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Abstract
This thesis includes two studies, in the first study 693 complete lactation records of 693 Holstein cows were collected from a commercial farm (Dina Farm) during years 2011 and 2012. The aim of the first study was to evaluate some productive and reproductive traits of Holstein cows raised under two different housing systems. The first housing system (FHS) was characterized by the presence of six units of cooling operated manually, with shed height of 4.5 m and 18% shaded area. The second housing system (SHS) was characterized by the presence of 16 automatic cooling units, with a shed height of 8 m and 38% shaded area. Data on 305 days milk yield (305-dMY), daily milk yield (DMY), days open (DO) and number of services per conception (NSPC) were collected and analysed using XLSTAT. The overall means of 305-dMY, DMY, DO and NSPC were 8550±330 kg, 26.9±1.04 kg, 147±8.8 days and 3.5±0.25 services, respectively. Cows housed under the SHS produced 11% higher 305- dMY (8980 kg vs. 8120 kg) (P < 0.05), 11% higher DMY, (28.3 kg vs. 25.5 kg) (P < 0.05) and non-significant shorter DO than those of FHS (138 days vs. 156 days). Cows maintained under the SHS had lower (P < 0.05) NSPC than those maintained under the FHS by 26% (3.1 vs. 3.9 services). These results could be attributed mainly to the more comfortable microclimate conditions in the SHS, mediated by greater shaded area, roof height and effective cooling system