| Abstract |
Two experiments were conducted to study the effect of heat stress
on the physiological, hematological and immunological responses of two strains or turkcy (Nicolas and Bronze) .
First cxperiment : Two strains of turkey 12 wk old were subjected to long term heat stress at 32°C and short term heat stress at 45°C. Body
temperature (Tb), surface temperature (Ts) , respiration rate (RR), feed intake (FI) , heterophil to lymphocytes (H/L) ratio, hematocrit value
(Ht) , plasma total protein (PTP), and plasma content of heat shock
protein (Hsp)70 KDa were ili estigated. A total of 60 birds of each
strain was divided info 3 groups, 20 birds cach ; 10 of each sex. First
group was exposcd to acute heat stress at 45°C for 60 min , the second group was exposed to relatively longer heat stress at 32°C for 6 hours,
and the untreated group was kept at the normal ambient temperature of about 20°C. The relative humidities were 40 , 50 and 50 % for the first
, second and control groups, respectively. Results shows that heat stress at 45°C and at 32 °c decreased feed intake in both strains,
hematocrit percentage, plasma total protein and increased body temperature, respiration rate, heterophils to lymphocytes (H/L) ratio
and heat shock protein (Hsp) 70 Kda .The increase in Hsp 70 Kda was
associated with thc increase in the temperature of heat treatments. These results suggest that Bronze turkey could be considered as heat
tolerant strain compared with Nicolas undcr the present condition.
Using modern biotechnological techniques such as Hsp analysis is
preferable to classical methods as a tool in Marker Assisted selection (MAS) for identifying the most tolerant strain of turkey.
Second experiment : The two above mentioned strains of turkey of the first experiment (Nicolas and Bronze) were subjected to chronic heat
stress at 40 °e for 4h /3days/3weeks from 5-8 weeks of age to study the physiological response which influenced by the effect of chronic heat
stress. Feed consumption, water consumption, weight gain (WG) , fced conversion, body temperature (Tb) , respiration rate (RR) , H/L
ratio, plasma total protein (PTP) , glucose, insulin, thyroid hormones (T3 and T4) and plasma electrolytes ( Ca , P, Na, K , Mg , Mn and Zn )
were measured. A total of 40 birds of each strain was divided into 2
groups, 20 birds each; 10 of each sex. First group was exposed to chronic heat stress at 40 °C for 4 hours, the second group was kept at
the normal ambient temperaturc of about 20 °C (control). The relative
humidities were 65 and 40 % in control and heat stressed group, respectively. Feed consumption was not affected by heat stress. Both sexes responded differently to heat stress. Chronic heat stress at 40°C
decreased body weight gain and feed intake in both strains, plasma total protein, electrolytes, hemoglobin , T3 and T4 hormones, hematocrit
percentage and increased insignificantly in body temperature, respiration rate, water consumption, heterophils to lymphocytes (H/L)
ratio, mortality rate, glucose and insulin hormone compared with unstrcssed control.
The results indicated that exposure of turkey to chronic heat stress 40°C result in acceptable adaptation and increase the thermotolerance leading to maintenance of productivity.
Keywords: turkey, heat stress, body temperature, respiration rate, water consumption, feed intake, mortality rate, T3, T4, hemoglobin, hematocrit, heterophils to lymphocytes (H/L) ratio, glucose, plasma electrolytes, plasma total protein and heat-shock protein.
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