الفهرس 
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Abstract
The experimental work of this study was carried out during the period from 2014 to 2015 in the Poultry Research Farm, Department of Poultry Production, Faculty of Agriculture, Menoufia University, Shibin El- Kom, Egypt. Data collected on Norfa chickens were used to investigate the possibility of using immunity level of chicks and its relation with heat shock protein 70 concentrations to predict the ability of chicken (older age) to tolerate the future exposure to heat or cold stress. Birds divided into 3 groups according to its immunity level (High – Low – Control). The groups were subdivided into subgroups (heat (37 ˚C / 57% humidity) and cold (10 ˚C / 76% humidity) which subsequently, exposed acute and chronic heat treatment. The results of the present study could be summarized as follows:
1. Physiological traits:
1.1. Heat shock protein70 (Hsp 70):
Acute heat stress: Birds with high immunity levels which exposed to cold stress for 6 hours had the highest values of Hsp70 (0.056±0.0045). There were no significant differences with the other levels except for the birds with high immunity levels which exposed to high temperature stress for 3 hours. There were no significant differences among all exposure periods for the birds of low immunity level.
Chronic heat stress: Birds with high immunity levels which exposed to high temperature stress for 6 days had the highest values of Hsp70 (0.086±0.0031) which had significant differences (P≤0.05) compared with the other groups. Regarding the birds of the low immunity levels which exposed to cold temperature stress for 6 days had high value of Hsp70 more than the birds which exposed to the same stress for only 3 days.
1.2. Immunological Response(I.R):
Acute heat stress: There were significant differences (P≤0.05) between the birds of high immunity which exposed to cold and high temperature stress for 3 hours (16.05±1.64) (15.75±1.58), respectively and the others which exposed to 12 hours (10.51±1.71) (10.44±1.64), respectively for I.R after exposure to heat stress. There were no significant differences for the effect of birds with high immunity levels which exposed to low and high temperature stress for all its periods of exposure on I.R before exposure to heat stress. There were no significant differences between its periods of exposure for the birds of low immunity levels.
Chronic heat stress: Birds with high immunity level which exposed to high temperature and cold stress had significant differences (P≤0.05) between 3 and 6 days on I.R before and after exposure to heat stress. But, there were no significant deference between 3 and 6 days group under cold stress conditions for high immunity group effects on I.R after exposure to heat stress. The same trend was found which birds with low immunity under high temperature stress. The differences between 3 days group under the low temperature stress conditions for low immunity group were significant differences (P≤0.05) for I.R before and after exposure to heat stress. But, there were no significant differences on birds with high immunity level which exposed to low temperature stress for all its periods of exposure on I.R before and after exposure to heat stress were found.1.3. Blood characteristics:
1.3.1. Red blood cells (RBCs), Hemoglobin value (Hb), packet cell volume (PCV), Mean cell hemoglobin (MCH) and Mean cell hemoglobin concentration (MCHC).
Acute heat stress: There were significant differences (P≤0.05) between the birds of high immunity which exposed to cold stress for 6 hours and the others for 12 hours for MCH and MCHC traits. While for RBCs, there were significant differences (P≤0.05) between birds of high immunity which exposed to cold stress for 3 hours and the others which exposed to cold stress for 6 hours. There were significant differences between the birds of high immunity which exposed to heat stress for 3 hours and the others which exposed to heat stress for 12 hours for RBCs, MCH and MCHC traits.
There were significant differences between (P≤0.05) the birds of low immunity which exposed to heat stress for 3 hours and the others which exposed to heat stress for 12 hours for Hb, MCH and MCHC traits.
Chronic heat stress: Generally the levels of RBCs, Hb, PCV, MCH and MCHC increased as the periods of exposure increased from 3 to 6 days in the low and high temperature stress in both high and low immunity groups. The differences between 3 days groups under the high temperature stress conditions for high immunity group and the control group were significant for the same parameters. The higher values of interaction were found in high immunity despite of the levels of heat stress and exposure periods, while the lower values were found mostly in low immunity despite of the levels of heat stress and its exposure periods on RBCs, Hb, PCV, MCH and MCHC parameters.
1.3.2. White blood cells(WBCs), Heutrophil (H), Lymphocyte(L), heterophils : lymphocytes ratio (H/L ratio), Monocyte (M), Esinophil (E) and Basophil (B).
Acute heat stress: Birds with high immunity levels which exposed to cold and high temperature stress for 3 hours had the highest values of parameter. There were no significant differences between the interaction of high temperature stress and its exposure periods group with high and low immunity effects on WBCs, L, H/L ratio, M, E and B.
Chronic heat stress: The differences between 3 days group under the cold stress conditions for high immunity group and the control group were significant differences (P≤0.05) on WBCs, L and H/L Ratio. The higher values of interaction were found in high immunity despite of the levels of heat stress and its exposure periods, while the lower values were found mostly in low immunity despite of the levels of heat stress and its exposure periods on WBCs, H, L, H/L Ratio, M, E and B parameters.
1.3.3. Triiodothyronine hormone (T3), Thyroxin hormone (T4), T3/T4 Ratio and Adrenocorticotropic Hormone (ACTH).
Acute heat stress: The differences among 3, 6 and 12 hours group under the high temperature stress conditions for high and low immunity groups were not significant differences on T4 and ACTH. However, the levels of T3 and T3/T4 ratio were significant different (P≤0.05) from 6 hours in the cold and high temperature heat stress in both high and low immunity groups. Also, there were significant differences (P≤0.05) for the birds with high and low immunity levels which exposed to low and high temperature stress for 12 hours on T4 and ACTH.
Chronic heat stress: The differences between the birds with high and low immunity groups of heat stress and its exposure periods for T3 and ACTH were not significant. Also, there was no significant difference between the interaction effect of high immunity, chronic heat stress and its periods of exposure for T3/T4 ratio. However, the birds of the high immunity levels which exposed to cold and high temperature stress for 3 days had significant differences (P≤0.05).
1.3.4. Liver enzymes, Aspartate amino transferase (AST) and Alanine transaminase (ALT).
Acute heat stress: There were significant differences (P≤0.05) in the levels of AST between the birds with high immunity that exposed to cold stress for 6 hours (20.0±1.37) and the other group which exposed to high temperature stress for 3 and 12 hours.
There were significant differences (P≤0.05) between the birds with low immunity which exposed to 12 hours and the other group under cold and high temperature stress on AST and ALT levels.
Chronic heat stress: Birds with high immunity levels which exposed to high temperature and cold stress for 3 and 6 days had significant differences (P≤0.05) compared with the other groups on AST. Regarding the birds of the low immunity levels which exposed to cold temperature stress for 3 and 6 days had high value of AST levels. Birds of high and low immunity levels, there were no significant differences among all levels were found on ALT enzyme levels.
1.4. Rectal temperature (R.T).
Acute heat stress: Between R.T before and after exposure were significant differences (P≤0.05) from 6 to 12 hours in the cold and high temperature stress between high and low immunity groups.
Chronic heat stress: There were significant differences (P≤0.05) between the birds of high immunity which exposed to cold stress for 3 days and the others for 6 days on R.T before and after exposure.
There were significant differences (P≤0.05) between R.T before and after exposure to cold stress for 3 days and the others which exposed to cold stress for 6 days for birds of low immunity which exposed. Also, there were significant differences (P≤0.05) between the birds of low immunity which exposed to cold stress for 3 and 6 days on R.T before exposure.
1.5. Respiratory rate (R.R).
Acute heat stress: There were significant differences (P≤0.05) for the birds with high immunity levels which exposed to high temperature stress for 3 and 6 hours on R.R before exposure and after exposure to heat stress. The birds of low immunity levels there were no significant differences among all levels were found on R.R before exposure to heat stress.
Chronic heat stress: The differences between R.R before and after exposure to 3 and 6 days group under the heat stress conditions with different immunity levels group were significant (P≤0.05). But, the birds of the high immunity levels which exposed to high temperature stress for 3 and 6 days had no significant differences between R.R before and after exposure. Also, the differences between the 3 and 6 days groups were not significant for all treatment groups on R.R before exposure
1.6. Mortality rate (M.R).
Acute heat stress: There were significant differences (P≤0.05) between the birds of high immunity which exposed to cold and heat stress for 3 hours and the others which exposed to heat stress for 6 and 12 hours for mortality rate.
Chronic heat stress: Generally the mortality rate increased as the periods of exposure increased from 3 to 6 days in the cold and high temperature stress in both high and low immunity groups. The differences between heat stress for 3 and 6 days group under the heat stress conditions with different immunity levels group were significant (P≤0.05) on mortality rate.
2. Productive traits:
2.1. Body Weight
Acute heat stress: The differences among 3, 6 and 12 hours group under the high temperature stress conditions for high and low immunity groups were significant differences (P≤0.05) on body weight at 20 WK of age.
There were significant differences (P≤0.05) from 6 to 12 hours in the cold and high temperature stress in both high and low immunity groups for 36 WK of age. Also, the same result under the high and low temperature stress conditions for high and low immunity groups were found on body weight at 16 WK of age.
Chronic heat stress: The differences between 3 and 6 days groups under the high temperature stress conditions for high immunity group were significant differences on body weight at 20 WK of age. Also, the same
result under the high temperature stress conditions for low immunity group was found on body weight at 20 and 36 WK of age. However, there were no significant differences from 3 to 6 days in the cold and high temperature heat stress in both high and low immunity groups on body weight at 16 WK of age.
2.2. Growth rate
Acute heat stress: There were no significant differences for the interaction between high temperature stress and its exposure periods group with high and low immunity effects on different growth rates.
Chronic heat stress: There were no significant differences among different growth rates of the interaction between heat stress and its exposure periods group with high and low immunity effects.
2.3. Egg production:
Acute heat stress: There were no significant differences between the birds of high immunity or low immunity which exposed to cold stress and the others exposed to heat stress under different periods of exposure on Asm, EN90and EN42.
However, there were significant differences (P≤0.05) between the birds of high immunity which exposed to cold and heat stress for 3 hours and the others which exposed to heat stress for 12 hours on EN90, EN42 and EWm traits.
Chronic heat stress: Generally the levels of EN90, EN42 and EWm decreased as the periods of exposure increased from 3 to 6 days in the cold and high temperature stress in both high and low immunity groups. There were significant differences (P≤0.05) between the birds with high and low immunity groups of cold stress at 3 and 6 days on Asm, EN90 and EWm. Also, for Asm and EWm the differences between 6 days group under the
high temperature stress conditions for high and low immunity group were significant differences (P≤0.05). However, the differences between the 3 and 6 days groups were not significant under the cold and high temperature stress conditions for low immunity group for EN42.