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Climate change is defined as an average weather condition of an area that is characterized by its own internal dynamics, and it can affect by changing its external factors. The United Nations Framework Convention on Climate Change (UNFCC) defines climate change as the change resulting from long-term direct and indirect activities that induce changes in the compared time, which are much more than the natural change (UNFCCC, 1992). On the other hand, the weather is a set of all the phenomena occurring

The global carbon emission rate, due to energy-driven consumption of fossil fuels and anthropogenic activities, is higher at any point in mankind history, disrupting the global carbon cycle and contributing to a major cause of warming of the planet with air and ocean temperatures, which is rising dangerously over the past century. Climate change presents challenges both direct and indirect for livestock production and health. With more frequent extreme weather events including increased temperatures, livestock health is greatly affected by resulting heat stress, metabolic disorder, oxidative stress, and immune suppression, resulting in an increased propensity for disease incidence and death. The indirect health effects relate to the multiplication and distribution of parasites, reproduction, virulence, and transmission of infectious pathogens and/or their vectors. Managing the growing crossbreeding livestock industry in Bangladesh is also at the coalface for the emerging impacts of climate change, with unknown consequences for the incidence of emerging and re-emerging diseases. Bangladesh is now one of the most vulnerable nations to global climate change. The livestock sector is considered as a major part of food security for Bangladesh, alongside agriculture, and with one of the world’s largest growing economies, the impacts are exaggerated with this disaster. There has been no direct study conducted on the impact of climate change on livestock health and the diseases in Bangladesh. This review looks to explore the linkage between climate change and livestock health and provide some guidelines to combat the impact on livestock from the Bangladesh perspective

The effect of climate change on animal health may be either direct or indirect (Figure 1) and may be due primarily to changes in environmental conditions, which include air temperature, relative humidity, precipitation, and frequency and magnitude of extreme events (i.e., heat waves, severe droughts, extreme precipitation events, and coastal floods). Although this article focuses on the effects of environmental factors, it should be noted that factors leading to the effects of climate change on health are extremely complex, involving not only environmental forces, but also ecological and social aspects, economical interests, and individual and community behaviors (Forastiere, 2010).

Figure 1.
Schematic representation of the impact of climate change on animal health.
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Schematic representation of the impact of climate change on animal health.

The direct effects of climate change on health include temperature-related illness and death. Indirect impacts follow more intricate pathways and include those derived from the influence of climate on microbial density and distribution, distribution of vector-borne diseases, food and water shortages, or food-borne diseases (Lacetera et al., 2013). The aim of this article is to summarize the current state of knowledge regarding the influence of climate and climate change on the health of food-producing animals.

Direct Effects
The direct effects of climate change on health may be due primarily to increased temperatures and frequency and intensity of heat waves (Gaughan et al., 2009). These effects are mediated by induction of heat stress conditions. Depending on its intensity and duration, heat stress may negatively affect livestock health by causing metabolic alterations, oxidative stress, immune suppression, and death (Figure 2).

Figure 2.
Schematic representation of the most frequent consequences of heat stress on animal health.
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Schematic representation of the most frequent consequences of heat stress on animal health.

Metabolic Disorders
Homeothermic animals respond to high temperatures by increasing heat loss and reducing heat production in their attempt to avoid increased body temperature (hyperthermia). Such responses include an increase in respiratory and sweating rates and a decrease in feed intake. These physiological events may provide a significant contribution to explain the occurrence of metabolic disorders in heat-stressed animals (Figure 3).

Figure 3.
Schematic representation of some mechanisms through which heat stress may cause metabolic disorders in farm animals.
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Schematic representation of some mechanisms through which heat stress may cause metabolic disorders in farm animals.

Heat stress can contribute to the occurrence of lameness in dairy and beef cows (Shearer, 1999). Lameness in cattle may be defined as any foot abnormality that causes an animal to change the way that it walks. Lameness can be caused by a range of foot and leg conditions, themselves caused by disease, management, or environmental factors and is one of the most significant health, welfare, and productivity issues. The contribution of heat stress to lameness is perhaps due to ruminal acidosis or increased output of bicarbonate (Cook and Nordlund, 2009). Heat-stressed cattle eat less frequently during cooler times of the day, but they eat more at each feeding. Reduced feed intake during the hotter part of the day, followed by increased feeding when the ambient temperature cools down, can cause acidosis which is considered a major cause of laminitis (Shearer, 1999). As ambient temperatures rise, the respiratory rate increases with panting progressing to open-mouth breathing. A consequence is respiratory alkalosis resulting from a rapid loss of carbon dioxide. Cattle compensate by increasing urinary output of bicarbonate. Rumen buffering is affected by a decreased salivary bicarbonate pool. Lameness, with sole ulcers and white line disease, will appear in a few weeks to a few months after heat stress.

The reduction of feed intake combined with increased energy expenditure for maintenance may alter energy balance and explain why heat-stressed animals lose body weight and/or mobilize adipose tissue during heat stress. In particular, during summer, early lactating dairy cows are more likely to experience subclinical or clinical ketosis (Lacetera et al., 1996) and are at higher risk to develop liver lipidosis (Basiricò et al., 2009). Ketosis is a metabolic disease that occurs when the animal is in a severe state of negative energy balance, undergoes intense lipomobilization, and accumulates ketone bodies, which derive from incomplete catabolism of fat. Liver lipidosis is another consequence of the intense mobilization of fat from adipose tissue. Compromised liver function in heat-stressed cattle is testified by reduced albumin secretion and liver enzyme activities (Ronchi et al., 1999).

Oxidative Stress
In farm animals, oxidative stress may be involved in several pathological conditions, including conditions that are relevant for animal production and the general welfare of individuals (Lykkesfeldt and Svendsen, 2007). Oxidative stress results from an imbalance between oxidant and antioxidant molecules and may depend on the excess of oxidant and/or lack of antioxidant substances (Figure 4). In the last 10 to 15 yr, the involvement of heat stress in inducing oxidative stress in farm animals has received increasing interest (Bernabucci et al., 2002; Akbarian et al., 2016). The total antioxidant status concentrations in serum of heifers were lower in the summer than in the winter in peri- and postpartum periods (Mirzad et al., 2018).