Recognition of Heat Stress in Dairy Cattle: Clinical Signs Relevant for Field Veterinarians

Heat stress in dairy cattle is frequently under-recognized in its early stages, despite having significant implications for production, welfare, and metabolic stability. It induces systemic physiological and cellular responses that can be identified through careful clinical observation (Scerri et al., 2023). 

Clinical signs in field conditions^1,2 

Veterinarians should focus on the following observable indicators: 

• Increased respiratory rate and persistent panting  

• Open-mouth breathing in advanced cases  

• Reduced feed intake and altered feeding patterns  

• Decreased rumination activity  

• Increased standing time and reduced lying behavior  

• Excessive salivation and signs of dehydration  

• Decline in milk yield as an early production indicator  

These signs reflect activation of thermoregulatory mechanisms and cellular stress pathways, including heat shock protein responses. 

Subclinical phase importance 

Before overt clinical signs appear, cattle may already experience^1,3: 

• Oxidative stress at the cellular level  

• Mitochondrial inefficiency affecting energy production  

• Early metabolic dysregulation  

These processes begin before visible physiological changes, making early detection critical. 

Clinical implication 

Diagnosis should rely not only on environmental temperature but also on behavioral and respiratory assessment. 

References  

1. Scerri TM, Lomax S, Clark CE. Bovine heat stress management: current amelioration approaches and the case for a novel mitogenomic strategy. Frontiers in Animal Science. 2023 Aug 25;4:1169743. https://doi.org/10.3389/fanim.2023.1169743  

2. Galán E, Llonch P, Villagrá A, Levit H, Pinto S, del Prado A (2018) A systematic review of non-productivity-related animal-based indicators of heat stress resilience in dairy cattle. PLoS ONE 13(11): e0206520. https://doi.org/10.1371/journal.pone.0206520  

3. Sigdel A, Abdollahi-Arpanahi R, Aguilar I, Peñagaricano F. Whole genome mapping reveals novel genes and pathways involved in milk production under heat stress in US Holstein cows. Frontiers in genetics. 2019 Oct 4;10:928. https://doi.org/10.3389/fgene.2019.00928