The present investigation addresses the pharmacokinetics of human chorionic gonadotropin (hCG), intramuscularly (i.m.) administered to goats. Nine pluriparous does of the Boer goat breed, 2-6 years of age and weighing 45-60 kg, were administered 500 IU hCG (2 ml Chorulon) deep into the thigh musculature 18 h after superovulatory FSH treatment. Blood samples were drawn from the jugular vein at 2 h intervals for the first 24 h, at 6 h intervals until 42 h, and at 12 h intervals until 114 h after administration. After centrifugation, plasma hCG concentrations were determined by electrochemiluminescence immunoassay. Pharmacokinetical parameters were as follows: lag time, 0.4 (S.E.M. 0.1) h; absorption rate constant, 0.34 (S.E.M. 0.002) h; absorption half-life, 2.7 (S.E.M. 0.5) h; elimination rate constant, 0.02 (S.E.M. 0.002) h; biological half-life, 39.4 (S.E.M. 5.1) h; and apparent volume of distribution, 16.9 (S.E.M. 4.3) l. The plasma hCG profile was characterized by an absorption phase of 11.6 (S.E.M. 1.8) h and an elimination phase of 70.0 (S.E.M. 9.8) h, with considerable individual variation in bioavailability and pharmacokinetical parameters. Biological half-life was negatively correlated (P!0.05) with peak concentration (rZK0.76), absorption rate constant (rZK0.78), and elimination rate constant (rZK0.87). The results indicate that after rapid absorption, hCG remains in the circulation for an extended period. This has to be taken into account when assessing the stimulatory response to hCG treatment on an ovarian level.

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A person's accomplishments are not only achieved through one person, but the many people that are there for support, motivation and encouragement. While there are countless helpful hands that deserve my appreciation, I can mention a few individuals that have been supportive in my program. First, and foremost, I would like to thank my first supervisor Prof. Dr. Wolfgang Holtz (Doktorvater), for his invaluable advice and discussions during my study. He has been able to pass some of his experiences to me and this has allowed me to expand my knowledge in semen processing, estrus synchronisation, superovulation and manipulation of embryos. I would also like to express my appreciation for Prof. Dr. Dr. M Gauly who has given me the opportunity to work within his group. I express my deepest thanks to Prof. Dr. Christoph Knorr for scientific advice in molecular biology. Thanks also goes to Prof. Dr. Soleiman Salhab for reviewing this dissertation and his precious advice during may study. It is a pleasure to thank Mr Abdoulaye Gonde and Mrs E. Stüwe for expert technical assistance in ultrasonography and hormone analysis by ELISA, respectively. I owe my truthful thanks to the Animal Assistants Mr. Jochen Köhler and his team for their assistance. I hereby thank my colleagues at the department of Animal Sciences for various support especially Mr. Shahin, Mr Ahmad Idris and Mr Azzam Al Yacoub. I sincerely thank my parents and family for their endless love and support. This dissertation was prepared with financial support from Damascus University to whom I hereby show my deepest appreciation. II Dedication To My beloved mother and adored father My wife and sons Ali, Bilal and Husam III Chapter II Superovulation of ovsynch-synchronized Boer goats induced to ovulate with GnRH or hCG.

The purpose of this study was to ascertain whether premature luteolysis can be alleviated by substituting the ovulation inducing agent hCG for GnRH. Seventy‐two hours after the end of artificial insemination (AI), pluriparous Awassi ewes were randomly assigned to one of three treatment groups of 13 ewes each. First group received 37.5 µg of the GnRH analog Lecirelin, the second 1000 I.U hCG and the third group served as a control (received 1 ml of physiological saline solution). Blood samples were collected at daily intervals after GnRH treatment and analysed for plasma oestradiol and progesterone concentrations. Ovarian follicles were monitored ultrasonically at the time of GnRH administration, 60 hr and 84 hr later. Pregnancy was diagnosed ultrasonically at Day 35 after AI. Number and size of ovarian follicles did not differ (p > .05) among treatment groups. Onset and duration of oestrus were not affected by treatment (p > .05). No significant differences (p > .05) were recorded in oestradiol and progesterone concentrations between the treatment groups during the inspection period. Premature luteolysis became evident in ewes with longer oestrous durations by Day 6.25 after AI and amounted to 7.69%, 18.18% and 23.07% in GnRH, hCG and Control groups respectively. Pregnancy rates increased to 92.31% and 81.82% in GnRH and hCG groups, compared to 76.92% in the Control group. The results indicate that GnRH was more effective in reducing premature luteolysis than hCG. Substituting hCG for GnRH as an ovulation inducing agent was of no avail.