**4. Heat stress and reproduction**

Studies have shown that high ambient temperatures, outside the thermal-neutral zone results to negative effects on chicken biological processes. The optimal temperature ranges between 12°C -26°C. Research findings presented in Ebeid et al. [35] suggest that reproduction of the animal is highly affected with high temperatures. The study shows that when white leghorn hens are subjected to high temperatures there is a decline in reproductive activity leading to reproductive failure and poor egg quality.

Fouad et al. [34] further showed that increased environmental temperatures affect all stages of semen production. Slight elevation of the environmental temperature during the early phase of semen production has been shown to stimulate testicular growth which in turn promotes increased quality and quantity of semen. However, high temperatures in mid and late semen production result in decreased the seminiferous epithelial cell differentiation which results a decrease in semen concentration and volume. This has negative impact on the cock's fertility and flock reproduction in general [34]. The work by Karaca et al. [36] confirmed that heat stress resulted to decreased semen quality.

Findings by Nidamanuri et al. [37] showed that the function of the hypothalamus and pituitary gland is negatively affected by heat stress. Results from a study [38] using leghorns chicken exposed to heat stress depicted a decline in the production of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH) which are associated with increased levels of prolactin. Rozenboim et al. [39] observes that the resulting low GnRH, LH and FH (follicle stimulating hormone causes regression of the ovary which reduces the capacity of the theca cells resulting in impaired steroidogenesis. Wasti et al. [11] indicated the levels of gonadotropinreleasing hormone, plasma progesterone, testerone and estradiol hormones is impaired in heat stressed birds which leads to a general reduction in reproductive efficency. The reduced effciency results in lost reproduction and subsequently poultry flocks productivity and profitability. It is further documented that eggs obtained from hens subjected to high temperatures have lower hatchability. High temperatures cause a decrease in granulosa cells responsiveness which results in the disruption of the hormones that are crucial in ovulation. Studies by Ayo et al. [40] and King et al. [41] involved collection of semen during summer to test the effects of heat on the characteristics of spermatozoa and found an increase in deformities including bent heads, cytoplasmic droplets and cut mid-piece. Ayo et al. [40] further demonstrated that semen collected during the cooler periods (especially in the morning) of the day resulted in higher rate of conception when used in artificial insemination.

The endocrine system and the environmental cues are the key drivers of reproductive patterns of an animal [42, 43]. There are various environmental factors that influence reproduction including the day length (more pronounced in temperate regions), temperature, rainfall patterns (seasons), human management practices such as feed and feeding management system, animal population interactions and socialisation, health and nutritional status of the individual among other factors [44]. Taberlet et al. [42] observed that significant alteration of one and/or a combination of the factors could partly or completely disrupt the reproduction function. The environmental factors that influence reproductive processes do so ultimately or proximately which is based on the time at which they affect the breeding activity. The ultimate influencers are more significant as they relate to the effects on long term basis. Food availability is the most important ultimate environmental factor that affects breeding due to the need to synchronise animal feed demand and supply. Ambient temperature is an important proximate environmental factor.

#### **5. The effect of heat stress on response to diseases**

The health of a flock has a direct relationship with poultry enterprise productivity and profitability. The costs and lost production associated with unhealthy flock leads to enterprise losses and at times to the collapse of the venture. There are a number of risk factors associated with the health of a flock including the climatic conditions of the area in which the production occurs [1]. Temperature is an important climatic factor that affects the bird's ability to fight off an infection. In order to resist or fight off an infection sufficient and high-quality nutrient are required [15]. The bird should also have minimal heat stress since there would be a

**195**

**6.1 Farm management**

*The Effects of Heat Stress on Production, Reproduction, Health in Chicken and Its Dietary…*

chicken thermal neutrality thus exposing the birds to diseases [45].

related to the higher incidences of heat stress in poultry flocks.

towards general farm management or dietary manipulation.

The primary objective of managing heat stress is to free up nutrients that would have otherwise gone into establishing and maintaining thermal neutrality in animals to be used in growth, maintenance of good health status, production and reproduction. This in turn lead to increased animal productivity and animal production enterprise profitability. The harmful effects of heat stress due to high temperatures are evident and therefore, it is necessary to adopt appropriate strategies to minimise the impacts of high temperatures and enhance production of eggs and chicken meat to meet the growing demand for poultry products [16]. Heat stress in poultry can be reduced by a multi-approaches strategy including modification of the surrounding environment (housing designs, ventilation systems, provision of shaded areas), nutritional management, stocking density management [51] and selection for heat tolerance genes [52, 53]. The approaches can be oriented

Designing well ventilated poultry house is the first step in the management of heat stress [15]. This can be achieved by installation of efficient air circulation systems in areas characterised by long periods of high ambient temperature. Butcher and Miles [54] notes that this not only ensures appropriate air movement in the poultry house in provision of sufficient air movement for convective heat loss

**6. Management of heat stress in poultry flocks**

competition for nutrients between fighting the infection and search for heat balance in the body. High temperatures negatively affect both the nutrients intake and the

High temperatures are commonly encountered in the tropics for most of the year and during summer in temperate regions. In sub-optimally managed flocks, the temperatures may rise above the thermal neutral zones thus stressing the birds and exposing them to diseases conditions [11]. This can be counteracted by housing the birds in well ventilated pens, provision of high-density nutrients diets and high

Heat stress compromises absorption of nutrients, integrity of gut wall and the immune system in birds [46, 47]. In addition, the weight of the liver reduced along with reducing levels of antibodies [48]. Another research found that the reduction of antibodies was could be the sole reason for increased incidences of diseases like infectious bursal disease virus (IBDV), Newcastle disease virus (NDV) and infectious bronchitis disease virus (IBDV) during heat stress in poultry birds [49]. High humidity alters the homeothermy in poultry birds and induces the growth of disease causing agents like viruses, fungi and bacteria [45]. Moreover, during hot conditions, incidence of many bacterial diseases such as salmonellosis, coccidiosis and *E. coli* infection increased [45]. It is also documented that broilers that were exposed to heat stress showed decreased immunity and became more susceptible to pathogens such as coccidia that induces necrotic enteritis [50]. Heat stress resulted in reduction of the relative weight of the thymus, Bursa of fabricius and the spleen which also suffered oxidative damage in exposed flock [34]. The decrease in the weight of the organs implied that the affected individuals suffered reduction in the production of antibodies. This results in higher exposure to infectious diseases in heat stressed birds. Wasti et al. [11] identified a spike in the prevalence of infectious and contagious diseases in poultry in summer seasons in the tropics which they

*DOI: http://dx.doi.org/10.5772/intechopen.97284*

level of diseases prevention technologies.

#### *The Effects of Heat Stress on Production, Reproduction, Health in Chicken and Its Dietary… DOI: http://dx.doi.org/10.5772/intechopen.97284*

competition for nutrients between fighting the infection and search for heat balance in the body. High temperatures negatively affect both the nutrients intake and the chicken thermal neutrality thus exposing the birds to diseases [45].

High temperatures are commonly encountered in the tropics for most of the year and during summer in temperate regions. In sub-optimally managed flocks, the temperatures may rise above the thermal neutral zones thus stressing the birds and exposing them to diseases conditions [11]. This can be counteracted by housing the birds in well ventilated pens, provision of high-density nutrients diets and high level of diseases prevention technologies.

Heat stress compromises absorption of nutrients, integrity of gut wall and the immune system in birds [46, 47]. In addition, the weight of the liver reduced along with reducing levels of antibodies [48]. Another research found that the reduction of antibodies was could be the sole reason for increased incidences of diseases like infectious bursal disease virus (IBDV), Newcastle disease virus (NDV) and infectious bronchitis disease virus (IBDV) during heat stress in poultry birds [49]. High humidity alters the homeothermy in poultry birds and induces the growth of disease causing agents like viruses, fungi and bacteria [45]. Moreover, during hot conditions, incidence of many bacterial diseases such as salmonellosis, coccidiosis and *E. coli* infection increased [45]. It is also documented that broilers that were exposed to heat stress showed decreased immunity and became more susceptible to pathogens such as coccidia that induces necrotic enteritis [50]. Heat stress resulted in reduction of the relative weight of the thymus, Bursa of fabricius and the spleen which also suffered oxidative damage in exposed flock [34]. The decrease in the weight of the organs implied that the affected individuals suffered reduction in the production of antibodies. This results in higher exposure to infectious diseases in heat stressed birds. Wasti et al. [11] identified a spike in the prevalence of infectious and contagious diseases in poultry in summer seasons in the tropics which they related to the higher incidences of heat stress in poultry flocks.
