الفهرس 
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Abstract
This study was carried out in the farm of Animal production department, Faculty of Agriculture, Minia University during the period of March to September 2011 (7 months) and was continued till calving. The aim of this study was to investigate the effect of using L-tyrosine and hormonal treatments protocol (GnRH-PGF2a-GnRH, Ovsynch) on productive and reproductive performance of high-grade Friesian lactating cows under Minia governorate conditions. Also, the effect of different reproductive stages on some blood components was studied. Fifteen highhgrade Friesian lactating cows in the fourth and fifth lactation seasons. The beginning of the experiment was after 60 days of calving. The experimental animals were randomly divided into three equal groups (5/each) according to their body weight, lactation season and milk production as follow: (control), L-tyrosine oral administration (100 mg/kg body weight), and Hormonal treatment (GnRH---PGF2a---GnRH) Lm injection. One ration was formulated to cover the requirements for maintenance and production. The experimental ration was consisted of concentrate mixture and wheat straw that represented 70% and 30%, respectively of the requirement. The experimental ration contained 15.85% crude protein and 67.61% TDN. It was offered in two equal portion at 8.00 am and 6.00 pm.
Data collected including:-
1- Reproductive performance:
Days open, calving interval, gestation period, number of services per conception, weight of borned calves and conception rate.