cattle also attempt to mitigate the severity of heat stress by lowering the generation of metabolic heat. The
primary reason for a decline in feed efficiency is either a decrease in metabolic heat production or an increase
in energy expenditure for thermoregulatory processes.
[17]
Numerous detrimental effects on physiology,
behavior, productivity, reproduction, health, and well-being are examples of general reactions to temperature
stress. These consequences, therefore, must impact the quantity and quality of livestock products that may be
produced.
[13,18]
Furthermore, 20–30% of plant and animal species are likely to face an increased risk of
extinction as warming continues, with serious consequences for food security in developing countries.
[8]
Heat stress, particularly during the summer months, poses a significant challenge for the dairy sector. Rising
temperature and humidity have adverse effects on various aspects, including milk production, feed intake, feed
efficiency, reproduction, health, and even the growth rate of farm animals.
[19]
A significant challenge facing dairy
production is the instability of weather conditions attributed to global climate change. For cattle farmers
worldwide, heat stress is a significant concern. In 2015, a herd of 100 cows in the European Union was
associated with a loss of between 70 and 550 kg of milk daily compared with previous years. On the basis of
current milk prices, projected losses are expected to increase from an estimated US$670 million in 2014 to
US$2.2 billion annually by the end of the century.
[20]
The USA ranks among the top producers of cow's milk
globally, accounting for 14.2% of total production in 2014, according to statistical information from the FAO.
Following the USA are India, China, Germany, and Brazil. One factor contributing to the decline in milk
production is environmental variance.
[20]
Predicting heat stress is crucial for sustaining global milk production
levels, particularly in light of the geographical distribution of the largest producers of milk worldwide and the
increasing heat stress challenges encountered by dairy cows. However, a more significant concern for breeders
may be reproductive issues. Fertility, much like milk output, is also influenced by heat stress; however, issues
related to fertility are more difficult to identify and tend to become evident over time. Heat stress impairs
fertility, diminishes the effectiveness of insemination, and complicates the identification of estrus in cows.
Furthermore, heat stress increases the incidence of stillbirth, postpartum paralysis, calving problems, and
irritation of the uterine mucous membrane.
[21]
A negative energy balance can lead to decreased sperm
production in stud bulls, the formation of ovarian cysts, interference with germinal vesicle maturation, and
fluctuations in steroid concentrations, which may ultimately result in embryonic death.
[22]
Oxidative stress
negatively affects animal production when an animal is exposed to heat stress conditions. Additionally,
hyperthermia and other physiological abnormalities are among the detrimental consequences of heat stress in
dairy cows.
[23]
Therefore, it may be possible to prevent large financial losses caused by heat stress by identifying
specific genomes or gene markers related to heat tolerance and genetically selecting animals containing those
genes.
[24]
Heat stress has a detrimental effect on the health and biological functions of dairy cows, resulting in
decreased milk production.
[25]
Insulin resistance and mammary epithelial apoptosis, which are induced by
oxidative stress under heat stress conditions, are responsible for the reduced milk protein and casein
contents.
[26]
Therefore, identifying genes or genetic markers associated with heat tolerance and selecting
animals that carry them may help prevent large economic losses caused by heat stress.
[24]
3. Estimation of GHG using Isotopic and Nuclear techniques
Extreme weather events are becoming more frequent as a result of rapid global climate change in response to
rising anthropogenic GHG emissions. The average global temperature is increasing because GHGs are trapped
in the atmosphere; thus, the average global temperature of GHGs is increasing. Many nations struggle to
accurately identify the sources of GHG emissions and trace them back to their origins. This constraint makes it
difficult for countries to make evidence-based decisions to achieve the reduced emission objectives set by
international agreements such as the Kyoto Protocol and the Paris Agreement. By identifying the sources of
GHG emissions and quantifying their amounts, countries can strategically target the most significant sources of
pollution, thereby aiding in the achievement of climate change goals. Measurement and analysis of greenhouse
gas emissions are crucial for tracking progress toward global climate objectives and for minimizing carbon
footprints.
[27]
Capturing, using, lowering, and storing greenhouse gases, which are critical in problems such as
global warming and climate change, requires an understanding of their sources, emissions, measurements, and
management.
[28]
GHGs include various gases, but CO₂, CH₄ and N₂O emissions from agricultural sources play a
significant role in the overall increase in the GHG effect. Emissions of greenhouse gases, especially changes in
atmospheric concentrations, significantly impact global climate change. These GHGs are important because
they absorb infrared radiation from the Earth's surface, increasing the amount of energy that reaches the lower
atmosphere's surface, even though they make up a lesser portion of the atmosphere than nitrogen and
oxygen.
[29]
To determine the components and drivers of GHGs, stable isotopes such as
12
C and
13
C,
14
N and
15
N,
and
16
O and
18
O may be used.
[30]
These stable isotopes do not undergo radioactive decay and are primarily
measured using stable isotope ratio mass spectrometry (IRMS) to track mass-dependent fractionation
processes. The highest priority on scientific agendas worldwide is the measurement of GHGs released into the
atmosphere. The need to study hesitation when developing GHG emission inventories has increased alongside
increasing global concern and cooperation regarding climate change. The IPCC emphasizes the need to perform