Examination of the bovine leukocyte environment using immunogenetic biomarkers to assess immunocompetence following exposure to weaning stress

Abstract

BackgroundThe molecular mechanisms by which stress induces the development of pathologies remains unclear, although it is recognised that one of the major factors affecting health as a consequence of stress is the involvement of the neuroendocrine system. In cattle, a number of necessary husbandry practices have been shown to activate the stress response, yet very little is known about the impact these have at the molecular level. The objectives of the study were to characterise, in male and female beef calves, the immune response to weaning stress in bovine leukocytes at the physiological and molecular levels and to assess the difference between calves weaned in the presence of the dam and those weaned and penned away from the dam.ResultsFollowing exposure to weaning stress, total neutrophil number and neutrophil:lymphocyte (N:L) ratio increased (P < 0.01) in calves. Additionally, expression of pro-inflammatory cytokine genes, including IL-1β, IL-8, IFN-γ and TNFα, were up-regulated (P < 0.01). Furthermore, there was increased (P < 0.001) expression of the glucocorticoid receptor, GRα, the pro-apoptotic gene, Fas and the Gram-negative pattern recognition receptor, TLR4. Calves penned away from the dam post-weaning had increased (P < 0.01) neutrophil number and N:L ratio compared with calves penned next to the dam, and female calves had higher (P < 0.05) expression levels of IL-2, IL-8, IFN-γ and TNFα than male calves.ConclusionsWeaning elicits an immediate and somewhat short-lived acute stress response in the calf. The effects serve to enhance, rather than suppress, the immune response by means of a heightened inflammatory response and cellular mobilization. The earlier and more profound increase in neutrophil number and N:L ratio together with reduced lymphocyte number in calves penned away compared with calves penned near their dams post-weaning suggests that the former may be more sensitive to weaning stress. The data also show a clear effect of gender in differential gene expression in response to stress with IFN-γ having increased expression in female calves compared with male calves over the course of the study. Additionally, this study has helped to characterise the inflammatory response to stress in calves and identify a number of novel candidate biomarkers suitable for investigation in future studies of stress.

Characterisation of haematological profiles and whole blood relative gene expression levels in Holstein-Friesian and Jersey bull calves undergoing gradual weaning

“…Weaning is typically a stressful event for suckled beef calves and this has previously been demonstrated by our group through the characterisation of haematological profiles of abruptly weaned suckled calves and manifested as an increase in neutrophil number, known as neutrophilia, and a decrease in lymphocyte number (lymphopaenia) (Hickey et al, 2003;Lynch et al, 2010;O'Loughlin et al, 2011). However, suckled calves undergo additional psychological stresses around weaning, which the artificially reared dairy calves in the present study were not subjected to, for example, breaking of the maternal bond and social grouping rearrangement.…”

“…A subset of eight H-F calves randomly selected from calves offered the M plane of nutrition and eight J calves randomly selected from calves offered the H plane of nutrition, were blood sampled for gene expression profiling, targeting genes previously found to be affected by weaning (O'Loughlin et al, 2011). These two treatment groups were chosen to examine the effect of breed on expression of the genes of interest, as energy intake and animal performance were similar.…”

“…Stress induced by abrupt weaning, maternal separation and transportation of suckled beef calves alters the immune response and increases susceptibility to fatal bovine respiratory disease (Hodgson et al, 2012). Our group has previously reported that abrupt weaning exerts an acute stress response in single-suckled beef calves, characterised by changes in the distribution of haematological cells (Lynch et al, 2010;O'Loughlin et al, 2011) and up-regulation in expression of genes involved in the pro-inflammatory response (O'Loughlin et al, 2011).…”

Biomarker responses to weaning stress in beef calves

“…Neutrophilia is one of the most frequently reported biomarkers of stress in cattle following weaning (Blanco et al, 2009;Lynch et al, 2011Lynch et al, , 2012O'Loughlin et al, 2011O'Loughlin et al, , 2012 and housing (Gupta et al, 2007;Hickey et al, 2003a). Gene expression of the potent neutrophil chemokine, CXCL8, was found to be up-regulated following transport (20-fold increase) (Gupta et al, 2007), castration (2-fold increase) (Pang et al, 2009) and weaning (2-fold increase) (O'Loughlin et al, 2011) and may account for distributional alterations in circulating neutrophils, serving to increase immune surveillance (Jones and Allison, 2007).…”

“…Gene expression of the potent neutrophil chemokine, CXCL8, was found to be up-regulated following transport (20-fold increase) (Gupta et al, 2007), castration (2-fold increase) (Pang et al, 2009) and weaning (2-fold increase) (O'Loughlin et al, 2011) and may account for distributional alterations in circulating neutrophils, serving to increase immune surveillance (Jones and Allison, 2007). Stress is reported to induce a response in a number of acute phase proteins (APP), including haptoglobin and serum amyloid A (SAA), with increased concentrations of APP demonstrated in calves following abrupt weaning (Hickey et al, 2003b;Martins et al, 2012) and housing (Alsemgeest et al, 1995).…”