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Title: Evaluating pen-day interactions in body temperature bilogistic mixed model for handling of feedlot heifers during heat stress

Author
item YANG, FAN - UNIVERSITY OF NEBRASKA
item PARKHURST, ANNE - UNIVERSITY OF NEBRASKA
item BROWN-BRANDL, TAMI
item EIGENBERG, ROGER
item NIENABER, JOHN

Submitted to: Applied Statistics In Agriculture Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/22/2010
Publication Date: 4/1/2011
Citation: Yang, F., Parkhurst, A.M., Brown-Brandl, T.M., Eigenberg, R.A., Nienaber, J.A. 2011. Evaluating pen-day interactions in body temperature bilogistic mixed model for handling of feedlot heifers during heat stress. In: Proceedings of Twenty-Second Annual Kansas State University Conference on Applied Statistics in Agriculture, April 2010, Manhattan, Kansas. p. 198-211. CDROM.

Interpretive Summary: Heat stress can be a serious problem for beef cattle in hot conditions. Understanding when and how heat stress occurs will help provide better ways to improve the well-being of animals. Body temperature is a good indication of animal stress level. Moving cattle during a hot day or for a long distance in the summer produces heat stress and may produce economic loss. Distance to be moved and environment are two of the most important factors that need to be considered when moving animals during hot periods. The process of handling and moving animals during hot periods in summer was evaluated using a seven-parameter model. During a hot environment, heifers moved the longest distance had a faster increasing and higher body temperature. The model accurately predicted the change in heifer body temperature during moving events.

Technical Abstract: 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 bilogistic mixed model is used to describe the dynamics of Tb during the moving event. Data was taken from heifers in pens located at different distances from the heifer work station on four separate summer days under hot conditions. This bilogistic 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 bilogistic mixed model for Tb with the above seven parameters, and to examine fixed and random effects from the cross-over experimental design. 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.