Postpartum behavior in female mammals is essential for early parent-child contact. After calving, lambs need to ingest colostrum for related immune protection, and early mother-lamb interactions are crucial. Despite the visual and auditory signals, the olfactory signals are decisive in the orientation of the lamb towards the mammary gland. In sheep, the inguinal sinus is located bilaterally close to the mammary gland as a bag of skin (IGS) that presents a gland that secretes a strong-smelling wax.

The functions of the IGS glands of sheep have many aspects under evaluation. The objective of the present study was to evaluate the functional aspects of the sheep IGS gland and the transcription of mRNA and the protein expression of several hormonal receptors, such as the progesterone receptor (PGR), the estrogen receptor 1 (ESR1) and 2 ( ESR2) and the prolactin receptor (PRLR) present. In addition, another objective was to obtain information on the ultrastructure of the IGS and the chemical compounds produced in this gland.



All the hormonal receptors evaluated show expression in IGS during the estrous cycle (follicular / luteal phases), pregnancy and postpartum. IGS secretion is rich in triterpenoids that differ entirely from the surrounding skin. They can be essential substances for the development of an olfactory preference of newborns towards their mothers.

Examples of confocal fluorescence images from laser scanning (LSC 63.03 oil lens) from IGS. Immunoreactivity towards ESR1, ESR2, PGR and PRLR can be observed in apocrine gland cells labeled with PE and stained for the different receptors (green fluorescence). Use of To-Pro-3 iodide for nuclear counterstain (red fluorescence).

Post-parturient behavior of mammalian females is essential for early parent–offspring contact. After delivery, lambs need to ingest colostrum for obtaining the related immunological protection, and early interactions between the mother and the lamb are crucial. Despite visual and auditory cues, olfactory cues are decisive in lamb orientation to the.