الفهرس 
Effect of parity or age at calvingOnly 14 pages are availabe for public view
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Abstract
This investigation was carried out on the millt production records of Friesian cows herd raised at Saltha experimental station and belongs to the Animal Production Research Institute, Ministry of Agriculture, Egypt. The records used in this investigation were first, second, third and for all lactations records (1 170, 780, 450 and 2400 records, respectively), obtained through the period 1976 to 1990 were used to investigate the non genetic factors affecting production and reproduction traits. Also, genetic and phenotypic parameters of these traits were studied. Data were analysed using Mixed Model Least squares analysis and Maximum Liltelil~oodC omputer Program of (Harvey, 1990). The important production and reproduction traits considered in this investigation were: Total milk yield (TMY), 305-day mill< yield (305 dMY), lactation period (LP), dry period (DP), age at first calving (AFC), days open (DO) and calving interval (CI). Results obtained can be su~nniarizeda s follow: : A- Production traits: I - Overall means of uncorrected records in TMY, 305 dMY, LP and DP were 2730 Kg, 2356 Kg, 365, d and 110, d, respectively. 2-Su111i~1er-calvers recorded the highest milk yield (P<0.05) with the longest LP compared with the other seasons, summer calvers recorded non significant shostest DP. 3- The year of calving of Friesian cows had significant (P<O.Ol) effect or. TMY, 305-dMY, LP and DP. Also, as year of calving advanced, milk yield was increased, but LP and DP were decreased.