Uterus, 20 days postpartum

Keywords: bovine, uterus, caruncles, palpation, involution, postpartum, follicles

During transrectal palpation, one can place a hand over the cranial margin of the uterus by about 10 to 12 days after calving. By 20 days (as in this case) one can usually retract the uterus for palpation. Although tissue from the caruncles has been shed down to the capillary layer by 10 to 14 days postpartum, the bases of the caruncles (white arrows) are still palpable at this time. If the endometrium is exposed, they are obvious, even at 30 to 35 days, when the uterus is fully involuted. Incidentally, lochial discharge is almost complete in normal cows (suckled or non-sucked) by this stage of involution.

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Note that there is substantial ovarian activity in the form of follicle growth (yellow arrows) serving to remind one that FSH is not a limiting factor in the return to cyclicity in cattle. Follicles may ovulate as early as 10 to 14 days in non-suckled (dairy) cows but even though follicles such as these are present early in the postpartum period in almost all cattle, suckled cattle ovulate much later, LH being the limiting factor in those animals.

Uterine retraction

Keywords: retraction, uterus, palpation, amnion, membrane, slip, uterus, ovaries, examination, pregnancy diagnosis

The image below illustrates in part, a technique known as uterine retraction. Uterine retraction is in essence, the process of bringing the whole reproductive tract into reach for easy and accurate examination. The tract is passed through ones hand without releasing it through the entire examination.

The parts of the tract and its adnexa have been labeled in the black and white image below, serving as a key for the main image.

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There are variations as to how an operator may retract the uterus during transrectal palpation. Some may place a thumb under the lateral aspect of a uterine horn, lifting the horn so that the ventral inter-cornual ligament can be brought close enough to grasp. This technique has been referred to as "indirect" retraction. Others (including the author) prefer a "direct" method, grasping the cervix around its circumference and moving it caudo-dorsally so the intercornual ligament is elevated and made accessible.

The ventral intercornual ligament is larger and stronger than the dorsal ligament. Therefore, only the ventral ligament is used to retract the uterus.

Once the intercornual ligaments are accessible, the ventral intercornual ligament is hooked with one or more fingers. Then the uterine horns are raised and "flipped" dorso-caudally so that the tract becomes doubled over on itself. It is held in this position while the operator's hand "crawls" along the uterine horns, "feeding" them under the hand at the same time. The uterus is examined for fetal membrane slipping and abnormalities such as free fluid, tumors and so on. Like the uterus, the ovaries and their adnexa can be moved extensively in cattle. Therefore the ovary on either side can be reached easily in most animals through the "crawling" and "feeding" motions described above.

In some animals rectal tone makes it difficult to palpate structures and patience is called for. In cows with epidural anesthesia, the rectum may dilate with air, also making transrectal palpation a challenge.

Although retraction is not necessary in every case, it is usually essential for accurate assessment of the tract. When structures such as early pregnancies are not detected, it is usually because the operator has grasped sections of the uterus and has dropped the tract intermittently during palpation.

Note on retraction in other species: Although camelids do not have an intercornual ligament, the non-pregnant uterus can be retracted by cupping the whole uterus and flipping it up in a dorso-caudal direction. Great caution must be exercised when examining smaller camelids; in some alpacas it may not be possible to perform transrectal palpation safely. In horses it is neither possible nor necessary to retract the uterus for accurate transrectal examination. The equine tract is well suspended by the mesometrium, making its position predictable and easy to locate. Also, mesocervical and mesometrial tension in mares make it impossible to grasp the cervix and retract the uterus.

Bovine uterine involution

Key words: bovine, involution, uterus, cycling, estrous, cycles, postpartum, palpation

The uterus of a cow, two weeks after calving, opened to show the state of involution. At this stage of involution, the areas of the endometrium have already involuted (this occurs by about 10 days after calving) but the caruncles themselves have not even sloughed their epithelium completely. It is only by 12 to 14 days that (at about the stage of the uterus in this image) that the sloughing process reaches the capillary beds, releasing red blood cells into the lumen. It also at this time, that neutrophils enter the lumen, attracted by chemotaxis to the contaminated lochia. Therefore lochia that are somewhat purulent and blood tinged at this time are normal.

The contents of the uterus are normally contaminated (not infected) by bacteria up until 25 to 30 days postpartum. The bacterial swab in the inset has been added as a reminder to this fact. Uterine cultures taken before this time are of limited value.

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During transrectal palpation, it is only possible to grasp the cranial border of the uterus by this stage of involution i.e. 10 to 14 days after calving; much later than in mares. The size of an average human hand is given to scale to allow one to appreciate that challenge. Depending on management and health of the animal it has returned to its pre-pregnancy size by about 35 days after calving; in some reports as early as 25 days; in others, as late as 50 days. It is easily retracted at that time. After calving, the uterus of a cow is always larger than that of a heifer.

Although the corpus luteum of pregnancy is visible for several weeks after parturition (see the inset at right above) it has ceased to function at the time of calving.

Uterine involution is, for all practical purposes, disconnected from ovarian function in cattle. It is also disconnected from estrous behavior. In dairy cows (where human interference prevents calves from suckling) the first ovulations after calving often occur before 20 days postpartum but those ovulations are seldom accompanied by signs of estrus. Over the next two to three ovulations (which occur at increasing intervals between one another) estrous display becomes more obvious. Interestingly, the process of uterine involution is slower than both the resumption of normal ovarian activity and estrous display.

Although the epithelial regeneration over the caruncles is largely complete by 30 to 35 days postpartum, global involution of the uterus continues over the next 10 to 15 days. Certainly, the uterus is completely involuted by 70 to 75 days, when the first inseminations start occurring after calving in most dairy cattle i.e. the "voluntary waiting period". In beef animals, where suckling occurs, and breed and energy intake can also have profound negative effects on postpartum anestrous intervals, uterine involution is complete long before re-breeding occurs and is seldom a limiting factor in postpartum fertility.

Note of interest: Although the complex physiology of postpartum anestrus (nutrition, breed, presence of milk in the udder, calf contact etc) is still not completely understood, one of the cornerstones of anestrus appears to be a lack of LH secretion. Strangely, FSH secretion is a not a limiting factor in the resumption of cyclicity, well developed follicle populations being plentiful well before the first ovulations occur. A major negative effect on LH secretion is that of endogenous opioids (endorphins). This is not only true for cattle in the postpartum period but for mammals in general, including humans. LH secretion increases almost immediately after morphine antagonists such as naloxone and naltrexone are administered.

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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