G. L. Hahn

Thermoregulatory responses of feeder cattle

A study was designed to investigate the thermoregulatory responses of feeder cattle to both acute and chronic exposures to elevated environmental temperatures. Rectal temperatures (RT) and respiration rate (RR) showed significant differences between temperature treatments. Both RT and RR had a diurnal pattern, which followed the diurnal pattern of the ambient conditions with some lag. Heat production at thermoneutral conditions was significantly higher than at the heat stress treatments. Heat production and respiratory quotient were the only two parameters shown to change with acclimation to heat stress.

Characterizing animal stress through fractal analysis of thermoregulatory responses

Abstract Thermoregulatory responses, based on non-invasive tympanic temperature measures, are a logical energetically-based alternative to endocrine or other measures for objectively characterizing stress. Tympanic temperature datasets obtained from growing, ad-libitum -fed cattle ( Bas taurus steers) were used to compute the fractal dimension for thermoregulatory responses to a non-stressing and several heat-stressing conditions. Within defined limitations for sampling interval frequency, results showed clear differentiation among responses to the imposed environments by individual animals. Objective characterization of stress was attained and a threshold limit for stress defined using the technique.

CALCULATION OF FRACTAL DIMENSION FROM CATTLE THERMOREGULATORY RESPONSES

Abstract Fractal dimension analyses have previously been shown to objectively classify thermoregulatory responses of cattle to non-stressing and stressing thermal environments. This report presents a geometric method for calculating fractal dimensions ( D ) from time-series datasets of tympanic temperatures, and evaluates the effects of sampling intervals, recording system resolution and noise, and length of sample datasets on the calculated d -value. From these analyses, recommendations were developed for minimum temperature data resolution (0.16°C), sampling interval (3 to 15 min), and data set length (integer multiples of 24-h periods). To reduce the impact of ‘noise’ in the recording system to less than 5% change in the d -value, the number of errors times the magnitude of the errors (°C) should be limited to 0.64 when substituting for missing or questionable data. The fractal dimension computed using the prescribed technique with data collected according to the recommended criteria allows use of all collected data, without requiring removal of underlying deterministic functions or filtering of the data. The method is robust and provides objective differentiation of thermal stress levels in cattle, thereby serving as a basis for environmental evaluation and management.

Heat load management for feedlot cattle

Altering the microclimate by providing protection from the environment is one of the most useful tools helping animals cope with climatic conditions. For most feedlot cattle, facilities and management programs do not need to eliminate environmental stress completely, but rather minimize the severity of the environmental challenge and aid the animal in adapting to it. In addition to facility changes, dietary manipulation may also be beneficial for feedlot cattle challenged by environmental conditions. Studies conducted at the University of Nebraska demonstrate that programmed feeding systems significantly lower body temperatures during periods of heat stress. Programmed feeding systems involve management of feed intake pattern so as to eliminate or minimize simultaneous occurrence of peak metabolic and climatic heat loads. Tympanic temperatures were measured via thermistors placed in the ear canal and attached to data loggers. Cattle managed on programmed feeding systems for three to six weeks, maintained equal or lower tympanic temperature when compared with cattle fed ad libitum. The reduced tympanic temperature is likely due to a reduction in metabolic rate and a concurrent reduction in metabolic heat load. Greater long-term reductions in tympanic temperature likely occur if the cattle are on the programs for 1 to 2 weeks prior to the heat wave. Utilizing programmed feeding systems from late-June to early-August would appear to be sufficient to cover most heat waves.