الفهرس 
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Abstract
This experiment aimed to study the physiological changes in the digestive system , the reproductive system and egg production of laying hens due to supplementing the diet with the feed additives probiotic (beneficial bacteria which present in the gastrointestinal tract ) and methionine (an essential amino acid) .The study was conducted on 66 bovans white laying hen in a private farm in Mansoura from the beginning of the egg production period and persists for 16 weeks. The hens were randomly divided into three groups each of 22 birds. Group (1) supplemented with probiotic (BIO-TOP, SHIN-IL CHEMICAL & LIVESTOCK CO., LTD. SEOUL, KOREA) at a level of (1 gm /kg diet), group (2) supplemented with the amino acid methionine at a level of (1 gm /kg diet) while group (3) was considered as a control and given basal layer diet only (containing 16.07% protein, 2830 K.calorie /kg diet, 3.5% calcium and 0.75% phosphorous). The following results are obtained: 1. Methionine supplementation in the diet increased egg production than probiotic supplemented and the control groups by 12%. 2. There were no significant differences in egg weight between the 3 groups and also in egg albumin and egg yolk weights. 3. Result of digestive enzymes efficiency determination is that: probiotic supplementation in the diet leads to increase the digestive enzymes activity while methionine supplementation to the diet had no effect on the digestive enzyme. 4. Result of histopathological examination showed that: probiotic and methionine supplementations to the diet had no effect on intestinal mucosa morphology while they produce fatty infiltration in the liver. 5. Result of biochemical and hormonal assays showed that: probiotic supplementation leads to increase estrogen level and decrease calcium level while methionine supplementation leads to increase calcium level in plasma. It could be concluded that the diet supplied by methionine is the best diet for laying hen as methionine produce an increase in the egg production but we have to decrease methionine level in the diet after reach the peak of egg production to avoid fatty infiltration in the liver.