الفهرس 
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Abstract
The present study was carried at the Experimental and Research Unit of Toukh Tanbesha for Animal production, which belonging to Faculty of Agriculture, Menoufia University, Egypt. The farm locates in Toukh Tanbesha Village in the Middle Nile Delta, Egypt. Data were collected from the records of Friesian herd during the period from the 1997 to 2008 which include 1948 normal first lactation records.
The objective of the present study was to investigate the genetic relationships among some dairy traits in Friesian cattle in Egypt. Milk yield traits (305 day milk yield, total milk yield, lactation period, Life time production and longevity) and age at first calving were studied. Also relationships among 305 day milk yield and part lactation (single month milk yield in third, fifth and sixth month) and (cumulative milk yield in 90, 150 and 180 day milk yield) were investigated.
These relationships were investigated to depend on the first traits in selection procedures to improve cows’ performance in the later traits.
Fixed effects of year of calving, season of calving were studied as well as random effect of Sire and Dam.
Results can be summarized as follows:
1- Mean of 305 day milk yield was estimated as 3633.66 kg ± 1672.47 kg and coefficient of variation was nearly 46%.
2- Mean of total milk yield was 4323.44 kg ± 2114.11kg and coefficient of variation was nearly to 49%.
3- Mean of lactation period which was 297.13 day ± 110.86 day and the coefficient of variation of 37%.
Summary and Conclusion
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4- Mean of life time production which was about 12306.85 kg ± 4957.37 kg and coefficient of variation was nearly to 40%.
5- Mean of longevity was 949.32 day ± 317.65 day and coefficient of variation was nearly to 33%.
6- Mean of milk yield in the third month, was 520.77 kg ± 221.21 kg and coefficient of variation was 42.48%.
7- Mean of milk yield in fifth month was 399.84kg ± 223.94kg and coefficient of variation was 56.01%.
8- Mean of milk production in sixth month was 402.33kg ± 205.64kg and coefficient of variation was 51.11%, respectively.
9- Mean of cumulative milk yield in 90 day, standard deviation and coefficients of variation were 1475.49 kg ± 527.49 kg and coefficient of variation was 35.75%.
10- Mean of cumulative milk yield in 150 day was 2337.08 kg ± 860.78 kg and coefficient of variation was 36.83 %.
11- Mean of cumulative milk yield in 180 day was 2931.45 kg ± 963.42 kg and coefficient of variation was 32.86%.
12- Mean of age at first calving was 27.14 month ± 2.04 month and coefficient of variations of 8%.
13- Sire of the cow was a significant source of variation in milk production traits of the study (305-day milk yield, total milk yield, length of lactation period, life time production (p>0.01) and longevity (p>0.05)), where Dam had not significant effect on all studied traits.
14- Heritability estimates of 305-day milk yield, total milk yield, lactation period, life time production, longevity and age at first calving were found to be 0.33, 0.27, , 0.12, 0.24, 0.01 and 0.04, respectively.