الفهرس 
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Abstract
This study was carried out in El-Menia governorate as a representative area of Middle Egypt with the aim of studying heat stress on adapted Friesian dairy cattle during the period of January (mid-winter season, representative for cold weather), April (spring season representative for a control thermoneutral zone) and August (mid-summer, season, representative for hot weather), 2019. Ambient air temperature (T °C) and relative humidity (RH) were used to calculate the temperature-humidity index (THI).
A total of 120 pluriparous cows aged of 4-7 years in their mid-lactation and from the second to the fourth parity belonging to small herd scales in the both desert and riverine areas were randomly selected in this study.
Accordingly, these cows were classified according to area into 61 cows in riverine area and 59 cows in the desert area. They also sub-classified according to season into summer (N=23), winter (N=23) and spring (controls, N=15) for riverine areas, and in desert area the classification was summer (N=22), winter (N=22) and spring (controls, N=15).
Clinical examination and blood sampling for serum collection were done for the selected cattle at 4 PM. Clinical examination included the measurement of rectal temperature (RT), respiration rate (RR) and heart rate (PR). Quantity of milk production, Blood sera were used for the determination of the concentrations of blood serum cortisol hormone, total protein, albumin and the activity of ALT and AST in addition to the concentrations of blood serum urea, creatinine, cholesterol, triglycerides, calcium, inorganic phosphorus and magnesium.
Metriorological data at 4 PM of the studied area showed significant differences between periods regarding air temperature (°C) and relative humidity (RH). During spring and winter the THI was less than 72, however during summer it exceeded 90 and reached up to more than 96.
There were no effects of area on the levels of RT, RR or HR during moderate, cold or during the hot environment. However, summer stress increased (P<0.05) RT, RR and HR when compared with other seasons. During summer stress. Similarly, there were no effects of area on the levels of milk production However, summer stress decreased (P<0.05) milk production when compared with other seasons.
There were no effects of area on the levels of blood serum cortisol concentrations during moderate environment, cold weather or during the hot environment. However, summer stress increased (P<0.05) blood serum cortisol concentrations when compared with winter and spring seasons.
Serum total proteins and albumin increased (P<0.05) in summer stress when compared with other seasons in both areas.
There were no effects of area on the levels of blood serum ALT and AST, but summer stress increased (P<0.05) blood serum ALT and AST when compared with other seasons.
There were no effects of area on the levels of blood urea and creatinine concentrations during moderate environment, cold weather or during the hot environment. However, summer stress increased (P<0.05) blood urea and creatinine concentrations when compared with winter and spring seasons.
Blood serum cholesterol and triglycerides concentrations increased (P<0.05) summer stress when compared with other seasons in both areas.
Summer stress increased (P<0.05) blood serum calcium and inorganic phosphorus and decreased (P<0.05) blood serum magnesium concentrations when compared with other seasons.