Morphological and steroidogenic assessment of ovarian activity during lactation in the spotted hyaena (Crocuta crocuta)

Histological evidence suggests that the spotted hyaena ( Crocuta crocuta ) is polyoestrous, and that corpora lutea are persistent and are not visible after one birth interval. Multiple generations of corpora lutea therefore represent recurring 'infertile' oestrous cycles. Plasma oestradiol-17β and progesterone concentrations fluctuate concurrently, with the highest concentrations occurring during pregnancy. The reduced mean oestradiol-17β concentrations observed during lactation suggest reduced ovarian steroid secretion during this reproductive phase. However, signs of follicular activity in some lactating females indicate that endocrine activity may still occur during lactation. The presence of multiple 'infertile' cycles and some degree of follicular development during lactation explains the ability of this species to fall pregnant soon after the loss of a litter, and provides a mechanism for overcoming the low recruitment rate so characteristic of this species.