Year of Publication

2019

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department

Animal and Food Sciences

First Advisor

Dr. Eric S. Vanzant

Abstract

Measures of temperament have been shown to influence physiological responses. Exit velocity (EV) has been identified as an objective, robust measure of temperament that can be used to predict subsequent performance of cattle. Additionally, previous studies from our lab indicate this measure of temperament may be related to production of interferon-γ (IFN-γ), a cytokine associated with cell-mediated immunity (CMI). Whereas research has investigated effects of EV upon immune responses, the overall goal of these studies was to examine this relationship under a variety of scenarios including human handling, transportation, and exposure to endophyte-infected tall fescue (E+) for determination of its ability to influence CMI in cattle.

In each of 5 experiments, calves were classified as either high or low EV animals, based upon measurements obtained prior to initiation of experimental periods. The hypothesis for these studies was that calves with high exit velocities would have lower systemic immune responses to applied treatments. Two experiments were designed to examine the relationship between exit velocity and lymphocyte IFN-γ production during and following a period of exposure to E+ seed and increased temperature humidity index conditions. Preliminary measures of this cytokine indicated a positive relationship with EV. During application of heat and E+ treatment application, no differences in IFN-γ production were detected between EV or endophyte treatment groups. However, in both experiments, after temperatures were returned to thermoneutral and E+ heifers were placed on the endophyte-free treatment, the positive relationship between exit velocity and total lymphocyte production of IFN-γ observed in baseline samples was reestablished. Similarly, during an experiment examining IFN-γ production by lymphocytes in steers during the 4 weeks following a 10h, 805 km transport study, average lymphocyte production of IFN-γ was higher and lymphocyte proportions producing IFN-γ lower in low EV steers, but total lymphocyte production of this cytokine did not differ between exit velocity treatments. In a grazing and finishing study, cattle were placed on E+ or novel endophyte pastures, with balanced representation of low and high EV treatments within each pasture. During the subsequent finishing period, blood samples for lymphocyte IFN-γ production were collected from a single high EV calf from each pasture group. Neither endophyte nor exit velocity was detected to be related with lymphocyte production of IFN-γ. In an experiment examining changes in cytokine gene expression changes during acclimation to human handling, IFN-γ, Il-6, IL-10, and IL-12 were observed to increase linearly over the experimental period in all calves, irrespective of exit velocity designation. In the same experiment, whole period pro-inflammatory tumor necrosis factor-α expression was higher for high EV calves, but interferon-γ (IFN-γ) was lower in this same treatment group. These studies, cumulatively, indicate EV may be related to systemic production of IFN-γ, but abrupt changes to an animal’s environment may serve to mask this relationship.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2019.033

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