Statistics, Department of


Date of this Version

Fall 12-2011


A Thesis Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Statistics, Under the Supervision of Professor Anne M. Parkhurst. Lincoln, Nebraska: December, 2011

Copyright (c) 2011 Fan Yang


Daily activities consume the energy of heifers, subsequently causing an elevation of body temperature, depending on the ambient conditions. A better understanding of the dynamics of body temperature (Tb) would be helpful when deciding how to process and handle heifers. It would also lead to specific recommendations on moving heifers under different ambient conditions, especially during the summer. In this study, a bi-logistic mixed model is used to describe the dynamics of Tb during the moving event. Data were taken from heifers in pens located at different distances from the heifer work station on four separate summer days under hot conditions. This bi-logistic model has seven biological parameters: initial body temperature, heat challenge rate constant, upper asymptote body temperature, challenge inflection point, baseline body temperature for recovery, recovery rate constant, and recovery inflection point. Pen and day were used as treatment factors in the model. Significant interactions between the factors were found for several parameters, indicating distance moved during the handling event influences the way an animal responds to a thermal challenge. The objectives of this study are to fit a bi-logistic mixed model for Tb with the above seven parameters, and to examine fixed and random effects. The main focus is to estimate and interpret the interactions between pens and days for the significant parameters to aid in management decisions involving when to work cattle.

Advisor: Anne M. Parkhurst