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relationship amongst stress, temperament, and immune function in Brahman cattle
The studies described herein were designed to determine the influence of temperament on stress hormones and the immune system in response to various stressors. These stressors included transportation, lipopolysaccharide (LPS) challenge, and adrenocorticotropin (ACTH) challenge. In the first transportation study, bulls (8 Calm, 8 Intermediate, and 8 Temperamental) were loaded into a trailer and transported for 9 hr. Rectal temperature (monitored via indwelling recorders) increased within 0.5 hr of transportation, with greater peak rectal temperature in Temperamental than Calm bulls. Pre- and post-transport concentrations of cortisol and epinephrine were not affected by transportation, but were greater in Temperamental than Calm bulls. A second transportation study utilized 2 automatic sampling devices to allow the recording of rectal temperature and collection of blood samples, respectively. Rectal temperature was not affected by transportation or temperament in response to 4-hr of transport. Average heart rate oscillated between 60 and 130 bpm in Temperamental bulls, but remained around 100 bpm in Calm bulls. Transportation did not affect concentrations of epinephrine, although concentrations were greater in Temperamental bulls than Calm bulls. Cortisol concentrations increased in Calm bulls but not in Temperamental bulls in response to transportation. Additionally, there were limited effects of transportation on peripheral blood mononuclear cell proliferation, IgM production, and cytokine gene expression. Specifically, proliferation tended to be greater post-transport. Expression of the glucocorticoid receptor was, and the expression of toll-like receptor 4 tended to be, reduced post-transport, as analyzed by quantitative real-time RT-PCR. In a study utilizing a LPS challenge, basal stress hormone concentrations during the pre-challenge period were greater in Temperamental bulls than Calm bulls. However, in response to the LPS challenge, only the epinephrine response was influenced by temperament. Additionally, Temperamental bulls exhibited a smaller increase in rectal temperature and sickness behavior than Calm bulls. In the last study, change in gene expression in peripheral blood mononuclear cells in response to acute increases in cortisol was assessed. Plasma cortisol and gene expression of cytokines and the glucocorticoid receptor tended to increase in response to placement of jugular cannula. Additionally, administration of ACTH significantly increased plasma concentrations of cortisol and the gene expression of some cytokines (interleukin-4 and interleukin-10). This suggests that acute increases in cortisol may have positive effects on immune function in Brahman calves. Through an increased understanding of the interaction between the stress response and animal temperament, as well as how stress hormones and temperament influence immune function, animal management practices can be modified to reduce negative impacts on growth and productivity.
"Major Subject: Physiology of Reproduction"
Title from author supplied metadata (automated record created 2011-11-01 09:04:20).
Doctor of Philosophy Texas A&M University 2010 http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8254