الفهرس 
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Abstract
The present study was carried out at Sakha Animal Production Research Station, belonging to the Animal Production Research Institute, during the period from November 2004 to March 2006. A total of 20 Friesian heifers was used in this study having live body weight of 193 kg and 810 months of age. Animals were divided into two similar groups, the 1st group (control) was fed on concentrate feed mixture (CFM) and heifers were fed on 1% formaldehydetreated CFM in the 2nd group. The aim this study was undertaken to investigate the effect of feeding protected protein diets during prepubertal ages on growth performance, rumen parameters, haematological and biochemical, LBW and age at puberty, and reproductive performance. The results indicated the beneficial effect of feeding Friesian calves on PP diet on increasing their LBW, ADG, feed efficiency and protein efficiency as compared to the control heifers. Values of ruminal pH increased (P<0.05) while VFA and NH3N in rumen liquor decreased (P<0.05) in PP than C group. In whole blood, white and red blood cells increased in PP than C group. Concentration of hemoglobin and PCV % increased (P<0.05) in PP than C group. Concentration of total protein, albumin, lipids and cholesterol and in blood serum increased (P<0.05) in PP than C group. ureaN and creatinine concentrations were the lowest in PP than in control. Concentration glucose and cholesterol did not differ. Activity of transaminases did not differ. Effect of dietary PP of LBW on heifers at puberty, at 1st service and conception were not significant. However, age on heifers at 1st service and conception were signifivantly (P<0.01)lower in PP group than the control group. The results revealed nearly similarity in the ovarian activity of heifers Effect of dietary treatment was significant (P<0.05) on age of heifers fed PP at Pg peak prior to puberty than the control group. However, the differences in average Pg concentration, Pg peak and interval to peak were not significant, although there was a tendency of the lower Pg concentration, higher Pg peak and shorter interval to Pg peak in treated than the control group. Average Pg concentration at puberty was significantly (P<0.05) affected by the dietary treatment However, average Pg concentration at conception and early pregnancy was not affected significantly by dietary treatment. Results revealed that number of services per conception and service period significantly lower in treatment group than the control group.