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Labib F., E. A. El Azab, F. A. Soliman: Hormonal Changes During Formation and Involution of Corpus Luteum in Rabbits. Acta vet. Brno, 47, 1978: 23-31. A study was made on 30 female Boscat rabbits to reveal the hormonal changes, namely, TSH, FSH, LH and L TH during the formation, maintenance and involution of the corpora lutea. Induction of ovulation was done by using gonadotrophic hormones (PMS and HCG). After HCG injection the animals were devided into 3 groups of 10 animals each. They were slaughtered after 3, 7 and 15 days from HCG injection. The results observed from this experiment are as follows: 3-day old corpus luteumThe rate of synthesis and release of TSH and state of thyroid were considered in a stabilized, balanced euthyroid status. There was increased concentration of FSH in the pituitaries with a relatively low level in the blood. This indicates the inhibition of release of FSH at this stage of development of corpora lutea.The level of L TH in the pituitary was of an average value and low in the serum. 7-days old corpus luteumThe TSH content of the pituitaries was the lowest (decreased synthesis) with a mild change in its level in the blood (non-significant). The thyroids were relatively less active than in the previous group.The FSH content of the pituitaries and blood were significantly decreased (decreased synthesis and release of FSH). The LH content of the pituitaries was increased and the level in the blood was decreased (decreased release of LH).The L TH content of the pituitaries was relatively low, while that of the blood was maximal, indicating increased release of L TH. IS-day old corpus luteumThe TSH content of the pituitaries and blood were highest indicating increased synthesis and release of this hormone. The thyroid gland showed maximum activity as compared to the previous groups.The FSH content of the pituitaries was relatively low while it reached its maximum in the serum (increased rate of release of FSH). The level of LH in the pituitaries was low and that of the blood was the least. The L TH content of the pituitaries was at its maximum and it was the lowest in the blood (increased synthesis of L TH but blocked release into the blood). The results are discussed in the text. LTH, TSH, LH, FSH, pituitary, blood serum.The features of growth and maintenance of the corpus luteum, and its subsequent involution are active processes of extreme importance in regulating reproductive performance of mammals. This includes regulation of the estrous cycle, pregnancy, parturition and milk production.Any disturbance of such processes of the corpus luteum will lead to reproductive disturbances in the farm animals.

Infertility problem is a common syndrome among bitches and its causes are numerous, but the apparent most frequent cause is the mating at incorrect time. The aim of this study was to avoid the possible causes of infertility in bitches by predicting the optimal time of breeding and try to treat disorders in estrus cycles. A total number of 18 bitches of German shepherd breed were used in this study for monitoring phases of estrus cycle and predicting the optimal time of breeding. Those bitches examined by vaginal cytology, progesterone assay, measurement of vaginal PH, vaginal endoscopy and ultrasonographic examination of ovaries from proestrus to diestrus. By vaginal cytology, cornified cells first appeared on Day 4 from the beginning of proestrus, then increased till reached to 85% on Day 12 which is considered as the ovulation day. Measuring of progesterone concentration at the beginning of proestrus was very low (less than 1 ng/ml) then increased in 13 bitches only out of 18 bitches which used in this study till reach to 6.5 ± 1.37 ng/ml within ranges (4.8 to 8.3 ng/ml) on Day 12 from the beginning of proestrus. The other five bitches showed disorders in normal sequence of estrus cycle which was discovered by progesterone assay, vaginoscopy and ultrasonography of ovaries. Abnormalities in estrus cycle were recorded; two cases of anovulation and three bitches of persistent proestrus. As a trial for correcting the deviated estrus cycle, we injected hCG hormone in two anovulatory bitches for occurrence of ovulation, and also used methergine drug in cases of persistent proestrus as a trial for stoppage of continuous bloody discharge. The optimal time of breeding in 13 ovulatory bitches was within 2 to 3 days after ovulation day. Pregnancy rate after breeding by 20 days was recorded by ultrasonographic examination was 92.3 % (12/13 bitches). When applying these applications, we concluded that progesterone hormone assay was the accurate method for predicting the ovulation time and achieving higher pregnancy rate , and also can judge on estrus cycle if normal or abnormal.