Hepatic concentration of heat shock protein 70 kD (Hsp70) in broilers subjected to different thermal treatments

1. The relationship between repeated thermal treatments and hepatic synthes is of Hsp 70 was studied in broiler chickens. 2. Sixty broilers were submitted to 5 different treatments (12 birds each) from day 1 to day 42. Four groups were kept in a thermoneutral environment and subjected to 0, 1, 2 and 3 heat stress episodes at 35 degrees C for 4 h per week (TN-0, TN-1, TN-2 and TN-3, respectively). The last group (HT-35) was reared at a room temperature of 35 degrees C. 3. From 39 to 42 old, the birds experienced acute heat stress at 41 degrees C. Resistance to heat stress was evaluated by the time taken for rectal te mperature to increase by 3 degrees C above the pre-treatment value. Livers were collected (before and after heat stress) and Hsp70 was determined usin g Western Blot analysis with monoclonal anti-Hsp70 antibody. 4. Resistance to heat stress and concentration of Hsp70 were higher in thos e birds subjected to more heat stress episodes during the experimental peri od (TN-3) and HT-35. A positive correlation was observed between Hsp70 conc entration and the time taken for a 3 degrees C increase in rectal temperatu re (r=0.42; P<0.01). 5. Exposing birds to episodes of heat stress (35 degrees C) during rearing may improve their resistance to acute heat stress, but the previous thermal history did not seem to influence the hepatocyte Hsp70 content after expos ure to more severe heat stress (41 degrees C).