الفهرس 
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Abstract
The present study was conducted a total number of 204 Holstein cows aged 3-8 years were used in this study, 119 cows used in the preventive program while 85 cows used in the treatment programs.
The study classified into two section, the first was prophylactic strategy were included 85 animals were divided into two groups according to the lactation season, in first experiment all animals treated with GnRH (Buserelin or Gonadorelin) at day 14 and 21 postpartum as a prophylactic treatment for cystic ovarian disease.
The second section was the treatment strategy, which included 119 cystic animals which divided in three treatment programs (GGP, GP and GPG) using two GnRH analogue (Buserelin or Gonadorelin) to detect the best treatment strategy for COD.
Diagnosis done by rectal palpation applying the criteria of cystic ovaries and clinical signs. We depended on absence of the cyst in judgment of each treatment programs.
1. Effect of using GnRH (Buserelin and Gonadorelin) in post partum period to avoid incidence of COD.
In first experiment there was no significant difference by using two dose of GnRH at day 14th and 21 post partum in cows at first season of lactation (37.5% - 33% and 37.5%), (Buserelin group, Gonadorelin group and control group respectively), while the percentage of incidence decreased in cows more than one season by using Buserelin by 8%, and decreased by 11% by using Gonadorelin than the control group (38.7% - 35.7% and46.6%), (Buserelin group, Gonadorelin group, control group respectively), but also with no significance difference.
2. Effect of using GnRH (Buserelin and Gonadorelin) in post partum period on fertility parameters.
Also in the first experiment we refer to the effect of using GnRH in postpartum on the fertility parameters, and we found that there was no significance difference or enhancement to fertility parameters more than cows not treated with GnRH, (days to first estrous, first service conception rate, days open and number of services per conception).
3. Percentage of incidence of cystic ovaries in high yielding dairy cows.
By collecting data and results in first experiment we found that the percentage of cystic ovaries in the herd was 42%, the high milk yield has a role in this percentage especially many of cows in this trial in its peak may reach more than 50 kg milk daily, most of cows get more than 9 tons in season.
For example we excluded a cow had a continuous and repeat cystic ovary from this study because its daily milk yield was 65 kg, it hade a cyst for 5 months and take more than 10 dose of GnRH with no response.
4. Effect of age in COD incidence.
We found a noticeable relation between the age of animals and incidence of COD, incidence of COD in cows in first season of lactation was 37.5%, while in cows more than one season was 46.6%.
5. Comparing three treatment programs (GGP, GP and GPG) and two GnRH analogue (Buserelin and Gonadorelin) in treatment of cystic ovaries.
In second study we use two types of GnRH Buserelin and Gonadorelin and three programs for treatment of COD. Using of Buserelin by two different ways GGP and GPG, the percentage of treated animals were 70.24% and 68.4% respectively, while using Gonadorelin by GP achieved 93.1% cure rate with significance difference with the previous two programs with Buserelin.
Briefly stated, the main results of the studies described in this thesis are:
• Using GnRH in post partum period has no significance difference compared to non treated animals on preventing COD incidence.
• Using GnRH in post partum period has no significance difference compared to non treated animals on fertility parameters.
• Percentage of incidence of cystic ovaries in high yielding cows may reach 42%.
• Cows after the first season of milking is more acceptable to COD than in first season by about 9%.
• Using two dose of GnRH (Buserelin acetate) in treatment of COD about 70% of animals responded to the treatment by exhibiting normal signs of estrous and disappearance of the cyst.
• Using one dose of GnRH (gonadorelin diacetate tytrahydrate) in treatment of COD, 93.1% of animals responded to the treatment by exhibiting normal signs of estrous and disappearance of the cyst.
• Using Gonadorelin in treatment of COD is more effective by 23% than Buserelin.
• There was significance difference between using Buserelin and Gonadorelin in treatment of COD.
Finally we recommended that the prophylactic strategies using Buserelin or Gonadorelin to prevent COD in Holstein cows give slightly improvement in the predicting incidence of COD. Also using Gonadorelin in COD treatment is more effective than Buserelin.