THE ENDOCRINOLOGY OF GESTATION FAILURE IN FOXES (VULPES-VULPES)

The endocrine basis of reproductive failure in red fox vixens was exam ined over two breeding seasons in a total of 11 animals. Weekly blood samples were assayed for progesterone, prolactin, LH and cortisol. Vag inal smears taken every 2 days over the oestrous period indicated that all vixens had mated. Vixens that successfully gave birth to a litter of cubs demonstrated significantly higher plasma progesterone and pro lactin concentrations but significantly lower cortisol concentrations than did females that had ovulated, but then failed to whelp. There we re no significant differences in plasma LH concentrations. These data suggest that reproductive losses could result from lowered plasma prog esterone concentrations, possibly resulting from inadequate luteotroph ic support by prolactin. A stress-induced mechanism of reproductive fa ilure is implicated and is discussed in relation to social suppression of reproduction.