Embryonic/fetal membrane slipping
Keywords: membrane, slip, fetus, embryo, diagnosis, pregnancy, ruminant, bovine, ovine, caprine, staging.
Membrane slip is commonly used to diagnose pregnancy in cattle, especially in dairy cattle where early pregnancy diagnosis is important. Membrane slip manifests itself when gentle pressure is applied to a fold of the uterine wall. If a conceptus is present, its free allantois or allantochorion or even the free chorion itself, slips away from the constricted section of the uterus. This creates a distinct, palpable "click" between the operator's fingers.
The composite image below shows how a membrane slip is generated. In image A, the uterus is grasped between the thumb and any finger, then the digits are rolled relative to one another until a firm clicking sensation is detected. The operators digits are not moved off the uterus at any time during this operation. Using an opened, pregnant uterus in image B, one can see how the edge of embryonic/fetal membrane (yellow arrows) is pinched gently between the operator's thumb and finger. As these digits are rolled relative to one another (decreasing the interposing angle between the thumb and finger) the membrane escapes the operator's grip (red and yellow arrows in image C) generating the clicking sensation.
Image size: 1024 x 768px.
In several studies, membrane slipping has been shown to be harmless to the conceptus.
As reviewed elsewhere in LORI, during early gestation, the allantois is not yet attached to the chorion. However, these two membranes gradually become inseparable and collectively, are known as the allantochorion or less commonly, the chorioallantois. Therefore in early gestation, it is either the allantois or chorion or allantochorion that is involved in membrane slipping; a fairly trivial point.
| Although the production of pregnancy specific proteins, RNA segments and Interferon Tau have been developed for early pregnancy detection in cattle, ultrasongraphy is currently accepted as the gold standard for comparison of pregnancy diagnostic methods in cattle; it is both highly specific and sensitive after 28 days of gestation and especially valuable for the diagnosis of twins. However, membrane slipping continues to be a valuable diagnostic tool for routine pregnancy diagnosis. Membrane slipping is also a useful tool for the detection of early pregnancy in small ruminants and wild ruminants when laparotomy is performed for any reason. It cannot be used in new world camelids or equids because of the diffuse placental attachment in those animals. |
Comment on the use of the word "fetal" in fetal membrane slip, still a widely accepted term in animal science:
It has been stated that the embryonic period in cattle extends from fertilization to the completion of differentiation at about 42 days (Committee on Reproductive Nomenclature, 1972. Recommendations for standardizing bovine reproductive terms. Cornell Vet 62: 216–237). However it is arguable that differentiation continues throughout pregnancy or even postnatal life and therefore, that the distinction between an embryo and fetus is arbitrary. Even in humans, where an embryo makes its sudden and completely artificial transition into fetal life at 8 weeks, this terminology is under review. Therefore, in this author's opinion, it is erroneous to use fetal membrane slip as a general diagnostic term in cattle, especially dairy cattle. This is because fetal membrane slip is most often used as a diagnostic tool before 42 days, when the conceptus is still formally classified as an embryo. This may be a trivial matter (and in the greater scheme of things, probably is) but like the term embryotomy it should probably be discarded in favor of a more global and accurate term. In that light, the author suggests that instead of the term fetal membrane slip, consideration be given instead, to using the term membrane slip throughout pregnancy.
Selected references:
Ioannidis, J. 2016. Circulating miRNA signatures of early pregnancy in cattle. BMC Genomics. 17: 184
Nation, D.P. et al. 2003. Accuracy of bovine pregnancy detection using transrectal ultrasonography at 28 to 35 days after insemination. Australian Vet. J. 81: 63–65
Preeti Rawat et al. 2016. Identification of potential protein biomarkers for early detection of pregnancy in cow urine using 2D DIGE and label free quantitation. Clin Proteomics. 13: 15.
Romano, J.E. 2006. Early pregnancy diagnosis by transrectal ultrasonography in dairy cattle.
Theriogenology. 66:1034–1041
