The fertility and reproductive efficiency of both male and female animals is very sensitive to climatic disturbances, particularly hyperthermia. The most evident consequences of heat stress are decreased quantity and quality of sperm production in males and compromised fertility in females. In this chapter, the effects of climate change on male and female reproduction have been separately and thoroughly elaborated. The effect of heat stress on embryo and fetal development has also been described. In the end, various approaches for mitigating the effects of heat stress on animals have been brought to light.
TopIntroduction
Animals play an exceptional role in the human population chiefly in the form of the products they produce, and this role has grown progressively during the last 40 years (McLeod, 2011). Despite rapid development in management and genetics, the reproductive performance of high producing animals has suffered a remarkable decrease (Royal et al., 2000; Lucy, 2001; López-Gatius, 2003).The blend of elements including temperature, humidity, rainfall, radiation, air movement, ionization, and atmospheric pressure constitutes the climate (Johnson, 1987). Every homoeothermic animal has an optimal ambient temperature zone (Thermo neutral Zone) within which the metabolic rate is at minimum (Yousef, 1985; Johnson, 1987) (Fig. 1). The comfortable range of environmental temperatures for the production or reproduction of most of the animals is between -0.5° and 20°C (Johnson, 1987; Vergaet al., 2007). However, over the past several decades due to anthropical and natural factors, the earth has been changing rapidly and there are predicted temperature increments of over 0.1-0.2ºC per decade (MacCracken et al., 2008), which has led toa significant increase in heat stress on human, animal and plant population (Lecha, 2007). One of the principal causes of low fertility in livestock is heat stress (Wolfensonet al., 2000) and it has been mostly studied dairy cattle (López-Gatius, 2003; Collier et al., 2006; Roth, 2008). Environmental temperature, relative humidity, wind speed, and radiation all contribute to the level of heat stress (De Rensis and Scaramuzzi, 2003). Elevated temperatures have negative effects on reproductive processes in both female and male animals (Das et al., 2016). In females, it leads to premature aging of the oocyte (Payton et al., 2004), reduced conception rate (Bridges et al., 2005) while in males it may lead to temporary or permanent infertility (Yaeramet al., 2006; Tusellet al., 2011). High ambient temperatures affect the sexual behaviour in animals (Bolocan, 2013; Graves et al., 2018; Boni, 2019). Heat stress may also lead to premature embryo loss in animals (Juet al., 2005). Consequently, heat stress is a general worldwide problem distressing 60% of the livestock population, which causes huge economic losses (Wolfensonet al., 2000). This is the reason why research in the last decades has been focused on ways to mitigate heat stress in animals (Ealyet al., 1993; West, 2003; Wolfensonet al., 1995).
Figure 1.
Thermal zones in animals (adapted from Yousef, 1985).