Assessing thermal neutral zones in Sri Lanka for ten different dairy cattle breeds and crosses: An approach using temperature humidity index (THI)

The magnitude of heat stress in dairy cattle is assessed using temperature humidity index (THI) widely in the world. The present study was conducted to assess the appropriateness of incorporating THI in recommending dairy cattle breeds to different areas of Sri Lanka. The study considered 10 different cattle genotypes commonly reared for milk production in the country.  Daily THI values were computed by employing a thermal model, THI = Tdb - [0.55 - (0.55 × RH/100)] × (Tdb - 58) using data collected from 26 meteorological stations from 2005-2014. The THI values for different regions and the threshold THI values for milk production of 10 genotypes were used to produce THI maps. Among the crosses, Jersey crossbreds, except Jersey × Friesian cross, showed a high coping ability with comparatively high milk production capacity. Local cattle were not affected within the THI range observed in the country. THI based recommendation for distribution of dairy cattle could be made by identifying the variation of coping ability of cattle genotype and minimizing the vulnerability to climate change. Therefore, costly management interventions needed to mitigate the heat stress and related low productivity of dairy cattle under smallholder production systems could be abated. Key words: Climate change, dairy cattle breeds, heat stress.