الفهرس 
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Abstract
This study was carried out at Mallawy Poultry Research Station, Animal Production Research Institute, Agriculture Research Center, Ministry of Agriculture during the period from 1 st of June to the end of August 1988.
Two breeds of laying hens at 10th month of age were used. One hundred sixty of each Fayoumi and Lohman Selected Leghorn (L.S.L.) were divided randomly into four treatments each of 40 chickens. Treatment 1- served as control (fed on the experimental diet and drank normal water); treatment 2- chickens fed on the experimental diet and drank water supplemented with 100 mg vit. C/L; treatments 3- chickens were fed on a diet of (95% experimental laying diet + 5 % vegetable oil) and drank normal drinking water; treatment 4- chickens were fed as in treatment 3- but were allowed to drink water supplemented with vit. C (100 mg/L).
Results obtained can be summarized as follows
1. Generally, under summer temperature L.S.L. chickens had
remarkable superiority over Fayoumi chickens in the produc-
tive characteristics except in mortality, shell thickness
and Haugh unit scores.
2. During summer months chickens received vit. C in the drink-
ing water had significantly higher body weight, feed
consumption and egg weight; and significantly lower feed
conversion and less mortality when compared by control group. While adding fat by 5 % to the laying diet improved significantly feed conversion and egg number; and reduced feed intake and increased mortality rate.
3. Supplementation of vit. C in the drinking water during summer improved significantly the parameters studied (Shell thickness, yolk index and Haugh unit) of egg quality. Furthermore addition of 5% fat significantly declined these parameters.
4. Chickens received vit. C had lower rectal temperature and
respiration rate than control in both measuring times.
While added fat to the laying diet took an opposite direc-
tion.
5. Plasma total protein, albumen and globulin were significan-
tly increased when compared with control group for the
chickens which received vit. C in their drinking water or
those received 5 °o fat in their diet.
6. Addition of 5 % fat to the laying diet increased significantly the plasma total lipids and plasma cholesterol in compar.sion with the other groups. While chickens received vit. C had higher values than control group.
7. Level of calcium and phosphorus in plusma were increased in
groups supplemented by 5 o fat in their diet than control.
However chicknes got vit. C in their drinking water had
higher levels of plusma calcium and phosphorus than control from those results, it can be concluded that supplementa-
tion of laying hens by either vit. C or 5 % vegetable oil was in behalf of reactions in both breeds (Fayouni and L.S.L.) hereat improves the productive characteristics.