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<p>Genetic selection of animals for climatic resilience is essential to improve the ability of cows to maintain higher productivity even under extreme environmental conditions. One of the most direct approaches to assess the impact of heat stress on livestock is by analysing decline in productivity, particularly milk yield. Modelling lactation curves using non- linear functions allows for an accurate estimation of milk loss attributed to environmental stressors. Various indices have been developed to quantify climatic stress, one of which is the Temperature Humidity Index (THI), widely used to integrate key environmental parameters reflecting the level of thermal discomfort experienced by animals. This study aims to quantify the loss in milk yield under such conditions and to derive three climate resilience indicators namely number of days in heat stress (NDHS), total milk loss during heat stress (TML), and average milk loss per animal per day during heat stress (AML) which reflect an individual animal’s ability to cope with climatic stress. Further genetic parameters of these derived resilience indicator traits, along with economically important production traits and their genetic and phenotypic correlations, were estimated using a multivariate animal model. A total of 132,512 daily milk yield records from 500 Sahiwal cows calved over 31 years were used in the study. The average milk loss during the first lactation of Sahiwal cows due to heat stress was estimated as 57.34 Kg with an average of 1.01 Kg/animal/day of heat stress. The Sahiwal cows on an average were in heat stress for 58.07 days during its first lactation. It was found that as the THI value exceeds 75, milk loss occurs at the rate of 0.1&#xa0;kg/unit of THI. The high yielders are susceptible to heat stress when the THI exceeds 71.34 while the medium yielders succumb to heat stress at the THI value of 74.29. Furthermore, the heritability estimates for the resilience indicator traits were found to be low to medium as the estimates ranged from 0.09 to 0.27. Additionally, there exists a strong correlation between NDHS and TML (0. 6447) and between the 305- day milk yield (MY 305) and TML (0. 37). These findings indicate that these resilience indicators not only aid in identifying more robust animals within a population but also support the development of targeted breeding strategies aimed at enhancing climate resilience, particularly in heat-prone regions.</p>

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Quantifying milk production losses due to heat stress in Indian Sahiwal cattle

  • 期刊论文

  • 发表日期：

    2026年5月29日

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  • P. Priyadharshini,
  • Alex Rani,
  • Gowane Gopal,
  • Phoebe C Lalremruati,
  • Vohra Vikas,
  • T. V. Raja

摘要

Genetic selection of animals for climatic resilience is essential to improve the ability of cows to maintain higher productivity even under extreme environmental conditions. One of the most direct approaches to assess the impact of heat stress on livestock is by analysing decline in productivity, particularly milk yield. Modelling lactation curves using non- linear functions allows for an accurate estimation of milk loss attributed to environmental stressors. Various indices have been developed to quantify climatic stress, one of which is the Temperature Humidity Index (THI), widely used to integrate key environmental parameters reflecting the level of thermal discomfort experienced by animals. This study aims to quantify the loss in milk yield under such conditions and to derive three climate resilience indicators namely number of days in heat stress (NDHS), total milk loss during heat stress (TML), and average milk loss per animal per day during heat stress (AML) which reflect an individual animal’s ability to cope with climatic stress. Further genetic parameters of these derived resilience indicator traits, along with economically important production traits and their genetic and phenotypic correlations, were estimated using a multivariate animal model. A total of 132,512 daily milk yield records from 500 Sahiwal cows calved over 31 years were used in the study. The average milk loss during the first lactation of Sahiwal cows due to heat stress was estimated as 57.34 Kg with an average of 1.01 Kg/animal/day of heat stress. The Sahiwal cows on an average were in heat stress for 58.07 days during its first lactation. It was found that as the THI value exceeds 75, milk loss occurs at the rate of 0.1 kg/unit of THI. The high yielders are susceptible to heat stress when the THI exceeds 71.34 while the medium yielders succumb to heat stress at the THI value of 74.29. Furthermore, the heritability estimates for the resilience indicator traits were found to be low to medium as the estimates ranged from 0.09 to 0.27. Additionally, there exists a strong correlation between NDHS and TML (0. 6447) and between the 305- day milk yield (MY 305) and TML (0. 37). These findings indicate that these resilience indicators not only aid in identifying more robust animals within a population but also support the development of targeted breeding strategies aimed at enhancing climate resilience, particularly in heat-prone regions.