Broiler chicken is the fastest growing meat type nowadays. Increased broiler’s growth rate increases their body heat production. When the body becomes overheated, a condition of heat stress exist which results in decreased growth rate primarily due to reduced feed intake (Hurwitz et al. 1980). Heat stress in birds cause suffering that leads to death and to reduce this problem of heat stress, heat production needs to be reduced, which can be done by evaporative heat loss through respiratory tract. Many other techniques have been developed to alleviate heat stress like upgrading the house padding (Nilipour 2000; Yahavet al. 2004), setting upcooling systemssuch as evaporative cooling (Donald 2000), reducing bird density, providing cool drinking water, and feeding birds during the cooler times of the day like in the morning hours or when the sun sets (Lott 1991; Yahav and Hurwitz 1996).
Minerals are essential for the naturalfunctioning of the body. Manganese, zinc, copper, calcium, and phosphorus are a few minerals that are important for the growth and development of bone (Watkins and Seifert 1997). Heat stress increases mineral excretion because digestibility is affected intestinal motility is increased (Smith 1987). El-Husseiny and Creger (1981) reported that heat stress decreases rates of calcium, iron, potassium, magnesium, sodium and zinc preservations in broilers. Similarly, Sahin et al. (2006) found that heat stress decreases tibial ash, calcium, phosphorus, and magnesium in quails. It also decreases length and widths of tibia, and promotes mineralization which in turn reduces bone strength of broilers (Vakili et al. 2010).
Heat stress also has negative effects on concentrations of potassium, sodium, phosphorus, copper, and zinc in serum. Their reduction is reported under heat stress conditions in broilers (Belay and Teeter 1996).Heat stress has also shown decreased iron, and chromium concentrations in serum. Heat stress also effects liver minerals and has shown reduction in the liver concentrations of iron, zinc, and chromium (Sahin et al. 2001).
As it is quite expensive to keep animal buildings cool, different methods of dietary manipulation are mostly considered. During heat stress, synthesis of vitamin C, E, zinc and chromium is decreased. So poultry diet is supplemented with these minerals due to their anti-stress effects (Sahin and Kucuk 2001). Melatonin supplementation also restores the decreased concentrations of vitamin C, vitamin E, vitamin A, Fe, Zn, Cu, Cr, in serum induced by heat stress (Sahin et al. 2004). Genistein supplementation is also helpful in increasing apparent nutrientdigestibility and bone mineralization. The reduced amount of minerals is excreted out of the body whereas the mineral concentration in tibia ash increases (Sahin et al. 2006). A supplemented dietincluding chromium at 1200 ppb can lessen the detrimental effects of heat stressed broiler. Feed intake, body weight and improved feed effectivenessincreases as a result of increased chromium supplement (Sahin et al. 2002). Another dietary practice to reduce heat stress of broiler is to supplement poultry feed or drinking water with various electrolytes which will increase their water intake. Addition of Dietary fibre in feed also has beneficial effects on broilers (Lee 1994). ASI supplementation (ASI; Arg =49.47%, silicone = 8.2%, inositol = 25%) considerably enhanced bone mineralization in quails and had no effect on weight gained, feed effectiveness and feed consumed (Sahin et al. 2006).During heat stress, KCl at level of 1.5% and NaHCO3 at level of 0.5%, improvedweight gain, and significantly increased serum potassium and bicarbonate level during heat stress. The results showed that combination of KCl and NaHCO3 supplementation decreased the negative effects of heat stress (Naseem et al. 2005).