Concentrations of progesterone, prolactin and relaxin in the luteal phase and pregnancy in normal and short-cycling German Shepherd dogs

Aims: In German Shepherd dog breeding bitches a relatively high incidence of short oestrous cycles of 3 to 4 months combined with a history of sub- or infertility is observed. The aim of the present study was to discover possible endocrine disorders by analysing hormones with relevance for luteal function and pregnancy in bitches with normal and short oestrous cycles. Material and methods: 22 non pregnant and 19 pregnant German Shepherd dog bitches were grouped according to normal (control) and short interoestrus intervals (duration > 6 months and < 5 months, respectively). Concentrations of progesterone, prolactin and relaxin were measured during luteal phase and pregnancy. Results: The non-pregnant bitches with shortened cycle had significantly lower progesterone values than the normocyclic controls. In the pregnant dogs with short oestrous cycle luteal function could not be evaluated due to progesterone supplementation. In this group significantly lower concentrations of prolactin and relaxin were found from day 20 to 60 compared to the pregnant controls. Furthermore the incidence of embryonic/fetal losses was increased. Conclusion: The results indicate decreased luteal function in short cyclic bitches both in the autonomous and prolactin dependent luteal phase probably due to pituitary failure. Clinical relevance: The relatively high incidence of short oestrous cycles within a breed points to a genetic background. Therefore medical care in such bitches should concentrate on the diagnostic of luteal function and selection of bitches with intact ovaries for breeding.