Conference on Applied Statistics in Agriculture

USING NONLINEAR GROWTH CURVES TO ESTIMATE HEAT STRESS IN PROCESSING FEEDLOT CATTLE

Summertime heat waves cause excessive discomfort and, in extreme cases, death of feedlot cattle. During such emergencies, extension specialists are called upon for recommendations of management practices to minimize heat stress. Since moving cattle is believed to raise body temperature 1 degree, one recommendation is to move cattle before mid-day or reschedule to another day. More knowledge of body temperature dynamics could lead to more specific recommendations of how far cattle can be moved without stress. Several models are investigated - especially those involving exponential growth(challenge) and decay (recovery) such as the bi-exponential, single compartment and other models in pharmacokinetics. Data from feedlot trials can be "messy" and judgement calls involving starting and ending times, model parametrization, and statistical assumptions can influence the results. Analyzes from SAS: proc NLIN and checks on nonlinear assumptions are discussed.