Haematological and febrile response to Escherichia coli lipopolysaccharide in 12‐week‐old cockerels of genetically diverse layer lines fed diets with increasing L‐arginine levels
Due to birds’ lack of urea cycle key enzymes, chickens are unable to synthesize Arg de novo from ornithine (Tamir and Ratner, 1963) causing a direct interrelationship between the concentrations of plasma Arg and dietary Arg (Kwak et al., 1999). This amino acid is involved in multiple physiological processes, such as growth and feathering, plays a decisive role in protein biosynthesis and serves as precursor of various metabolites (reviewed in: Khajali and Wideman, 2010). In the avian immune system, Arg functions as only known precursor of nitric oxides (NO), which act as paracrine immune mediator and cytotoxic product of activated avian thrombocytes (St. Paul et al., 2012) and macrophages (Qureshi, 2003). The NO production is substrate limited by Arg (Sung et al., 1991). Depending on its secretagogue activities and its role as precursor of polyamines, Arg modulates further lymphoid organ development, proportions of peripheral blood leucocytes as well as proportions of T‐cell subpopulations after immune challenge (Kwak et al., 1999; Tan et al., 2014).
To induce an acute‐phase response in chicken, lipopolysaccharide (LPS) from cell wall of Gram‐negative bacteria is frequently used as immune stimulator (Xie et al., 2000; Tan et al., 2014). The following systemic inflammation is coordinated by the release of NO and the avian equivalents of pro‐inflammatory cytokines interleukin (IL)‐1β and IL‐6 from activated avian leucocytes (Staeheli et al., 2001). These immune mediators orchestrate the unspecific sickness behaviour characterized by anorexia and lethargy as well as increased hepatic secretion of acute‐phase proteins, alterations of body temperature and peripheral blood leucocyte proportions in chickens (Xie et al., 2000). During acute‐phase response in porcine (Luiking et al., 2005) and rodent sepsis models (Milakofsky et al., 1993), the plasma availability of Arg decreases, while an enteral Arg supply can be particularly advisable for the outcome of this process (Suchner et al., 2002).
As Kwak et al. (2001) and Van Eerden et al. (2004) have reported on variations in the Arg requirement and immune response of genetically diverse chicken breeds, we hypothesized that white and brown layer strains with varying daily egg mass production may respond immunologically differently to LPS‐induced systemic inflammation when ad libitum fed with diets of increasing Arg levels. Because the rearing period exposes layer‐type birds to a range of stressors influencing growth, metabolism and immunity as well as bird's later production efficiency, our objective was to examine the haematological and febrile response in 12‐week‐old cockerels of four purebred layer lines adapted to three levels of dietary Arg suffering from experimentally induced acute‐phase response.