The corpus luteum and corpus albicans.
Keywords: CL, bovine, cow, palpation, progesterone
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The crown of a corpus luteum (CL) in an ovary of a cow. The CL is a source of progesterone and several other hormones, including relaxin, müllerian inhibiting hormone, inhibin and even GnRH.
A CL is easily palpable per rectum in most cases and is useful for determining if the cow is having estrous cycles and in some cases, assisting one in staging the estrous cycle. The crown of a corpus luteum is seen in all species except horses where the tunica albuginea does not allow the follicle to ovulate through the surface of the ovary.
After ovulation, blood fills the antrum of the follicle, coagulating and forming a corpus hemorrhagicum. As this blood is phagocytosed, the theca granulosa of the ovarian follicle undergoes both hyperplasia and hypertrophy, folding in towards the center of the antrum.
This image shows the size of a mature CL, the author's thumb depressing the cut surface of that structure in a transected ovary.
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In the example shown below, that folding is clearly visible.
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After luteolysis, the corpus luteum undergoes regression and shrinks, forming a corpus albicans. The term "albicans" is derived from the Latin word for white but in domestic animals, this is practically a misnomer. In fact it is only in a few animals (cetaceans for example) where the corpus albicans remains as a large, substantial structure after luteolysis. In domestic animals it only becomes a small, white body long after luteolysis is complete and in fact, is often invisible to the naked eye by that time. Indeed, at the end of the luteal phase in domestic animals, when it is commonly referred to as a corpus alicans, the corpus "albicans" (CA) is a dark yellow-to-bright orange structure as shown here.
A CA is seen below, advanced in its luteolysis and degeneration, evidence by rays of fibrous tissue in the structure. Note that this luteal structure has a cavity in the center; a common finding in luteal tissue in cattle. It is not abnormal and is merely a function of luteinization from the theca granulosa growing but never reaching the center of what was previously a follicle. Instead of being referred to as a cystic CL/CA it is often labeled a "luteal cyst".
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