The present study aimed to investigate the effects of heat shock programs during the growth period without or with chromium picolinate (CrPic) on productive and physiological performance, blood biochemical traits as well as, immune response, heat shock proteins of Mandarah laying hens during first 90 days of egg production (EP) reared under Egyptian summer condition. Seventy hundred-one day old of unsexes Mandarah chicks were randomly divided into seven equal groups (100 chicks each). The 1st treatment was served as a control group and fed a control basal diet and reared under natural conditions. While, the chicks in 2nd, 3rd, 4th, 5 th, 6 th and 7 th treatments were exposed to early heat shock (40±1 °C for 4 hours from 12.00 to 16.00 p.m. for 3-5 consecutive days). The 2nd treatment was exposed to early heat shock at 3 days of age (HSE1). Whereas, the 3rd treatment was exposed to heat shock at 3 days of + 800 μg/ CrPic/kg diet (HSE2). The 4th treatment was exposed to heat shock at 3 days and at 8 weeks of age (HSE3). The 5th treatment was exposed to heat shock at 3 days and at 8 weeks of age + 800 μg/ CrPic /kg diet (HSE4). The 6th treatment was exposed to heat shock at 3 days and at 8 and 16 weeks of age (HSE5). The 7th treatment was exposed to heat shock at 3 days and at 8, 16, weeks of age + 800 μg/ CrPic /kg diet (HSE6).
The obtained results revealed that the egg production (EP) %, egg mass (EM) in hens and some semen characteristics in cocks exposed to heat shock were significantly (P≤0.05) improved in HSE6. Rectal temperature (RT), respiration rate (RR), heterophils % and Heterophils/ lymphocyte (H/L) ratio were significantly (P≤0.05) decreased. Birds in the treatment groups exposed to heat shock in HSE5 or HSE6 were significantly (P≤0.01) increased globulin, HSP70 of Liver, superoxide dismutase (SOD) and glutathione peroxidase (GPX). While, Triiodothyronine (T3) and total antioxidant capacity (TAOC) were significantly (P≤0.01) decreased compared to the control group.