International Journal of Poultry Science 8 (8): 733-739, 2009 ISSN 1682-8356 © Asian Network for Scientific Information, 2009 733 The Effects of Ascorbic Acid and Seasonal Temperatures on Meat Quality Characteristics of Broiler Chickens Maintained in Open-Sided and Closed Houses I.T. Kadim*, B.H.A. Al-Qamshui, O. Mahgoub, W. Al-Marzooqi and E.H. Johnson Department of Animal and Veterinary Sciences, College of Agricultural and Marine Sciences, Sultan Qaboos University, Muscat, Sultanate of Oman Abstract: High ambient temperature is one of the prominent stressors that elicits low meat quality characteristics in broiler meat. The effect of ascorbic acid supplementation in drinking water on meat quality of broiler chickens reared in closed and open-sided houses during hot (ambient temperature 36 C) and cool o (ambient temperature 23 C) seasons were studied. Four hundred and thirty two, one-day-old chicks were o used for each house across the two seasons. Birds were maintained in 23 h light and 1 h dark cycles and offered ad libitum access to water and commercial broiler diets. Broilers in both houses were randomly subjected to four drinking water treatments (9 birds in each 6 replicates/treatment): 0, 100, 200 and 300 ppm ascorbic acid. Pectoralis muscles were taken at 24 h postmortem and analyzed for ultimate pH, expressed juice, cooking loss, Warner-Bratzler shear force value, myofibril fragmentation index, sarcomere length and colour. Pectoralis muscles collected during the hot season had significantly (p<0.05) higher pH, lower expressed juice, darker colour meat (L*) than those collected during cool season group. During the hot season, meat samples from chicken reared in an open-sided house had significantly (p<0.0) higher pH and lower lightness value (L*) than those reared in a closed house. Supplementation of drinking water with various levels of ppm ascorbic acid did not significantly improve meat quality characteristics of broiler chicken reared in open-sided or closed housing at high ambient temperatures. Key words: Seasonal temperature, ascorbic acid, meat quality, open-sided house INTRODUCTION The poultry industry constitutes an integral part of the Sultanate of Oman’s growing animal sector and is an important supplier of high quality protein. High ambient temperature is one of the main constraints confronting the poultry industry. Sensitivity of broiler chickens to heat stress is often a serious problem. Stress is manifested by increased motor activity and behavioral changes, accompanied by symptoms such as disturbances in respiration, blood circulation, hyperthermia, cyanosis and muscle rigidity (Ruiter, 1985). As a result of metabolic changes in the muscle, heat stress often results in a decrease in meat quality (Kadim et al., 2006; 2007; 2008a). Responses of birds to hot environments are in part mediated through changes in circulating levels of hormones, glucose, electrolytes and leucocytes and the function of organs (Blalock and Smith, 1985; Mitchell and Kettlewell, 1998). As the heat load increases, the resulting increase in body temperature will lead to tissue damage and release of intracellular vitamin and mineral components into the circulation (Whitehead and Keller, 2003). Much of the tissue damage, particularly those involving cell membranes, arises from lipid peroxidation which is enhanced in acute hot ambient temperatures. High ambient temperatures can also affect the quality of the meat by altering the physiology and metabolism of muscle (Northcutt et al., 1994; Froning et al., 1978). However, during the hot season, the poultry industry reports substantial losses in yield due to poor water-holding capacity, poor texture and pale colour (McCurdy et al., 1996). The loss of protein functionality due to extensive protein denaturation is considered to be the primary factor associated with low meat quality characteristics (Santos et al., 1994). While the adverse physiological effects of high temperatures might be lessened by measures such as increasing ventilation rate or the use of cooling devices, chronic exposure might be addressed through nutritional adjustments. High ambient temperature causes oxidative stress and impairs antioxidant status in vivo (Sahin et al., 2001; Whitehead and Keller, 2003). Lower plasma concentrations of antioxidant minerals and vitamins, such as vitamin C and increased oxidative damage have been observed in stressed birds (Feenster, 1985; Sahin et al., 2002). Antioxidant nutrient supplementation; especially vitamins C has been reported to attenuate the negative effects of environmental temperatures (Kafri and Cherry, 1984; Njoku, 1986). A previous study at our Animal Experimental Station revealed a beneficial effect of vitamin C supplementation on the performance of heat stressed broiler chickens (Kadim et al., 2008b). The objective of this study was therefore to ascertain whether ascorbic acid added to the drinking water during periods