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.

Unraveling the Genomic Association for Milk Production Traits and Signatures of Selection of Cattle in a Harsh Tropical Environment

“…The dairy cows in the present dataset are kept in production systems characterized by small herd sizes (ranging from two to eight cows per herd) and minimal investments towards farming system improvements. Furthermore, animals reared on family farms in tropical regions are often exposed to severe environmental stressors [21]. In contrast to most commercial farms and herds in developed countries, the majority of animals in the present dataset lacked intense management and nutritional interventions to enhance production and alleviate stress.…”

“…Furthermore, the comparatively large environmental variance compared to the additive genetic component indicates the challenging environmental conditions that were not captured by the statistical model effects. The inter-herd variations in milk yield due to feeding, breed, husbandry characteristics or cow treatments as identified in phenotypic trait analyses in Bengaluru [21] cannot be covered through the modeling of herd or SSI effects.…”

“…The animals reared in this region had favorable hygiene scores with mild variation across the rural-urban interface [20]. The farms were monitored for three seasons, "summer" (March-June), "monsoon" (July-October) and "winter" (November-February) [21,22], for cow trait recording and for genotyping. All the traits were recorded once per season.…”

Urbanisation threats to dairy cattle health: Insights from Greater Bengaluru, India

“…The problem of impaired cattle health was also encountered by small-scale dairy farmers in the cities of Karnal, Kolkata, and Guwahati (Sharma et al 2020 ). In addition, 10% of the interviewed farmers felt that poor housing conditions and space constraints were responsible for high shed temperatures, which can impair cattle health and provoke heat stress in cows (Pinto et al 2020b ; Velayudhan et al 2022 ).…”

“…As a result, many urban livestock keepers in so-called developing or transition countries tie up animals in open yards or on sidewalks of roads, or leave them scavenging in the streets during the daytime (Thuo 2013 ; Pinto et al 2021 ). In consequence, prolonged exposure to the sun, particularly during summer, leads to heat stress (Lees et al 2019 ; Velayudhan et al 2022 ).

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