Abstract
ABSTRACT Heat tolerance in poultry production was obtained attention due to the need for genetic lines that can withstand climate changes. This study aimed at investigating heat tolerance in commercial and native broiler genetics, as well as the physiological and growth performance responses of HSP70 genotypes submitted to heat stress. In Experiment I, heterophil:lymphocyte (H:L) ratio, as an indicator of heat tolerance, was compared between commercial broilers (n = 100) and Thai native chickens (n = 100). Growing chickens (with similar initial weight) of each genetic strain were randomly divided into two groups: 1) thermoneutral environment (26 oC ± 2 oC) and 2) heat stress (36 oC ± 2 oC). The results showed that native chickens originating from a tropical environment presented lower H:L ratio and mortality rate compared with commercial broilers. In Experiment II, HSP70 genotypes were compared. PCR-RFLP was applied to identify the genotypes (C1C1, n = 38; C1C2, n = 38; and C2C2, n = 28). Ten-week-old chickens of each genotype were evaluated in the same environments described in Experiment I. Heat-stress indicators - respiratory rate (RR), cloacal temperature (CT), packed cell volume (PCV), and average daily gain (ADG) - were measured for three weeks. The significant difference in PCV indicated that C2C2 chickens were less tolerant to heat stress compared to other genotypes. The RR, CT, and ADG were not significantly different among all genotypes. Since the C2C2 genotype was shown to be sensitive to heat stress, C1C1 and C1C2 could be used as markers for heat-tolerant genetic strains of Thai indigenous chickens and hybrid commercial lines.
Highlights
Heat stress has negative effects on the productivity and welfare of poultry
Several recent reports show that heat stress adversely affects feed intake (Cooper & Washburn, 1998), water intake (Bruno et al, 2011), growth performance (Altan et al, 2000; Abu-Dieyeh, 2006), blood variables (Altan et al, 2000; Aengwanich, 2007), electrolytes (Borges et al, 2004), and the immune system (Zulkifli et al, 2000b; Mashaly et al, 2004; Tirawattanawanich et al, 2011), increasing mortality (AlFataftah et al, 2007).The optimal temperature range for commercial broilers is about 21-26 oC (Ewing et al, 1999), and a temperature of 32 oC causes heat stress (Daghir, 1995)
The average daily gain (ADG) of native chickens was not affected by heat stress, indicating the heat tolerance of this native breed
Summary
Heat stress has negative effects on the productivity and welfare of poultry. Heat stress is responsible for the morbidity and mortality of one million broilers per month (Guerreiro et al, 2004). The genetic selection for heat-tolerant broilers is a challenge in global poultry production. Very few exotic breeds, have adequate heat tolerance (Duangduen et al, 2007). The introgression of genes from heat-tolerant lines into grand parental stock is an effective strategy applied to accelerate the genetic progress of commercial lines that can tolerate heat stress. The genes affected the appearance and some performance parameters of the chickens
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