الفهرس 
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Abstract
Four broiler houses in Sharkia governorate were examined to study the microclimatic condition, occurrence of airborne bacteria, their effects on broiler performance and occurrence of pathogenic bacteria in air in different seasons.
I- Microclimatic conditions in broiler houses:
1-There was an irreversible relationship between age of broilers and relative humidity, ammonia and carbon dioxide. 2-Highest temperature was recorded in summer (34.4°C±0.41), spring (27.3°C±0.35), autumn (26.3°C±0.36) and winter (22.7°C±0.82). 3-Highest relative humidity was recorded in winter (81.5% ±22.6) followed by spring (75.2%+1.64), autumn (71.5%±2.27) and summer (71.4%±1.84). 4-Highest ammonia concentration in (ppm) was recorded in winter (10.7+1.65), spring (9.3±0.83), autumn (8.7±0.99) and summer (6.4+0.64). 5-Highest carbon dioxide concentration in (cc/L) was reported in winter (3.78+0.42), followed by spring (2.92+0.22), summer (2.53+0.22) and autumn (2.23+0.3).
II- Occurrence of airborne bacteria in broiler houses:
1- There was a steady increase in the viable count of airborne bacteria throughout the fattening period of broiler. The maximum bacterial pollution was occurred in the 6th week of broiler age (306 million bcfp/m3), (184.4 million bcfp/m3), (88 million bcfp) and (72.4 million bcfp/m3) in winter, spring, autumn and summer respectively. 2-There was seasonal variation in number of airborne bacteria inside broiler houses, it was highest in winter and lowest in summer. 3-Highest total bacterial count in (million bcfp/m3 of air) was recorded in winter (169±44.77) followed by spring (110±23.6), autumn (58±11.8) and summer (44 ±11.8). 4-Highest Staphylococci count in (million bcfp/m3 of air) was recorded in winter (131±33.98), followed by spring (63±19.9), autumn (39.4±8.17) and summer (32.2±8.86). 5-Highest Enterococci count was recorded in winter (1.4±0.57x106 bcfp/m3 of air) followed by spring (654±290x103 bcfp/m3), summer (502±230x103 bcfp/m3) and autumn (61.7±24x103 bcfp/m3).
III- Occurrence of airborne bacterial pathogens in examined broiler houses air:
Staphylococcus aureus, Streptococcus faecalis, Streptococcus intermediate, Streptococcus faecium, Escherichia coli Klebsiella pneumoniae, Klebsiella oxytoca, Proteus mirabilis, Enterobacter cloacae and Citrobacter freundii could isolated form the air of broiler houses in a percentage 5.42%, 20.93%, 13.95%, 5.42%, 17.05%, 6.98%, 6.98%, 5.42%, 9.30% and 8.53%, respectively. The highest frequency of isolates was recovered in winter and lowest in summer.
IV- Effect of microclimatic conditions and airborne bacteria on broiler performance in different seasons:
1-There was an irreversible relationship between morbidity and mortality rates recorded in broiler houses and relative humidity percent, ammonia gas concentration, carbon dioxide concentration, total bacterial count and Staphylococci count and reversible relationship with ambient temperature. 2-Highest morbidity rate was recorded in winter (10.72+2%), followed by summer (8.3+1.45%), spring (7.79+1.18%) and autumn (6.7+0.98%). 3-Highest mortality rate was recorded in winter (8+1.47%) followed by summer (7+1.33%), spring (6.29+0.93%) and autumn (5.53+0.8%). 4-Highest body weight was obtained in autumn (1582.3 gm), followed by winter (1575.8 gm), spring (1571.8 gm) and summer (1365.3 gm).