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.

Normal lochia from a dairy cow

Keywords: lochia, postpartum, bovine, cow, involution, uterus

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Normal lochia from a dairy cow at 12 days postpartum; seen in its bedding. At this time, the sloughing process of the caruncles reaches the capillary beds, releasing red blood cells into the lumen. Therefore this discharge is normal and in the absence of fever, inappetence and other common pathology at calving (mastitis, traumatic reticulo-pericarditis etc) it requires no treatment.

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 cervix of a postpartum cow

Keywords: cervix, involution, bovine, cow, endometrium, lochia

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The cervix of a cow seen at approximately one week after calving. This animal was euthanized because of a skeletal injury sustained during the birth of twin calves. Minor contusion and lacerations such as those seen here are common after parturition.

The bovine cervix closes down fairly rapidly after calving so that at this time (about a week after calving) it is difficult to introduce a hand into the uterus. However, the cervix remains open for at least 20 days to allow the discharge of lochia. This lochia becomes hemorrhagic at about 10 to 12 days when the remnants of the caruncles of pregnancy are sloughed to the level of the endometrial capilliary beds. It is also at about this time that the lochia begin to become purulent in nature as neutrophils enter the lumen from the capilliary beds. Therefore, if this photograph had been taken a few days later, it would not be unusual to find a hemorrhagic and somewhat purulent discharge being voided through the cervix.

Normal postpartum bovine uterus.

Keywords: postpartum, suckling, beef, dairy, lochia, involution, uterus, estrus, ovulation

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A normal completely-involuted bovine uterus. Note to the typical Y-shaped structure with a short body and two long horns. In the left ovary, a follicle approximately 2 cm in size can be seen developing. In the contralateral (right) ovary, there appeared to be no significant structures. This is typical of a postpartum reproductive tract in a suckled beef cow.. Cows (milk but not suckled) may ovulate as soon as 10 or 14 days after calving, long before the uterus has even involuted.