Title : Effect of heat stress on physiological responses and milk production in dairy cattle using field-based THI observations in District Nowshera and Mardan, Pakistan
Abstract:
Background: Heat stress is a major problem for dairy cattle in Pakistan during the summer season. It negatively affects animal health, feed intake, and milk production. The Temperature-Humidity Index (THI) is commonly used to measure environmental heat load in livestock.
Objective: The objective of this study was to evaluate the effect of heat stress on physiological responses and milk production in dairy cattle under field conditions.
Methods: This field study was conducted on 850 lactating dairy cattle across 75 farms in District Nowshera and Mardan, Pakistan. The study animals included Holstein Friesian, Jersey, and crossbred cattle. I personally collected all field data during the study period. Environmental temperature and humidity were recorded to calculate THI for assessment of heat stress. Rectal temperature and respiratory rate were measured as physiological indicators. Milk yield and feed intake were recorded to assess production performance.
Results: Higher THI values were associated with increased rectal temperature and higher respiratory rate in dairy cattle. Animals exposed to heat stress showed reduced feed intake and a clear drop in milk production. Crossbred animals performed better under heat stress conditions compared to Holstein Friesian and Jersey cattle. Overall, increased environmental heat load had a clear negative impact on both physiological responses and milk production.
Conclusion: Heat stress, measured through THI, significantly affects physiological stability and milk production in dairy cattle under field conditions. Rectal temperature and respiratory rate are simple and useful field indicators of heat stress. The findings highlight the importance of proper management practices to reduce heat stress and improve dairy performance during hot weather.
Keywords: Heat stress, THI, Dairy cattle, Field study, Rectal temperature, Respiratory rate, Milk production, Pakistan
