Thermotolerance Acquisition in Native Chicken and its Crosses by Early Thermal Conditioning Through Expression of Heat Shock

Abstract:

The present experiment was conducted to study the effect of thermal conditioning on liver HSPs mRNA expression and serum T3 levels in native chicken Aseel (ASL), Naked Neck (NN), and it’s cross variety Aseel x Nandanam chicken-4 (ARW) and Naked neck x Nandanam broiler-3 (NNB3) under heat stress. Chicks from four varieties (ASL, ARW, NN, NNB3) were divided into control (C) and heat-exposed (H) groups. The control chicks (C) were reared in at ambient temperature (28±1°C). H group chicks were heat stressed at 39±1º C for 2 hours daily during 0-2 weeks and 5-6 weeks of age. In 12th week, the control group (C) was divided into two groups i.e., unexposed control (C) and control exposed (CE). Birds from H (HE) group and the CE group were thermal challenged 39±1°C for 4 hours daily on the 12th week. On 14th, 42nd, and 84th day, serum was collected and processed for Triiodothyronine (T3) by Radioimmuno assay kit. The Cloacal temperature and T3 concentration were significantly (p<0.01) high and low in the H group, irrespective of varieties at 14th and 42nd d. On the 84th d birds from each group were sacrificed and liver samples were collected for further processing. On 84th day the relative mRNA expression (fold change) of all four HSP genes (HSP 20, 60, 70, and 90) were significantly (P<0.01) high in HE and CE groups in all four varieties. CE (suddenly exposed) group birds, not exposed to high temperature during early age had significantly (P<0.01) high mRNA expression, while pre-conditioned birds (HE) had significantly (P<0.05) low gene expression. From the present study, it can be concluded that the thermal conditioning of chicks during early age had a positive effect and improves the thermo tolerance in the later part as revealed by the low expression of the HSPs gene, temperature, and improved T3 levels as stress indicators in native chickens and its cross varieties.