# The Impact of Heat Load on Behaviour and Physiology of Beef Cattle: Preliminary Validation of Non-Invasive Diagnostic Indicators

## TL;DR

This study identifies subtle behaviors and physiological changes in beef cattle that can help detect heat stress without invasive methods.

## Contribution

The study introduces new non-invasive indicators of heat load in cattle based on limb movement, ear and tail positioning, and infrared eye temperature.

## Key findings

- Cattle showed increased respiration, panting, and infrared eye temperature during heat exposure.
- Left limb stepping and head, ear, and tail positioning were consistent indicators of heat stress.
- These indicators remained observable even during recovery from heat exposure.

## Abstract

Identifying heat load in feedlot cattle can be difficult, with the high density of cattle obscuring behavioural signs that might indicate the problem to workers. This study investigated changes in subtle behavioural cues such as lateralised limb movement, ear and tail positioning, and infrared eye temperature that could serve as early, non-invasive indicators of heat load in beef cattle. By confirming these indicators under controlled heat load conditions and distinguishing responses indicating heat load, the research offers a novel approach for preliminary validation of non-invasive diagnostic indicators for a precision livestock stress monitoring in high environmental temperatures.

Early diagnosis of heat load in beef cattle remains a challenge due to the limited understanding of behaviour-based indicators. This preliminary longitudinal study aimed to validate behavioural and physiological responses previously identified as heat load indicators. Black Angus steers were exposed to high environmental temperatures expected to cause heat load in the following sequence: an initial thermoneutral period, a hot period, and a recovery period. Changes in the positioning of key body parts, feeding behaviour, body maintenance, respiratory dynamics, and eye temperature were monitored. In the hot period, cattle increased their respiration rate, panting, and infrared eye temperature. Increased stepping by their left limbs suggested involvement of the right brain hemisphere in a stress response to high environmental temperatures. Cattle also held their heads more downward, ears backward, and their tail vertical, and reduced eating, grooming, and scratching during the hot period. Cattle responses to hot conditions were persistent in the recovery period, reflecting diagnostic relevance of the head, ear, and tail movements, stepping, especially by left limbs, and infrared eye temperature as non-invasive tools to identify heat load condition in cattle. The study reinforces our understanding of the specific behavioural and physiological responses to heat load condition, especially those involving left-limb stepping, ear and tail posture, and infrared eye temperature, are reliable indicators for identifying cattle experiencing high environmental temperature.