[Luteal insufficicency in the bitch - symptoms, diagnosis, consequences and therapy. A review of the literature].

Insufficient progesterone synthesis, so called hypoluteoidism or luteal insufficiency, is one of the possible reasons for infertility in the bitch. Confirming this diagnosis may be difficult if the dynamic changes of progesterone during the reproductive cycle are not taken into account. The bitch ovulates at progesterone concentrations of about 5-10ng/ml (15.7-31.4 nmol/L). The concentrations increase to >25ng/mL (78.5 nmol/L) within 3-4 weeks and then subsequently decrease after a plateau of 7-14 days. In the pregnant bitch, progesterone rapidly drops to <2ng/ml (6.3 nmol/L) approximately 24-48 hours before parturition induced by PGF2α secretion. Luteal insufficiency, characterized as an early decrease of progesterone secretion, is most commonly observed between days 20 and 35 of pregnancy. Progesterone concentrations of approximately 2ng/ml (6.3nmol/L) are thought to be necessary for maintaining pregnancy. Lower concentrations result in resorption and abortion, respectively. In bitches suspected to have luteal insufficiency, weekly progesterone determinations using quantitative tests should be performed from 5-7 days after mating or at least from the date of early pregnancy diagnosis. The frequency has to be increased in the case of progesterone concentrations below 10ng/ml (31.4 nmol/L). Progesterone administration is indicated in the case of viable foetuses and progesterone concentrations <5 ng/ml (15.7 nmol/L) before day 58/60 of pregnancy or after the detection of a rapid progesterone decline of about 10-15ng/ml (31.4-47.1 nmol/L) between days 20 and 35 with viable foetuses in the sonographic examination. Either natural or synthetic progestins can be used. However, synthetic progestins have a greater risk potential for side effects (masculinisation of female puppies and cryptorchidism in male puppies), especially when administered between days 20 and 35 of pregnancy. Administration of natural progesterone should be stopped 2-3 days before expected parturition otherwise it would result in a prolonged duration of pregnancy with dystocia and stillbirth.