Evaluation of Thermal Indices as the Indicators of Heat Stress in Dairy Cows in a Temperate Climate

Abstract

Many thermal indices (TIs) have been developed to quantify the severity of heat stress in dairy cows. Systematic evaluation of the representative TIs is still lacking, which may cause potential misapplication. The objectives of this study were to evaluate the theoretical and actual performance of the TIs in a temperate climate. The data were collected in freestall barns at a commercial dairy farm. The heat transfer characteristics of the TIs were examined by equivalent air temperature change (ΔTeq). One-way ANOVA and correlation were used to test the relationships between the TIs and the animal-based indicators (i.e., rectal temperature (RT), respiration rate (RR), skin temperature (ST), and eye temperature (ET)). Results showed that the warming effect of the increased relative humidity and the chilling effect of the increased wind speed was the most reflected by the equivalent temperature index (ETI) and the comprehensive climate index (CCI), respectively. Only the equivalent temperature index for cows (ETIC) reflected that warming effect of solar radiation could obviously increase with increasing Ta. The THI and ETIC showed expected relationships with the RT and RR, whereas the CCI and ETIC showed expected relationships with the ST and ET. Moreover, CCI showed a higher correlation with RT (r = 0.672, p < 0.01), ST(r = 0.845, p < 0.01), and ET (r = 0.617, p < 0.01) than other TIs (p < 0.0001). ETIC showed the highest correlation with RR (r = 0.850, p < 0.01). These findings demonstrated that the CCI could be the most promising thermal index to assess heat stress for housed dairy cows. Future research is still needed to develop new TIs tp precisely assess the microclimates in cow buildings.

Perspective Chapter: Exploring Multifaceted Approaches to Enhance Dairy Cow Welfare

“…Values between 72 and 79 reveal mild heat stress, moderate heat stress is seen between 80 and 89, and values higher than 80 result in severe stress [41,52]. To estimate the heat or cold stress risk, some researchers promote the use of even more complex integrative indices, including the air temperature, relative humidity, and also wind/air draught speed, and solar radiation -Comprehensive Climate Index CCI [53].…”

Determining Heat Stress Effects of Multiple Genetic Traits in Tropical Dairy Cattle Using Single-Step Genomic BLUP

“…Low accuracies can occur for a number of reasons: (1) A small reference population (number of animals with genotype data); therefore, the reference population should be greater than 1000 to significantly increase the accuracy [64]. (2) In small populations with few animal genotypes, combining phenotypes, pedigree, and genotypes for a small subpopulation and a large population may increase the accuracy of genetic predictions [62,64]. (3) Altering the use of data from young bulls to proven sires will increase the accuracy, as in the proven sires, there are data records of daughters, whereas for young bulls, there are no such records available [63].…”

“…Against the background of a changing climate, heat stress significantly impacts the production, fertility, health, and welfare of livestock animals, including dairy cattle [1][2][3], in Thailand and in many other countries around the world [4][5][6][7][8]. In addition, increases in temperature and humidity have been affecting dairy cattle [1,2], leading to heat stress [3,9,10].…”

“…Against the background of a changing climate, heat stress significantly impacts the production, fertility, health, and welfare of livestock animals, including dairy cattle [1][2][3], in Thailand and in many other countries around the world [4][5][6][7][8]. In addition, increases in temperature and humidity have been affecting dairy cattle [1,2], leading to heat stress [3,9,10]. When subjected to heat stress, dairy cattle respond with reduced feed intake and rumination and increased water intake, as well as with a higher respiratory rate, increased sweating, more panting, and impeded energy balance [7,11,12].…”

The effect of animal-related and some environmental effects on daily milk production of dairy cows under the heat stress conditions

“…The first equations of the Temperature Humidity Index (THI), as a measure of HS, involving ambient temperature (AT) and relative air humidity (RH) were presented by Thom (1958), Kibler (1964), Berry et al (1964) and the National Research Council (1971). Using THI is a non-invasive way of detecting HS that can be easily calculated (Ouellet et al, 2019;Maggiolino et al, 2020) and provides opportunities for early detection of HS in dairy cows (Yan et al, 2021). Further development of THI indicators represents an important aspect of numerous studies (Sahin and Ugurlu, 2017; Wang et al, 2018;Ouellet et al, 2019).…”