METABOLIC NETWORKS

Metabolic Networks

Metabolic Networks

Introduction

Birds are continuously confronted by a large number of stressors, including pathogens. Presently, the commercial poultry industry around the world faces rapid changes in housing and rearing practices, such as the banning of battery cages and prophylactic antibiotics that currently control environmental pathogens. These changes could increase the impact of stressors on bird health and welfare, and consequently reduce economic gains (Barnett and Hemsworth, 2003). Despite the variety, the overall effects of stressors are often similar. They induce an activation of the sympathetic-adrenomedullary (SAM) and hypothalamic-pituitary-adrenal (HPA) axes that result in the release of catecholamines and glucocorticoids, respectively. In general the aim of the stress previous response is to maintain or re-establish the homeostatic state and keep important physiological activities, such as production and reproduction, functioning normally (Siegel, 1995). Extensive studies on the stress physiology of poultry have emphasised that corticosterone produced during stress is one of the final hormones of the HPA axis. Corticosterone plays a multifunctional role through the alteration of endocrine and metabolic factors, including leukocytes and immune mediators.

Investigation of Metabolism Networks

For many years, researchers have investigated the effects of a variety of conditions in which birds live on their well-being and performance, including climatic, environmental, nutritional, physical, social, physiological, psychological, and pathological factors ([Thaxton and Siegel, 1970], [Davison and Flack, 1981], [Gross and Siegel, 1983], [Freeman, 1987], [McFarlane and Curtis, 1989], [Maxwell et al., 1992], [Scheele, 1997], [Puvadolpirod and Thaxton, 2000], [Post et al., 2003], [Cheng and Muir, 2004], [Mashaly et al., 2004], [Shini, 2004], [Hangalapura et al., 2005] and [Mumma et al., 2006]). These studies have shown that such conditions induce in poultry a state of chronic stress associated with an elevation in plasma corticosterone concentration, and a number of modifications to metabolic, physiological and immunological functions. Evidence is available that the immune status of previous chickens, as indicated by differential leukocyte counts or H/L ratios, can also be affected by bacterial stressors. These, like environmental stressors, cause an elevation in plasma corticosterone concentrations, and consequently increase H/L ratios due to leukopenia (lymphopenia) and heterophilia ([Harmon, 1998], [Nakamura et al., 1998], [Gehad et al., 2002], [Wang et al., 2003], [Shini et al., 2004] and [Shini et al., 2005]). Plasma corticosterone levels ([Freeman, 1980] and [Siegel, 1980]) and H/L ratios (Gross and Siegel, 1983 W.B. Gross and H.S. Siegel, Evaluation of the heterophil/lymphocyte ratio as a measure of stress in previous chickens, Avian Dis. 27 (1983), pp. 972-979. Full Text via CrossRef | | Cited By in Scopus (360)Gross and Siegel, 1983) that are used as short-and long- indicators of stress in birds could therefore be confounded by the involvement of bacterial LPS from a contaminated environment (Shini et al., 2007). In the present study, we address whether the previous response to non-infectious stressors differs from that towards bacterial stressors. If the previous responses do differ, it is important to then identify the pathways involved in both previous responses, and distinguish stress previous responses to non-infectious factors from the previous response to bacterial ...