Non-Invasive Physiological Indicators of Heat Stress in Cattle

Abstract

Cattle are susceptible to heat stress, especially those kept on high levels of nutrition for the purpose of maximising growth rates, which leads to a significant heat increment in their bodies. Consequences include compromised health and productivity and mortalities during extreme events, as well as serious economic loss. Some measures of heat stress, such as plasma cortisol and temperature in the rectum, vagina, or rumen, are invasive and therefore unlikely to be used on farms. These may cause additional stress to the animal due to handling, and that stress in itself can confound the measure. Consequently, it is desirable to find non-invasive alternatives. Panting score (PS), cortisol metabolites in faeces, milk, or hair, and the infrared temperature of external body surfaces are all potentially useful. Respiratory indicators are difficult and time consuming to record accurately, and cortisol metabolites are expensive and technically difficult to analyse. Infrared temperature appears to offer the best solution but requires further research to determine the thresholds that define when corrective actions are required to ensure optimal health and productivity. Research in this area has the potential to ultimately improve the welfare and profitability of cattle farming.

Clinical Applications and Factors Involved in Validating Thermal Windows Used in Infrared Thermography in Cattle and River Buffalo to Assess Health and Productivity

“…This peripheral vascular and nervous network is known to respond to stressful or harmful stimuli. It is represented in Figure 3 , showing the location of the orbital region in the medial canthus of the eyelids [ 30 , 49 , 50 , 51 ]. These fibers are sensitive to neurosecretion of epinephrine and norepinephrine that promotes vasoconstriction in the capillaries, thus reducing heat exchange rate and functioning as a local thermoregulating mechanism [ 14 ].…”

Effort and Recovery in Nellore Oxen during Vaquejada Assessed with Ocular and Tail Infrared Thermography Superficial Temperature

“…The room temperature and relative humidity were measured by a thermohygrometer (Thermo-Hygrometer #7666.02.0.00, Incoterm Indústria de Termometers LTDA, Brazil), with a resolution temperature of 0.1˚C and an accuracy of +1˚C from 0˚C to 50˚C, the relative air humidity had a resolution of 1% (accuracy + 5%) during all evaluations for calibration and obtaining the normalized results. The emissivity for the readings was set at 0.95 ε, as described in the literature for cattle [14]. The thermographic images were processed in a specific program (FLIR Tools, FLIR Systems AB, Sweden) to receive adjustments compatible with the ambient temperature and relative humidity at the time of collection, and then it was possible to determine the maximum temperatures in the regions evaluated in all experimental phases in the respective periods of the day, providing greater reliability in the data collected [14].…”

“…The emissivity for the readings was set at 0.95 ε, as described in the literature for cattle [14]. The thermographic images were processed in a specific program (FLIR Tools, FLIR Systems AB, Sweden) to receive adjustments compatible with the ambient temperature and relative humidity at the time of collection, and then it was possible to determine the maximum temperatures in the regions evaluated in all experimental phases in the respective periods of the day, providing greater reliability in the data collected [14].…”

“…In the current experiment, the CLO evaluations, both in the control group and in the animals subjected to physical effort, showed low correlations with the environ-Open Journal of Veterinary Medicine mental temperature, which was expected because this measurement has been shown to be accurate in the evaluations with the IRT in different species. The core temperature of cattle is between 38.0˚C and 39.3˚C [14], and it is expected that temperatures found in CLO do not exceed those values in normal health and wellness.…”

“…This is a physiological process that occurs in animals that exerts physical effort produces redistributing blood in muscle tissues, providing nutrients and oxygen to skeletal muscle tissue [17]. According to Idris et al [14], the measurement of this parameter is quite efficient for determining variations in the behavior and metabolism of these animals because it is close to the hypothalamus, which is highly irrigated and has a fast and accurate response to the stressor. Under favorable conditions, when the stressor is removal, there is a rapid recovery of the normal CLO temperature.…”