Investigation of salivary acute phase proteins in calves

Abstract

Saliva is a colorless viscous liquid secreted from salivary glands that plays a major role in oral and general health. Saliva shares several compositional similarities with other body fluids e.g. blood and urine and is therefore interesting for biological assays (Lac et al., 1993). When compared to other biological samples as analytical matrix, saliva is advantageous for practical purposes due to its simple and minimally stressful, non-invasive collection. In addition to being more straightforward and economical to obtain than blood, saliva has the further advantage of being easier to handle for diagnostic purposes because it does not clot (Wong, 2006). The use of saliva for analytical purposes in mostly focused on clinical investigations (i.e. in the field of endocrinology, neuroendocrinology) and in physiological research (i.e. in sport and exercise science). Recent developments comprise proteomic and metabolomic analyses of saliva for identifying markers of disease (Lamy, 2012), however, the most frequent application of saliva analysis in praxi is probably the assessment of cortisol as a biomarker of stress. In veterinary medicine and in animal science, salivary cortisol is considered particularly important to assess welfare under different conditions of keeping and handling. However, besides cortisol, the use of saliva in veterinary science is still quite limited. With regard to acute phase proteins (APP) in animal saliva, the available literature is largely limited pigs and dogs. The APPs are blood proteins that can be monitored to assess the innate immune system’s systemic response to infection, inflammation, and trauma or stress (Ceron et al., 2005; Murata et al., 2004). Serum amyloid A (SAA), C-reactive protein and haptoglobin (Hp) have been identfied and quantified in porcine saliva and were demonstrated to be well correlated with the circulating concentrations (Gutierrez et al., 2009; Hiss et al., 2003; Hiss, 2009; Soler et al., 2012). To the best of our knowledge, there are no data available about the presence of APP in ruminant saliva. Alpha 1 acid glycoprotein (AGP), lipopolysacccharide binding protein (LBP), Hp and SAA have been reported to be expressed in bovine salivary glands (Lecchi et al., 2009; Lecchi et al., 2012; Rahman et al., 2010), thus their presence in saliva is probable and might be due to local expression and also to transfer from blood. In order to investigate the presence of four major APP, i.e. AGP, Hp, LBP and SAA in bovine saliva, we used samples collected from calves before and after dehorning. Dehorning of calves is a routine procedure carried out under local anesthesia with the purpose to facilitate management in later life. Dehorning is considered as stressful but the lesions are probably only mild since an acute phase reaction is reportedly not occurring (Doherty et al., 2007). Using quantitative assays for Hp as well as qualitative Western Blots (WB) for AGP, LBP and SAA, we aimed to evaluate whether these APP are detectable in saliva.