Effects of Heat Stress across the Rural-Urban Interface on Phenotypic Trait Expressions of Dairy Cattle in a Tropical Savanna Region

Abstract

Among all livestock systems in tropical regions, the dairy sector is facing huge challenges to sustain productivity under the rapidly changing climatic conditions. To date, there is a lack of knowledge on the combined effects of climate, season, and farm location on trait responses in different cattle breeds. Consequently, this study presents a novel approach to assess the impact of several climatic and geographical factors on production traits, energy efficiency indicators, and hygiene traits in dairy cattle reared across the rural–urban interface in the tropical savanna region of Bengaluru, a rising megacity in southern India. In total, 96 cattle were selected across Bengaluru’s rural–urban interface, reflecting a broad variety of social-ecological systems. The traits considered included test day milk yield (MY), body condition score (BCS), body weight (BW), hock assessment score (HAS), udder hygiene score (UHS), and upper leg hygiene score (ULHS). Apart from cow-related factors such as breed, lactation stage, lactation number, and milking frequency, the environmental classification variables of season, farm location (as expressed by survey stratification index, SSI), and temperature humidity index (THI) significantly affected most of the traits, with indication for breed-by-environment interactions. In particular, season significantly influenced production and hygiene traits. Furthermore, an evident breed variation was observed in the seasonal influence on BW, wherein exotic cows had a higher BW than crossbreds during the summer season. The distinct trend of SSI in its influence on most of the traits indicates that cows housed in urban areas had better trait expression than those in rural areas, thereby revealing a predominant role of management. The THI had a significant effect on MY, BCS, and HAS, and THI = 75 was identified as heat stress threshold. The results indicate the importance of considering ecological, social, and climatic factors simultaneously in order to improve primary and functional breed-specific traits of dairy cattle reared in challenging environments.