The effects of weaning stress on the serum protein profile of calves : a proteomic analysis
Studies in animals and humans link both physical and psychological stress with an increased rate and severity of infections and onset of diseases. Stress is a very broad and complex topic. It can be defined as a condition occurring in response to adverse external influences capable of affecting physical health which leads to activation of a stress response in the body. There are two prominent stress responsive systems: the hypothalamic-pituitary-adrenal axis and the sympathetic adrenomedullary axis. These systems are responsible for the majority of the changes in the body, which occur in response to stress. Stress has been linked to many detrimental effects in cattle including immune suppression, increased disease susceptibility and decreased reproduction. These cause huge economic losses to the cattle industry every year. Weaning has been identified as one of the main stressors implicated in these negative effects. For this reason it is important to be able to identify animals stressed by weaning and do so using samples which are easily obtainable and useful for future diagnostic purposes. We hypothesize that weaning will cause sufficient stress in cattle to alter protein profiles in serum, which can be used to identify this type of stress. To do this we employed proteomic methodologies including two-dimensional gel electrophoresis and mass spectrometry to compare an abrupt weaned group of calves to a never weaned group and a previously weaned group (preconditioned). We have included a preconditioned group to examine the differences between this group and animals which have never been weaned. Preconditioned animals are typically used as a control group in weaning studies. A total of 83 distinct protein bands were identified after image analysis. Out of 83 protein bands, we found 9 spots which were significantly different in abundance among the treatment groups. Two out of 9 spots were significantly different between the abrupt weaned and the never weaned groups. Five protein bands were also found to be significantly different between the abrupt weaned group and the preconditioned group. Five protein bands were found to be significantly different between the never weaned group and the preconditioned group. Identification of these proteins, however, had limited success since the bovine protein database is not as extensive as that for humans or mice. Among the proteins identified were alpha-1-acid glycoprotein and collagen precursor. The differences in intensities found between the abrupt weaned group and the never weaned group may be useful as markers of calves going through weaning stress. We have also seen that animals who have undergone weaning and through the stress associated with that event are not exactly the same as animals which have never been weaned. This has implications to research where a preconditioned group is used as a control rather than a never weaned group. Despite the limitations of the methodology used for the current system, the overall results revealed specific changes in serum proteins which were associated with abrupt weaned animals. Future studies can be planned to determine the specificity of these protein changes and possibly identify the molecular basis of stress dependent disease susceptibility.
serum proteome, Weaning stress, biomarker
Master of Science (M.Sc.)