الفهرس 
Material and methodsOnly 14 pages are availabe for public view
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Abstract
Animals of the commercial Holstein Friesian herd of the study recorded better performances than those of the cited literature for age at first calving , longevity traits ( age at last calving , length of productive life , length of herd life and number of lactations completed before disposal ) in addition to lifetime milk production traits ( lifetime 305-day milk yield , lifetime total milk yield , lifetime days in milk and milk yield per day of productive life ) . This would refer to the preferential husbandry in the commercial herd of the study
Percentages of variation in longevity and major lifetime milk production traits generally make it possible to improve these traits
through phenotypic selection .
Year of birth, was found to have an important significant ( p < 0.05 p < 0.01 or p < 0.001) effect on all longevity and most lifetime milk
production traits .
Results of the effect of the interaction between year of birth and season of birth constituted an important significant ( p < 0.05 , p < 0.01 or p < 0.001 ) source of variation in longevity and lifetime milk production traits indicating that the effect of season of birth on these traits differs from one year of birth to another .
Expected genetic improvement in longevity traits through direct selection would probably be ineffective ( little or nill ) .
Results of this work would indicate that direct selection for early age at first calving and high first lactation milk yield would lead to increase lifetime milk yield , number of complete lactations given and prolong longevity of cows .The strong genetic correlation coefficients among longevity and lifetime milk production traits in all possible combinations would suggest that any of these traits adequately measures the performance of the cow for any of these traits and the improvement in one of them would result in an improvement in any of the others .