The effect of reduced nocturnal temperatures on the performance of broiler chicks and hen turkey poults from 0 to 21 days of age
The world population has increased over the past century and with this increase in the world population comes an increase in demand of animal protein for consumption. The United States produced 8.78 billion broilers and 244 million turkeys in the year 2016 (USDA, 2017a,b). The production of broilers in the United States has increased by 1% from 2015 and turkey production is up 5% from 2015 (USDA, 2017a). One could speculate that these production values will continue to increase with an increasing world population. As the poultry industry grows, the usage of natural resources for energy will continue to increase and poultry operations need to become more energy efficient but in order to enhance energy efficiency, energy must be conserved without affecting yield or production yields must increase. The poultry industry is a vertically integrated system that uses contract growers to raise birds. This management system enables contract growers to assume less risk when raising birds by letting the companies that contract with them supply birds and feed while, contract growers supply the facilities to raise the birds and pay for the utility costs associated with raising birds which include electricity, gas, and water (May and Lott, 2001). While feed costs are the most expensive component in the production of poultry, the costs of utilities to raise birds should not be forgotten (May et al., 1998). Facilities for poultry production have improved with better insulation, ventilation, heating systems, and evaporative cooling, but there has been an increase in the expenditures for electricity and liquefied petroleum gas to allow for these improvements to be more effective in controlling the environment within facilities (May and Lott, 2001). The ability of facilities to maintain optimal environmental temperatures allow birds to have better feed efficient and therefore, reduces feed costs (May and Lott, 2000; May et al., 1998). Tabler and coworkers (2004) stated that energy costs consume approximately 25% of annual farm income of broiler operations and that heating costs are roughly four to five times the cost of electricity. Therefore, the ability to reduce heating costs would have the greatest impact on energy costs and overall profitability for contract growers depending on the operations location. Birds are homeotherms and can only maintain their body temperature within a narrow range of environments temperatures (Piestun et al., 2008) and therefore, regulate their body temperature by balancing heat production and heat loss. Heat loss occurs through respiratory evaporation and by convection or nonevaporative heat loss (Hillman et al., 1985; Wylie et al., 2001; Lin et al., 2005). Birds produce heat by their metabolism through feeding and muscle activity but also gain heat from their environment (West, 1965; Farrell and Swain, 1977). Feathers also help in thermoregulation by providing a layer of insulation which allows birds to retain more heat during periods of cold exposure and therefore, optimizes energy utilization and feed efficacy (Lesson and Walsh, 2004b). The ability to grow birds within their thermoneutral zone allows birds to perform as efficient as possible but intensive genetic selection for increased growth rate and feed conversion (Pereira and Naas, 2007) could have an impact on the thermoneutral zone of poultry. Temperature at which birds are raised has an impact on their performance and body composition; the optimum environmental temperature to raise birds has been researched by many (Howlider and Rose, 1987; May and Lott, 2001). Majority of research has been focused on high ambient temperatures effect on poultry production. High environmental temperatures have been known to increase mortality rates, decrease feed consumption, and lower body weights gains in poultry (Cooper and Washburn, 1998; Quienterio-Filho et al., 2010; Zhang et al., 2012). It has also been noted that high ambient temperatures can affect muscle yields, fat deposition and profile, muscle color appearance, and water retention which can affect the economic value of poultry products (Ain Baziz et al., 1996; McMurdy et al., 1996; Mckee and Sams, 1997; Wynveen et al., 1999; Molette et al., 2003; Petracci et al., 2004; Aksit et al., 2006; Zhang et al., 2012). Much research has been done in order to determine if birds have the ability to adapt to differing temperatures. Studies have looked at the effect of high or low incubation temperatures during embryogenesis in an effort to improve the acquisition of thermotolerance to high or low environmental temperatures post hatch (Tzschentke et al., 2001; Tzschentke and Basta, 2002; Yahav et al., 2004a,b; Piestun et al., 2008; Shinder et al., 2009). Birds may be able to thermal adapt to high or low environmental temperatures by a process of thermal conditioning during the early postnatal period (Yalcin et al., 2005). Studies have shown that thermal conditioning at an early age can improve thermotolerance to heat and cold stress, but this effort to acquire thermotolerance can have an effect on the performance and internal organs of the birds (Yahva and Hurwitz, 1996; Shinder et al., 2002). Cyclic temperature regimes have been studied in an effort to determine if birds benefit from periods of warmer and cooler environmental temperatures during different parts of the day (Waibel and Macleod, 1994). One management strategy that has not been researched in poultry, but has been studied in the swine model is the method of reduced nocturnal temperatures. Johnston and coworkers (2013) studied this management strategy in an effort to determine if it would be a viable option in reducing energy usage without affecting pig performance and therefore, making operations more economically efficient. One could suggest that reductions in nocturnal temperatures could potentially be an effective management strategy in an effort to reduce energy usage, greenhouse gas emissions, and production costs of poultry operations if birds' performance and health are not significantly altered.from Introduction.