and metabolites between chicks originating from young versus old parental flocks, possibly due to lower internal egg quality in old parental flocks (Decuypere and Bruggeman, 2007). Moreover, the age of parental flocks can positively affect performance, such as average daily gain, feed conversion and body weight (Jacobs et al., 2016), but may also negatively affect chick quality, which can be used as a predictor for growth (Decuypere and Bruggeman, 2007). Chick quality can be quantified with the method developed by Tona et al. (2003), which includes criteria for physical activity, dryness and cleanliness of down, retracted yolk, brightness and wideness of eyes, conformation and inflammation of legs, closure and colour of the navel area, and remaining membrane and/or yolk.

Several factors remain unknown, however, such as whether the impact of increasing transportation duration on day-old chicks depends on the age of their parents (and indirectly chick quality). If so, transportation duration may have to be adapted depending on parental flock age to avoid increased stress. Therefore, the aim of this study was to determine the interaction between transportation duration and parental flock age, by examining the impact of post-hatch transportation duration on physiological stress responses and quality in chicks originating from parental flocks of different ages.