Abstract
ABSTRACT The objective of this study was to evaluate the performance and carcass yield of broilers submitted to heat stress during different rearing stages. A total of 840 one-day-old CobbAvian48TM male broilers were housed in an experimental house equipped with conventional ventilation system and foggers. Birds were distributed according to a completely randomized design into four treatments, with six replicates of 35 birds each. The treatments consisted of: T1 (control) - birds reared under natural temperature and relative humidity conditions from 1 to 42 days of age; T2 - birds submitted to heat stress (HS) from 16 to 21 days of age; T3 - birds submitted to HS from 22 to 42 days of age; and T4 - birds submitted to HS from 16 to 42 days of age. Birds were submitted to heat stress daily for one hour (12:00-13:00h).On day 42, performance data were determined. Six birds per replicate were selected and sacrificed to obtain carcass, parts, and giblet weights and yields. Performance parameters were not influenced by the treatments. Broilers submitted to 1-h cyclic heat between 16 and 42 days of age presented lower deboned breast weight compared with those maintained in natural temperature and relative humidity conditions. It was concluded that the performance of broilers submitted to short cyclic heat periods is not impaired.
Highlights
Factors such as temperature and air humidity induce changes in bird homeostasis (Lin et al, 1996; Yahav et al, 2004)
The poultry house was made of a masonry and metal structure, fiber cement roof, concrete floor covered with wood-shavings litter, open sides covered with plastic canvas curtains, and equipped with foggers and ventilation fans
The environmental temperature (ET) means recorded during the heat-stress period on days 16-21, 22-28, 29-35 and 36-42 were, respectively, 25.4 °C, 27.8 °C, 26.9 °C and 24.9 °C for the control group, 26.7 °C, 26.1 °C, 26.0 °C and 24.3 °C for the group submitted to heat stress between 16 and days, 25.3 °C, 24.9 °C, 26.5 °C and 24.4 °C for those submitted heat stress between and 42 days and 25.0 °C, 26.5 °C, 26.6 °C and 22.5 °C for those submitted to heat stress between 16 and 42 days of age. These means did not differ from the handbook recommendations for male CobbAvian48TM broilers
Summary
Factors such as temperature and air humidity induce changes in bird homeostasis (Lin et al, 1996; Yahav et al, 2004). Birds above the thermoneutral zone increase heat dissipation to maintain thermal balance. Broiler chickens’ growth, development (Mazzi et al, 2002) and performance (Borges et al, 2003) are impaired under these thermal discomfort conditions, fact that leads to economic losses in the breeding activity. The exposure to high ambient temperatures is acknowledged for having negative effects on carcass (Oliveira et al, 2006a; Oliveira et al, 2006b) and noble cut yields (Oliveira et al, 2006b). These losses take place because elevated temperatures change energy retention, protein and fat deposition in the carcass, as well as viscera growth (Baldwin et al, 1980). Reduced feed intake (by 12.4% and 28%) and decreased weight gain (by 18% and 44%) are among the adverse effects from heat stress recorded for birds bred at 30°C and 35°C, respectively (AlFataftah & Abu-Dieyeh, 2007)
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