The immunological status of beef calves at birth & weaning as shown through gene expression of the toll-like receptor pathways

M.S. University of Hawaii at Manoa 2012.Includes bibliographical references.In order for Hawaii to promote a self-sufficient market for quality, island-raised beef, it is necessary for beef producers on the islands to optimize growth and health of their animals. It is well established that stress decreases an animal's health and growth rate (Klasing et al., 1987; Frisch, 1981; Fell et al., 1999). It is in the producer's interest to minimize stress and lower the risk of illness, thus improving growth. As weaning can be a highly stressful time for beef cattle, it is important to evaluate weaning procedures and the consequential effects on health and growth so that production can be optimized. By looking at an important signaling pathway of the immune system, called the Toll-like receptor (TLR) signaling pathway, we may be able to determine the impacts stress can have on the TLR signaling pathway when an animal undergoes stressful events such as birth and weaning. When pathogens invade and activate the TLR pathway it leads to an increase of inflammatory cytokines. These cytokines trigger immune defenses such as inflammation, fever, and phagocytosis in order to provide an immediate response against the invading pathogens. However, if not controlled and inflammation is prolonged, it can lead to a multitude of health problems for the animal both in the short and long term. An animal with a depressed immune system is more susceptible to disease, and can have poor growth as well as a reduced chance of survival during stressors such as weaning, transportation, or placement into feed lot environments. It would be beneficial to better understand what is happening immunologically in the neonate and during the actual stress event of weaning. Therefore, it is the goal of this research project to provide a base of understanding regarding the status of the innate immune system (TLR signaling in particular) at birth and subsequent changes associated with weaning. To further this understanding, both male and female beef calves were divided into three groups of early, standard, and late weaned animals. Blood samples were taken at multiple points to assess the gene expression of TLR-2 and TLR-4 pathways and amount of cytokine production at birth, and at pre-and post-weaning time points. Changes in expression will allow us to determine the status of the TLR Signaling Pathway at birth and also deduce the immunological impacts of weaning (Aderem and Ulevitch, 2000; Akira et al., 2001; Lee and Hwang, 2006). We hypothesize that newborn calves will have an overall pattern of upregulation of the TLR signaling pathway and that the TLR signaling pathway of smaller (earlier-weaned) beef calves will show overall upregulation compared with traditional and heavier (later-weaned) calves. As the first laboratory to utilize a novel 26,773 gene whole genome microarray developed for cattle, a major focus of this work is to collaborate with the company (Affymetrix ™) to validate and refine its use for future research. Measuring the expression of key mediators of the TLR pathway and other related cytokines will provide information with which we will be able to assess changes in the immune system. Initial expression data indicated that the majority of the genes of interest pertaining to innate immunology were upregulated primarily in the newborn sample pools, steadily declining to even out in expression between pre-and post-weaning sample pools