الفهرس 
Effect of month or season of calvingOnly 14 pages are availabe for public view
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Abstract
Data used in this study were obtained fiom milk records of Friesian cows kept at Dalla farm which it far fiom Cairo City by 100 Krn , during the period from 1987 to 1992. A total of 241 5 lactation records of cows producing for at least 100 days were used. Number of cows, sires and number of daughtres per sire were 706,308 and 7.7, respectively. The purposes of this study were : 1) estimate non - genetic factors affecting cumulative milk yield (CMY) and 3 05 day milk yield (3 05 d MY) such as month and year of calving and parity, 2) estimate phenotypic and genetic parameters for the same traits studied, 3) estimate sire transmitting ability for cumulative milk yield and 305 day milk yield and 4) product moment correlations between sire transmitting ability for different traits were also examined. The results obtained from the analysis of the data could be summarized as follows. 1- Least squares means of 30 dMY: 60 dMY, 90 dMY, 120 dMY, 150 dMY, 180 d MY, 210 d MY, 240 d MY, 270 d MY and 305 d MY were 322 ,969,1609, 2219,2783,3301,3777,4200, 4537 and 5028 kg, respectively. 2 - Month of calving had a significant effect on cummulative monthly milk yield and 305 day milk yield except for 30 d MY . In addition, Spring calvers had the highest CMY and 305 d MY. 3 - Year of calving had a significant effect on different traits studied. 4 - Parity had a significant effect on each of CMY and 305 d MY . The present results indicate that CMY and 305 d MY reached maximum level in the fourth lactation.